The mushroom cloud of the atomic bombing of Nagasaki, Japan in 1945 rose some 18 kilometers (11 miles) above the bomb’s hypocenter.

Nuclear weapons
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A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter; a modern thermonuclear weapon weighing little more than a thousand kilograms can produce an explosion comparable to the detonation of more than a billion kilograms of conventional high explosive.^[1] Even small nuclear devices can devastate a city. Nuclear weapons are considered weapons of mass destruction, and their use and control has been a major aspect of international policy since their debut.

In the history of warfare, only two nuclear weapons have been detonated offensively, both near the end of World War II. The first was detonated on the morning of 6 August 1945, when the United States dropped a uranium gun-type device code-named “Little Boy” on the Japanese city of Hiroshima. The second was detonated three days later when the United States dropped a plutonium implosion-type device code-named “Fat Man” on the city of Nagasaki, Japan. These bombings resulted in the immediate deaths of around 120,000 people (mostly civilians) from injuries sustained from the explosion and acute radiation sickness, and even more deaths from long-term effects of ionizing radiation. The use of these weapons was and remains controversial. (See atomic bombings of Hiroshima and Nagasaki for a full discussion.)

Since the Hiroshima and Nagasaki bombings, nuclear weapons have been detonated on over two thousand occasions for testing purposes and demonstration purposes. The only countries known to have detonated nuclear weapons—and that acknowledge possessing such weapons—are (chronologically) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, the People’s Republic of China, India, Pakistan, and North Korea. Israel is also widely believed to possess nuclear weapons, though it does not acknowledge having them. (For more information on these states’ nuclear programs, as well as other states that formerly possessed nuclear weapons or are suspected of seeking nuclear weapons, see list of states with nuclear weapons.)

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Types of nuclear weapons

The two basic fission weapon designs

There are two basic types of nuclear weapon. The first type produces its explosive energy through nuclear fission reactions alone. Such fission weapons also commonly referred to as atomic bombs or atom bombs (abbreviated as A-bombs), though their energy comes specifically from the nucleus of the atom.

In fission weapons, a mass of fissile material (enriched uranium or plutonium) is assembled into a supercritical mass—the amount of material needed to start an exponentially growing nuclear chain reaction—either by shooting one piece of sub-critical material into another (the “gun” method), or by compressing a sub-critical sphere of material using chemical explosives to many times its original density (the “implosion” method). The latter approach is considered more sophisticated than the former, and only the latter approach can be used if plutonium is the fissile material.

A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range between the equivalent of less than a ton of TNT upwards to around 500,000 tons (500 kilotons) of TNT.^[2]

The second basic type of nuclear weapon produces a large amount of its energy through nuclear fusion reactions. Such fusion weapons are generally referred to as thermonuclear weapons or more colloquially as hydrogen bombs (abbreviated as H-bombs), as they rely on fusion reactions between isotopes of hydrogen (deuterium and tritium). However, all such weapons derive a significant portion – and sometimes a majority – of their energy from fission (including fission induced by neutrons from fusion reactions). Unlike fission weapons, there are no inherent limits on the energy released by thermonuclear weapons. Only six countries—United States, Russia, United Kingdom, People’s Republic of China, France and India—have conducted thermonuclear weapon tests. (Whether India has detonated a “true,” multi-staged thermonuclear weapon is controversial.)^[3]

The basics of the Teller–Ulam design for a hydrogen bomb: a fission bomb uses radiation to compress and heat a separate section of fusion fuel.

Thermonuclear bombs work by using the energy of a fission bomb in order to compress and heat fusion fuel. In the Teller-Ulam design, which accounts for all multi-megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel (tritium, deuterium, or lithium deuteride) in proximity within a special, radiation-reflecting container. When the fission bomb is detonated, gamma and X-rays emitted first compress the fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-speed neutrons, which then can induce fission in materials which normally are not prone to it, such as depleted uranium. Each of these components is known as a “stage,” with the fission bomb as the “primary” and the fusion capsule as the “secondary.” In large hydrogen bombs, about half of the yield, and much of the resulting nuclear fallout, comes from the final fissioning of depleted uranium.^[2] By chaining together numerous stages with increasing amounts of fusion fuel, thermonuclear weapons can be made to an almost arbitrary yield; the largest ever detonated (the Tsar Bomba of the USSR) released an energy equivalent to over 50 million tons (50 megatons) of TNT. Most thermonuclear weapons are considerably smaller than this, due for instance to practical constraints in fitting them into the space and weight requirements of missile warheads.^[4]

There are other types of nuclear weapons as well. For example, a boosted fission weapon is a fission bomb which increases its explosive yield through a small amount of fusion reactions, but it is not a fusion bomb. In the boosted bomb, the neutrons produced by the fusion reactions serve primarily to increase the efficiency of the fission bomb. Some weapons are designed for special purposes; a neutron bomb is a thermonuclear weapon that yields a relatively small explosion but a relatively large amount of neutron radiation; such a device could theoretically be used to cause massive casualties while leaving infrastructure mostly intact and creating a minimal amount of fallout. The detonation of a nuclear weapon is accompanied by a blast of neutron radiation. Surrounding a nuclear weapon with suitable materials (such as cobalt or gold) creates a weapon known as a salted bomb. This device can produce exceptionally large quantities of radioactive contamination. Most variety in nuclear weapon design is in different yields of nuclear weapons for different types of purposes, and in manipulating design elements to attempt to make weapons extremely small.^[2]

Nuclear strategy

The United States’ Peacekeeper missile was a MIRVed delivery system. Each missile could contain up to ten nuclear warheads (shown in red), each of which could be aimed at a different target. These were developed to make missile defense very difficult for an enemy country

Nuclear warfare strategy is a way for either fighting or avoiding a nuclear war. The policy of trying to ward off a potential attack by a nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence. The goal in deterrence is to always maintain a second strike status (the ability of a country to respond to a nuclear attack with one of its own) and potentially to strive for first strike status (the ability to completely destroy an enemy‘s nuclear forces before they could retaliate). During the Cold War, policy and military theorists in nuclear-enabled countries worked out models of what sorts of policies could prevent one from ever being attacked by a nuclear weapon.

Different forms of nuclear weapons delivery (see below) allow for different types of nuclear strategy, primarily by making it difficult to defend against them and difficult to launch a pre-emptive strike against them. Sometimes this has meant keeping the weapon locations hidden, such as putting it on submarines or train cars whose locations are very hard for an enemy to track, and other times this means burying them in hardened bunkers. Other responses have included attempts to make it seem likely that the country could survive a nuclear attack, by using missile defense (to destroy the missiles before they land) or by means of civil defense (using early warning systems to evacuate citizens to a safe area before an attack). Note that weapons which are designed to threaten large populations or to generally deter attacks are known as strategic weapons. Weapons which are designed to actually be used on a battlefield in military situations are known as tactical weapons.

There are critics of the very idea of nuclear strategy for waging nuclear war who have suggested that a nuclear war between two nuclear powers would result in mutual annihilation. From this point of view, the significance of nuclear weapons is purely to deter war because any nuclear war would immediately escalate out of mutual distrust and fear, resulting in mutually assured destruction. This threat of national, if not global, destruction has been a strong motivation for anti-nuclear weapons activism.

Critics from the peace movement and within the military establishment have questioned the usefulness of such weapons in the current military climate. The use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, according to an advisory opinion issued by the International Court of Justice in 1996.

Perhaps the most controversial idea in nuclear strategy is that nuclear proliferation would be desirable. This view argues that, unlike conventional weapons, nuclear weapons successfully deter all-out war between states, as they did during the Cold War between the U.S. and the Soviet Union. Political scientist Kenneth Waltz is the most prominent advocate of this argument.

It has been claimed that the threat of potentially suicidal terrorists possessing nuclear weapons (a form of nuclear terrorism) complicates the decision process. Mutually assured destruction may not be effective against an enemy who expects to die in a confrontation, as they may feel they will be rewarded in a religious afterlife as martyrs and would not therefore be deterred by a sense of self-preservation. Further, if the initial act is from rogue groups of individuals instead of a nation, there is no fixed nation or fixed military targets to retaliate against. It has been argued, especially after the September 11, 2001 attacks, that this complication is the sign of the next age of nuclear strategy, distinct from the relative stability of the Cold War.^[5]

Weapons delivery

The first nuclear weapons were gravity bombs, such as the “Fat Man” weapon dropped on Nagasaki, Japan. These weapons were very large and could only be delivered by a bomber aircraft

Nuclear weapons delivery—the technology and systems used to bring a nuclear weapon to its target—is an important aspect of nuclear weapons relating both to nuclear weapon design and nuclear strategy. Additionally, developing and maintaining delivery options is among the most resource-intensive aspects of nuclear weapons: according to one estimate, deployment of nuclear weapons accounted for 57% of the total financial resources spent by the United States in relation to nuclear weapons since 1940.^[6]

Historically the first method of delivery, and the method used in the two nuclear weapons actually used in warfare, is as a gravity bomb, dropped from bomber aircraft. This method is usually the first developed by countries as it does not place many restrictions on the size of the weapon, and weapon miniaturization is something which requires considerable weapons design knowledge. It does, however, limit the range of attack, the response time to an impending attack, and the number of weapons which can be fielded at any given time. Additionally, specialized delivery systems are usually not necessary; especially with the advent of miniaturization, nuclear bombs can be delivered by both strategic bombers and tactical fighter-bombers, allowing an air force to use its current fleet with little or no modification. This method may still be considered the primary means of nuclear weapons delivery; the majority of U.S. nuclear warheads, for example, are represented in free-fall gravity bombs, namely the B61.^[2]

More preferable from a strategic point of view are nuclear weapons mounted onto a missile, which can use a ballistic trajectory to deliver a warhead over the horizon. While even short range missiles allow for a faster and less vulnerable attack, the development of intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) has allowed some nations to plausibly deliver missiles anywhere on the globe with a high likelihood of success. More advanced systems, such as multiple independently targetable reentry vehicles (MIRVs) allow multiple warheads to be launched at several targets from any one missile, reducing the chance of any successful missile defense. Today, missiles are most common among systems designed for delivery of nuclear weapons. Making a warhead small enough to fit onto a missile, though, can be a difficult task.^[2]

Tactical weapons (see above) have involved the most variety of delivery types, including not only gravity bombs and missiles but also artillery shells, land mines, and nuclear depth charges and torpedoes for anti-submarine warfare. An atomic mortar was also tested at one time by the United States. Small, two-man portable tactical weapons (somewhat misleadingly referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty to combine sufficient yield with portability limits their military utility.^[2]

Governance, control, and law

The International Atomic Energy Agency was created in 1957 in order to encourage the peaceful development of nuclear technology while providing international safeguards against nuclear proliferation

Because of the immense military power they can confer, the political control of nuclear weapons has been a key issue for as long as they have existed; in most countries the use of nuclear force can only be authorized by the head of government.^[7]

In the late 1940s, lack of mutual trust was preventing the United States and the Soviet Union from making ground towards international arms control agreements, but by the 1960s steps were being taken to limit both the proliferation of nuclear weapons to other countries and the environmental effects of nuclear testing. The Partial Test Ban Treaty (1963) restricted all nuclear testing to underground nuclear testing, to prevent contamination from nuclear fallout, while the Nuclear Non-Proliferation Treaty (1968) attempted to place restrictions on the types of activities which signatories could participate in, with the goal of allowing the transference of non-military nuclear technology to member countries without fear of proliferation. In 1957, the International Atomic Energy Agency (IAEA) was established under the mandate of the United Nations in order to encourage the development of the peaceful applications of nuclear technology, provide international safeguards against its misuse, and facilitate the application of safety measures in its use. In 1996, many nations signed and ratified the Comprehensive Test Ban Treaty which prohibits all testing of nuclear weapons, which would impose a significant hindrance to their development by any complying country.^[8]

Additional treaties have governed nuclear weapons stockpiles between individual countries, such as the SALT I and START I treaties, which limited the numbers and types of nuclear weapons between the United States and the Soviet Union.

Nuclear weapons have also been opposed by agreements between countries. Many nations have been declared Nuclear-Weapon-Free Zones, areas where nuclear weapons production and deployment are prohibited, through the use of treaties. The Treaty of Tlatelolco (1967) prohibited any production or deployment of nuclear weapons in Latin America and the Caribbean, and the Treaty of Pelindaba (1964) prohibits nuclear weapons in many African countries. As recently as 2006 a Central Asian Nuclear Weapon Free Zone was established amongst the former Soviet republics of Central Asia prohibiting nuclear weapons.

In the middle of 1996, the International Court of Justice, the highest court of the United Nations, issued an Advisory Opinion concerned with the “Legality of the Threat or Use of Nuclear Weapons“. The court ruled that the use or threat of use of nuclear weapons would violate various articles of international law, including the Geneva Conventions, the Hague Conventions, the UN Charter, and the Universal Declaration of Human Rights.

Additionally, there have been other, specific actions meant to discourage countries from developing nuclear arms. In the wake of the tests by India and Pakistan in 1998, economic sanctions were (temporarily) levied against both countries, though neither were signatories with the Nuclear Non-Proliferation Treaty. One of the stated casus belli for the initiation of the 2003 Iraq War was an accusation by the United States that Iraq was actively pursuing nuclear arms (though this was soon discovered not to be the case as the program had been discontinued). In 1981, Israel had bombed a nuclear reactor in Osirak, Iraq, in what it called an attempt to halt Iraq’s previous nuclear arms ambitions.^{[citation needed]}

The name atom comes from the Greek ἄτομος/átomos, α-τεμνω, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the ‘atom’ was not indivisible. The principles of quantum mechanics were used to successfully model the atom.[1][2]

Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom’s mass is concentrated in the nucleus,[note 1] with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus.[3] Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom’s magnetic properties.
Contents
[hide]

* 1 History
* 2 Components
o 2.1 Subatomic particles
o 2.2 Nucleus
o 2.3 Electron cloud
* 3 Properties
o 3.1 Nuclear properties
o 3.2 Mass
o 3.3 Size
o 3.4 Radioactive decay
o 3.5 Magnetic moment
o 3.6 Energy levels
o 3.7 Valence and bonding behavior
o 3.8 States
* 4 Identification
* 5 Origin and current state
o 5.1 Nucleosynthesis
o 5.2 Earth
o 5.3 Rare and theoretical forms
* 6 See also
* 7 Notes
* 8 References
o 8.1 Book references
* 9 External links

History
Main articles: Atomic theory and Atomism

The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny quantities has been around for millennia, but these ideas were founded in abstract, philosophical reasoning rather than experimentation and empirical observation. The nature of atoms in philosophy varied considerably over time and between cultures and schools, and often had spiritual elements. Nevertheless, the basic idea of the atom was adopted by scientists thousands of years later because it elegantly explained new discoveries in the field of chemistry.[4]

The earliest references to the concept of atoms date back to ancient India in the 6th century BCE.[5] The Nyaya and Vaisheshika schools developed elaborate theories of how atoms combined into more complex objects (first in pairs, then trios of pairs).[6] The references to atoms in the West emerged a century later from Leucippus whose student, Democritus, systemized his views. In approximately 450 BCE, Democritus coined the term átomos (Greek: ἄτομος), which means “uncuttable” or “the smallest indivisible particle of matter”, i.e., something that cannot be divided. Although the Indian and Greek concepts of the atom were based purely on philosophy, modern science has retained the name coined by Democritus.[4]

Further progress in the understanding of atoms did not occur until the science of chemistry began to develop. In 1661, natural philosopher Robert Boyle published The Sceptical Chymist in which he argued that matter was composed of various combinations of different “corpuscules” or atoms, rather than the classical elements of air, earth, fire and water.[7] In 1789 the term element was defined by the French nobleman and scientific researcher Antoine Lavoisier to mean basic substances that could not be further broken down by the methods of chemistry.[8]
Various atoms and molecules as depicted in John Dalton’s A New System of Chemical Philosophy (1808).

In 1803, English instructor and natural philosopher John Dalton used the concept of atoms to explain why elements always react in a ratio of small whole numbers—the law of multiple proportions—and why certain gases dissolve better in water than others. He proposed that each element consists of atoms of a single, unique type, and that these atoms can join together to form chemical compounds.[9][10]

Additional validation of particle theory (and by extension atomic theory) occurred in 1827 when botanist Robert Brown used a microscope to look at dust grains floating in water and discovered that they moved about erratically—a phenomenon that became known as “Brownian motion”. J. Desaulx suggested in 1877 that the phenomenon was caused by the thermal motion of water molecules, and in 1905 Albert Einstein produced the first mathematical analysis of the motion.[11][12][13] French physicist Jean Perrin used Einstein’s work to experimentally determine the mass and dimensions of atoms, thereby conclusively verifying Dalton’s atomic theory.[14]

The physicist J. J. Thomson, through his work on cathode rays in 1897, discovered the electron and its subatomic nature, which destroyed the concept of atoms as being indivisible units.[15] Thomson believed that the electrons were distributed throughout the atom, with their charge balanced by the presence of a uniform sea of positive charge (the plum pudding model).

However, in 1909, researchers under the direction of physicist Ernest Rutherford bombarded a sheet of gold foil with helium ions and discovered that a small percentage were deflected through much larger angles than was predicted using Thomson’s proposal. Rutherford interpreted the gold foil experiment as suggesting that the positive charge of an atom and most of its mass was concentrated in a nucleus at the center of the atom (the Rutherford model), with the electrons orbiting it like planets around a sun. Positively charged helium ions passing close to this dense nucleus would then be deflected away at much sharper angles.[16]

While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table.[17] The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element. J.J. Thomson created a technique for separating atom types through his work on ionized gases, which subsequently led to the discovery of stable isotopes.[18]
A Bohr model of the hydrogen atom, showing an electron jumping between fixed orbits and emitting a photon of energy with a specific frequency.

Meanwhile, in 1913, physicist Niels Bohr revised Rutherford’s model by suggesting that the electrons were confined into clearly defined, quantized orbits, and could jump between these, but could not freely spiral inward or outward in intermediate states.[19] An electron must absorb or emit specific amounts of energy to transition between these fixed orbits. When the light from a heated material was passed through a prism, it produced a multi-colored spectrum. The appearance of fixed lines in this spectrum was successfully explained by the orbital transitions.[20]

Chemical bonds between atoms were now explained, by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons.[21] As the chemical properties of the elements were known to largely repeat themselves according to the periodic law,[22] in 1919 the American chemist Irving Langmuir suggested that this could be explained if the electrons in an atom were connected or clustered in some manner. Groups of electrons were thought to occupy a set of electron shells about the nucleus.[23]

The Stern–Gerlach experiment of 1922 provided further evidence of the quantum nature of the atom. When a beam of silver atoms was passed through a specially-shaped magnetic field, the beam was split based on the direction of an atom’s angular momentum, or spin. As this direction is random, the beam could be expected to spread into a line. Instead, the beam was split into two parts, depending on whether the atomic spin was oriented up or down.[24]

In 1926, Erwin Schrödinger, using Louis de Broglie’s 1924 proposal that particles behave to an extent like waves, developed a mathematical model of the atom that described the electrons as three-dimensional waveforms, rather than point particles. A consequence of using waveforms to describe electrons is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at the same time; this became known as the uncertainty principle, formulated by Werner Heisenberg in 1926. In this concept, for each measurement of a position one could only obtain a range of probable values for momentum, and vice versa. Although this model was difficult to visualize, it was able to explain observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms larger than hydrogen. Thus, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to exist.[25][26]
Schematic diagram of a simple mass spectrometer.

The development of the mass spectrometer allowed the exact mass of atoms to be measured. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom’s mass to its charge. The chemist Francis William Aston used this instrument to demonstrate that isotopes had different masses. The mass of these isotopes varied by integer amounts, called the whole number rule.[27] The explanation for these different atomic isotopes awaited the discovery of the neutron, a neutral-charged particle with a mass similar to the proton, by the physicist James Chadwick in 1932. Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus.[28]

In the 1950s, the development of improved particle accelerators and particle detectors allowed scientists to study the impacts of atoms moving at high energies.[29] Neutrons and protons were found to be hadrons, or composites of smaller particles called quarks. Standard models of nuclear physics were developed that successfully explained the properties of the nucleus in terms of these sub-atomic particles and the forces that govern their interactions.[30]

Around 1985, Steven Chu and co-workers at Bell Labs developed a technique for lowering the temperatures of atoms using lasers. In the same year, a team led by William D. Phillips managed to contain atoms of sodium in a magnetic trap. The combination of these two techniques and a method based on the Doppler effect, developed by Claude Cohen-Tannoudji and his group, allows small numbers of atoms to be cooled to several microkelvin. This allows the atoms to be studied with great precision, and later led to the discovery of Bose-Einstein condensation.[31]

Historically, single atoms have been prohibitively small for scientific applications. Recently, devices have been constructed that use a single metal atom connected through organic ligands to construct a single electron transistor.[32] Experiments have been carried out by trapping and slowing single atoms using laser cooling in a cavity to gain a better physical understanding of matter.[33]

Components

Subatomic particles
Main article: Subatomic particle

Though the word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron. However, the hydrogen-1 atom has no neutrons and a positive hydrogen ion has no electrons.

The electron is by far the least massive of these particles at 9.11 × 10−31 kg, with a negative electrical charge and a size that is too small to be measured using available techniques.[34] Protons have a positive charge and a mass 1,836 times that of the electron, at 1.6726 × 10−27 kg, although this can be reduced by changes to the energy binding the proton into an atom. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of electrons,[35] or 1.6929 × 10−27 kg. Neutrons and protons have comparable dimensions—on the order of 2.5 × 10−15 m—although the ‘surface’ of these particles is not sharply defined.[36]

In the Standard Model of physics, both protons and neutrons are composed of elementary particles called quarks. The quark belongs to the fermion group of particles, and is one of the two basic constituents of matter—the other being the lepton, of which the electron is an example. There are six types of quarks, each having a fractional electric charge of either +2/3 or −1/3. Protons are composed of two up quarks and one down quark, while a neutron consists of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles. The quarks are held together by the strong nuclear force, which is mediated by gluons. The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces.[37][38]

Nucleus
Main article: Atomic nucleus
The binding energy needed for a nucleon to escape the nucleus, for various isotopes.

All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to \begin{smallmatrix}1.07 \sqrt[3]{A}\end{smallmatrix} fm, where A is the total number of nucleons.[39] This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other.[40]

Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay.[41]

The neutron and the proton are different types of fermions. The Pauli exclusion principle is a quantum mechanical effect that prohibits identical fermions (such as multiple protons) from occupying the same quantum physical state at the same time. Thus every proton in the nucleus must occupy a different state, with its own energy level, and the same rule applies to all of the neutrons. (This prohibition does not apply to a proton and neutron occupying the same quantum state.)[42]

For atoms with low atomic numbers, a nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with roughly matching numbers of protons and neutrons are more stable against decay. However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which modifies this trend. Thus, there are no stable nuclei with equal proton and neutron numbers above atomic number Z = 20 (calcium); and as Z increases toward the heaviest nuclei, the ratio of neutrons per proton required for stability increases to about 1.5.[42]
Illustration of a nuclear fusion process that forms a deuterium nucleus, consisting of a proton and a neutron, from two protons. A positron (e+)—an antimatter electron—is emitted along with an electron neutrino.

The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3–10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse together into a single nucleus.[43] Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element.[44][45]

If the mass of the nucleus following a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values is emitted as energy, as described by Albert Einstein’s mass–energy equivalence formula, E = mc2, where m is the mass loss and c is the speed of light. This deficit is the binding energy of the nucleus.[46]

The fusion of two nuclei that have lower atomic numbers than iron and nickel is usually an exothermic process that releases more energy than is required to bring them together.[47] It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the total binding energy begins to decrease. That means fusion processes with nuclei that have higher atomic numbers is an endothermic process. These more massive nuclei can not undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star.[42]

Electron cloud
Main articles: Electron cloud and Atomic orbital
A potential well, showing the minimum energy V(x) needed to reach each position x. A particle with energy E is constrained to a range of positions between x1 and x2.

The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed in order for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations.

Electrons, like other particles, have properties of both a particle and a wave. The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing wave—a wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital, a mathematical function that characterises the probability that an electron will appear to be at a particular location when its position is measured.[48] Only a discrete (or quantized) set of these orbitals exist around the nucleus, as other possible wave patterns will rapidly decay into a more stable form.[49] Orbitals can have one or more ring or node structures, and they differ from each other in size, shape and orientation.[50]
Wave functions of the first five atomic orbitals. The three 2p orbitals each display a single angular node that has an orientation and a minimum at the center.

Each atomic orbital corresponds to a particular energy level of the electron. The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission, an electron in a higher energy state can drop to a lower energy state while radiating the excess energy as a photon. These characteristic energy values, defined by the differences in the energies of the quantum states, are responsible for atomic spectral lines.[49]

The amount of energy needed to remove or add an electron (the electron binding energy) is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom,[51] compared to 2.23 Mev for splitting a deuterium nucleus.[52] Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals.[53]

Properties

Nuclear properties
Main articles: Isotope, Stable isotope, and List of elements by nuclear stability

By definition, any two atoms with an identical number of protons in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of neutrons are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form, sometimes called protium), one neutron (deuterium), two neutrons (tritium) and more than two neutrons.[54] The known elements form a set of atomic numbers from hydrogen with a single proton up to the 118-proton element ununoctium.[55] All known isotopes of elements with atomic numbers greater than 82 are radioactive.[56][57]

About 339 nuclides occur naturally on Earth, of which 269 (about 79%) have not been observed to decay.[58] Of the chemical elements, 80 have one or more stable isotopes. Elements 43, 61, and all elements numbered 83 or higher have no stable isotopes. As a rule, there is, for each atomic number (each element) only a handful of stable isotopes, the average being 3.1 stable isotopes per element which has any stable isotopes. Twenty-seven elements have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten (for the element tin).[59]

Stability of isotopes is affected by the ratio of protons to neutrons, and also by presence of certain “magic numbers” of neutrons or protons which represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. Of the 250 known stable nuclides, only four have both an odd number of protons and odd number of neutrons: 2H, 6Li, 10B and 14N. Also, only four naturally-occurring, radioactive odd-odd nuclides have a half-life over a billion years: 40K, 50V, 138La and 180mTa. Most odd-odd nuclei are highly unstable with respect to beta decay, because the decay products are even-even, and are therefore more strongly bound, due to nuclear pairing effects.[59]

Mass
Main article: Atomic mass

Because the large majority of an atom’s mass comes from the protons and neutrons, the total number of these particles in an atom is called the mass number. The mass of an atom at rest is often expressed using the unified atomic mass unit (u), which is also called a Dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately 1.66 × 10−27 kg.[60] Hydrogen-1, the lightest isotope of hydrogen and the atom with the lowest mass, has an atomic weight of 1.007825 u.[61] An atom has a mass approximately equal to the mass number times the atomic mass unit.[62] The heaviest stable atom is lead-208,[56] with a mass of 207.9766521 u.[63]

As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles. The mole is defined such that one mole of any element will always have the same number of atoms (about 6.022 × 1023). This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element will have a mass of 0.001 kg, or 1 gram. Carbon, for example, has an atomic mass of 12 u, so a mole of carbon atoms weighs 0.012 kg.[60]

Size
Main article: Atomic radius

Atoms lack a well-defined outer boundary, so the dimensions are usually described in terms of the distances between two nuclei when the two atoms are joined in a chemical bond. The radius varies with the location of an atom on the atomic chart, the type of chemical bond, the number of neighboring atoms (coordination number) and a quantum mechanical property known as spin.[64] On the periodic table of the elements, atom size tends to increase when moving down columns, but decrease when moving across rows (left to right).[65] Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm.[66] These dimensions are thousands of times smaller than the wavelengths of light (400–700 nm) so they can not be viewed using an optical microscope. However, individual atoms can be observed using a scanning tunneling microscope.

Some examples will demonstrate the minuteness of the atom. A typical human hair is about 1 million carbon atoms in width.[67] A single drop of water contains about 2 sextillion (2 × 1021) atoms of oxygen, and twice the number of hydrogen atoms.[68] A single carat diamond with a mass of 2 × 10-4 kg contains about 10 sextillion (1022) atoms of carbon.[note 2] If an apple were magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple.[69]

Radioactive decay
Main article: Radioactive decay
This diagram shows the half-life (T½) in seconds of various isotopes with Z protons and N neutrons.

Every element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing the nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm.[70]

The most common forms of radioactive decay are:[71][72]

* Alpha decay is caused when the nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. The result of the emission is a new element with a lower atomic number.
* Beta decay is regulated by the weak force, and results from a transformation of a neutron into a proton, or a proton into a neutron. The first is accompanied by the emission of an electron and an antineutrino, while the second causes the emission of a positron and a neutrino. The electron or positron emissions are called beta particles. Beta decay either increases or decreases the atomic number of the nucleus by one.
* Gamma decay results from a change in the energy level of the nucleus to a lower state, resulting in the emission of electromagnetic radiation. This can occur following the emission of an alpha or a beta particle from radioactive decay.

Other more rare types of radioactive decay include ejection of neutrons or protons or clusters of nucleons from a nucleus, or more than one beta particle, or result (through internal conversion) in production of high-speed electrons which are not beta rays, and high-energy photons which are not gamma rays.

Each radioactive isotope has a characteristic decay time period—the half-life—that is determined by the amount of time needed for half of a sample to decay. This is an exponential decay process that steadily decreases the proportion of the remaining isotope by 50% every half life. Hence after two half-lives have passed only 25% of the isotope will be present, and so forth.[70]

Magnetic moment
Main articles: Electron magnetic dipole moment and Nuclear magnetic moment

Elementary particles possess an intrinsic quantum mechanical property known as spin. This is analogous to the angular momentum of an object that is spinning around its center of mass, although strictly speaking these particles are believed to be point-like and cannot be said to be rotating. Spin is measured in units of the reduced Planck constant (ħ), with electrons, protons and neutrons all having spin ½ ħ, or “spin-½”. In an atom, electrons in motion around the nucleus possess orbital angular momentum in addition to their spin, while the nucleus itself possesses angular momentum due to its nuclear spin.[73]

The magnetic field produced by an atom—its magnetic moment—is determined by these various forms of angular momentum, just as a rotating charged object classically produces a magnetic field. However, the most dominant contribution comes from spin. Due to the nature of electrons to obey the Pauli exclusion principle, in which no two electrons may be found in the same quantum state, bound electrons pair up with each other, with one member of each pair in a spin up state and the other in the opposite, spin down state. Thus these spins cancel each other out, reducing the total magnetic dipole moment to zero in some atoms with even number of electrons.[74]

In ferromagnetic elements such as iron, an odd number of electrons leads to an unpaired electron and a net overall magnetic moment. The orbitals of neighboring atoms overlap and a lower energy state is achieved when the spins of unpaired electrons are aligned with each other, a process known as an exchange interaction. When the magnetic moments of ferromagnetic atoms are lined up, the material can produce a measurable macroscopic field. Paramagnetic materials have atoms with magnetic moments that line up in random directions when no magnetic field is present, but the magnetic moments of the individual atoms line up in the presence of a field.[74][75]

The nucleus of an atom can also have a net spin. Normally these nuclei are aligned in random directions because of thermal equilibrium. However, for certain elements (such as xenon-129) it is possible to polarize a significant proportion of the nuclear spin states so that they are aligned in the same direction—a condition called hyperpolarization. This has important applications in magnetic resonance imaging.[76][77]

Energy levels
Main articles: Energy level and Atomic spectral line

When an electron is bound to an atom, it has a potential energy that is inversely proportional to its distance from the nucleus. This is measured by the amount of energy needed to unbind the electron from the atom, and is usually given in units of electronvolts (eV). In the quantum mechanical model, a bound electron can only occupy a set of states centered on the nucleus, and each state corresponds to a specific energy level. The lowest energy state of a bound electron is called the ground state, while an electron at a higher energy level is in an excited state.[78]

In order for an electron to transition between two different states, it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels. The energy of an emitted photon is proportional to its frequency, so these specific energy levels appear as distinct bands in the electromagnetic spectrum.[79] Each element has a characteristic spectrum that can depend on the nuclear charge, subshells filled by electrons, the electromagnetic interactions between the electrons and other factors.[80]
An example of absorption lines in a spectrum.

When a continuous spectrum of energy is passed through a gas or plasma, some of the photons are absorbed by atoms, causing electrons to change their energy level. Those excited electrons that remain bound to their atom will spontaneously emit this energy as a photon, traveling in a random direction, and so drop back to lower energy levels. Thus the atoms behave like a filter that forms a series of dark absorption bands in the energy output. (An observer viewing the atoms from a different direction, which does not include the continuous spectrum in the background, will instead see a series of emission lines from the photons emitted by the atoms.) Spectroscopic measurements of the strength and width of spectral lines allow the composition and physical properties of a substance to be determined.[81]

Close examination of the spectral lines reveals that some display a fine structure splitting. This occurs because of spin-orbit coupling, which is an interaction between the spin and motion of the outermost electron.[82] When an atom is in an external magnetic field, spectral lines become split into three or more components; a phenomenon called the Zeeman effect. This is caused by the interaction of the magnetic field with the magnetic moment of the atom and its electrons. Some atoms can have multiple electron configurations with the same energy level, which thus appear as a single spectral line. The interaction of the magnetic field with the atom shifts these electron configurations to slightly different energy levels, resulting in multiple spectral lines.[83] The presence of an external electric field can cause a comparable splitting and shifting of spectral lines by modifying the electron energy levels, a phenomenon called the Stark effect.[84]

If a bound electron is in an excited state, an interacting photon with the proper energy can cause stimulated emission of a photon with a matching energy level. For this to occur, the electron must drop to a lower energy state that has an energy difference matching the energy of the interacting photon. The emitted photon and the interacting photon will then move off in parallel and with matching phases. That is, the wave patterns of the two photons will be synchronized. This physical property is used to make lasers, which can emit a coherent beam of light energy in a narrow frequency band.[85]

Valence and bonding behavior
Main articles: Valence (chemistry) and Chemical bond

The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons in that shell are called valence electrons. The number of valence electrons determines the bonding behavior with other atoms. Atoms tend to chemically react with each other in a manner that will fill (or empty) their outer valence shells.[86] For example, a transfer of a single electron between atoms is a useful approximation for bonds which form between atoms which have one-electron more than a filled shell, and others which are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus, chemical bonding between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the organic compounds.[87]

The chemical elements are often displayed in a periodic table that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the noble gases.[88][89]

States
Main articles: State of matter and Phase (matter)
Snapshots illustrating the formation of a Bose–Einstein condensate.

Quantities of atoms are found in different states of matter that depend on the physical conditions, such as temperature and pressure. By varying the conditions, materials can transition between solids, liquids, gases and plasmas.[90] Within a state, a material can also exist in different phases. An example of this is solid carbon, which can exist as graphite or diamond.[91]

At temperatures close to absolute zero, atoms can form a Bose–Einstein condensate, at which point quantum mechanical effects, which are normally only observed at the atomic scale, become apparent on a macroscopic scale.[92][93] This super-cooled collection of atoms then behaves as a single super atom, which may allow fundamental checks of quantum mechanical behavior.[94]

Identification
Scanning tunneling microscope image showing the individual atoms making up this gold (100) surface. Reconstruction causes the surface atoms to deviate from the bulk crystal structure and arrange in columns several atoms wide with pits between them.

The scanning tunneling microscope is a device for viewing surfaces at the atomic level. It uses the quantum tunneling phenomenon, which allows particles to pass through a barrier that would normally be insurmountable. Electrons tunnel through the vacuum between two planar metal electrodes, on each of which is an adsorbed atom, providing a tunneling-current density that can be measured. Scanning one atom (taken as the tip) as it moves past the other (the sample) permits plotting of tip displacement versus lateral separation for a constant current. The calculation shows the extent to which scanning-tunneling-microscope images of an individual atom are visible. It confirms that for low bias, the microscope images the space-averaged dimensions of the electron orbitals across closely packed energy levels—the Fermi level local density of states.[95][96]

An atom can be ionized by removing one of its electrons. The electric charge causes the trajectory of an atom to bend when it passes through a magnetic field. The radius by which the trajectory of a moving ion is turned by the magnetic field is determined by the mass of the atom. The mass spectrometer uses this principle to measure the mass-to-charge ratio of ions. If a sample contains multiple isotopes, the mass spectrometer can determine the proportion of each isotope in the sample by measuring the intensity of the different beams of ions. Techniques to vaporize atoms include inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry, both of which use a plasma to vaporize samples for analysis.[97]

A more area-selective method is electron energy loss spectroscopy, which measures the energy loss of an electron beam within a transmission electron microscope when it interacts with a portion of a sample. The atom-probe tomograph has sub-nanometer resolution in 3-D and can chemically identify individual atoms using time-of-flight mass spectrometry.[98]

Spectra of excited states can be used to analyze the atomic composition of distant stars. Specific light wavelengths contained in the observed light from stars can be separated out and related to the quantized transitions in free gas atoms. These colors can be replicated using a gas-discharge lamp containing the same element.[99] Helium was discovered in this way in the spectrum of the Sun 23 years before it was found on Earth.[100]

Origin and current state

Atoms form about 4% of the total energy density of the observable universe, with an average density of about 0.25 atoms/m3.[101] Within a galaxy such as the Milky Way, atoms have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 105 to 109 atoms/m3.[102] The Sun is believed to be inside the Local Bubble, a region of highly ionized gas, so the density in the solar neighborhood is only about 103 atoms/m3.[103] Stars form from dense clouds in the ISM, and the evolutionary processes of stars result in the steady enrichment of the ISM with elements more massive than hydrogen and helium. Up to 95% of the Milky Way’s atoms are concentrated inside stars and the total mass of atoms forms about 10% of the mass of the galaxy.[104] (The remainder of the mass is an unknown dark matter.[105])

Nucleosynthesis
Main article: Nucleosynthesis

Stable protons and electrons appeared one second after the Big Bang. During the following three minutes, Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the universe, and perhaps some of the beryllium and boron.[106][107][108] The first atoms (complete with bound electrons) were theoretically created 380,000 years after the Big Bang—an epoch called recombination, when the expanding universe cooled enough to allow electrons to become attached to nuclei.[109] Since then, atomic nuclei have been combined in stars through the process of nuclear fusion to produce elements up to iron.[110]

Isotopes such as lithium-6 are generated in space through cosmic ray spallation.[111] This occurs when a high-energy proton strikes an atomic nucleus, causing large numbers of nucleons to be ejected. Elements heavier than iron were produced in supernovae through the r-process and in AGB stars through the s-process, both of which involve the capture of neutrons by atomic nuclei.[112] Elements such as lead formed largely through the radioactive decay of heavier elements.[113]

Earth

Most of the atoms that make up the Earth and its inhabitants were present in their current form in the nebula that collapsed out of a molecular cloud to form the Solar System. The rest are the result of radioactive decay, and their relative proportion can be used to determine the age of the Earth through radiometric dating.[114][115] Most of the helium in the crust of the Earth (about 99% of the helium from gas wells, as shown by its lower abundance of helium-3) is a product of alpha decay.[116]

There are a few trace atoms on Earth that were not present at the beginning (i.e., not “primordial”), nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere.[117] Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions.[118][119] Of the transuranic elements—those with atomic numbers greater than 92—only plutonium and neptunium occur naturally on Earth.[120][121] Transuranic elements have radioactive lifetimes shorter than the current age of the Earth[122] and thus identifiable quantities of these elements have long since decayed, with the exception of traces of plutonium-244 possibly deposited by cosmic dust.[114] Natural deposits of plutonium and neptunium are produced by neutron capture in uranium ore.[123]

The Earth contains approximately 1.33 × 1050 atoms.[124] In the planet’s atmosphere, small numbers of independent atoms of noble gases exist, such as argon and neon. The remaining 99% of the atmosphere is bound in the form of molecules, including carbon dioxide and diatomic oxygen and nitrogen. At the surface of the Earth, atoms combine to form various compounds, including water, salt, silicates and oxides. Atoms can also combine to create materials that do not consist of discrete molecules, including crystals and liquid or solid metals.[125][126] This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter.[127]

RMS Titanic before departing Southampton, England. photo taken Good Friday 5 April 1912
Career
Name: RMS Titanic
Owner: White Star Line
Port of Registry: Liverpool
Route: Southampton to New York City
Builder: Harland and Wolff yards in Belfast, UK
Yard number: 401
Laid down: 31 March 1909
Launched: 31 May 1911
Christened: Not christened
Completed: 31 March 1912
Maiden voyage: 10 April 1912
Identification: Radio Callsign “MGY”
UK Official Number: 131428
Fate: Sank on 15 April, 1912 after hitting an iceberg
General characteristics
Class and type: Olympic-class ocean liner
Tonnage: 46,328 gross register tons (GRT)
Displacement: 52,310 tons
Length: 882 ft 9 in (269.1 m)[1]
Beam: 92 ft 0 in (28.0 m)[1]
Height: 175 ft (53.3 m) (Keel to top of funnels)
Draught: 34 ft 7 in (10.5 m)
Depth: 64 ft 6 in (19.7 m)[1]
Decks: 9 (Lettered A through G with boilers below)
Installed power:

* 24 double-ended (six furnace) and 5 single-ended (three furnace) Scotch marine boilers
* Two four-cylinder reciprocating triple-expansion steam engines each producing 15,000 hp for the two outboard wing propellers at 75 revolutions per minute[2]
* One low-pressure turbine producing 16,000 hp[2]
* 46,000 HP (design) – 59,000 HP (maximum)[3]

Propulsion:

* Two bronze triple-blade wing propellers
* One bronze quadruple-blade centre propeller.

Speed:

* 21 knots (39 km/h; 24 mph)
* 23 knots (43 km/h; 26 mph) (maximum)

Capacity:

Passengers and crew (fully loaded):

* 3547

Staterooms (840 total):

* First Class: 416
* Second Class: 162
* Third Class: 262
* plus 40 open berthing areas

The RMS Titanic was an Olympic-class passenger liner owned by the White Star Line and built at the Harland and Wolff shipyard in Belfast, United Kingdom. For her time, she was the largest passenger steamship in the world.

On the night of 14 April 1912, during her maiden voyage, Titanic hit an iceberg and sank two hours and forty minutes later, early on 15 April 1912. The sinking resulted in the deaths of 1,517 people, making it one of the most deadly peacetime maritime disasters in history. The high casualty rate was due in part to the fact that, although complying with the regulations of the time, the ship did not carry enough lifeboats for everyone aboard. The ship had a total lifeboat capacity of 1,178 persons even though her maximum capacity was 3,547 people. A disproportionate number of men died also, due to the women-and-children-first protocol that was followed.

The Titanic used some of the most advanced technology available at the time and was, after the sinking, popularly believed to have been described as “unsinkable”.[4] It was a great shock to many that, despite the extensive safety features and experienced crew, the Titanic sank. The frenzy on the part of the media about Titanic’s famous victims, the legends about the sinking, the resulting changes to maritime law, and the discovery of the wreck have contributed to the interest in and fame of the Titanic that continues to this day.
Contents
[hide]

* 1 Construction
o 1.1 Features
o 1.2 Lifeboats
o 1.3 Comparisons with the Olympic
* 2 Ship history
o 2.1 Maiden voyage
o 2.2 Sinking
o 2.3 Lifeboats launched
o 2.4 Final minutes
* 3 Aftermath
o 3.1 Arrival of Carpathia in New York
o 3.2 Survivors, victims and statistics
o 3.3 Retrieval and burial of the dead
o 3.4 Memorials
* 4 Investigations into the RMS Titanic disaster
o 4.1 SS Californian inquiry
* 5 Rediscovery of the Titanic
o 5.1 Current condition of the wreck
o 5.2 Ownership and litigation
* 6 Possible factors in the sinking
o 6.1 Steel plates and iron rivets
o 6.2 Rudder and turning ability
o 6.3 Iceberg impact
o 6.4 Alternative theories
* 7 Legends and myths regarding the RMS Titanic
o 7.1 Unsinkable
o 7.2 David Sarnoff, wireless reports and the use of SOS
o 7.3 Titanic’s band
o 7.4 The “Titanic curse”
* 8 See also
* 9 References
o 9.1 Explanatory notes
o 9.2 Notes
o 9.3 Bibliography
* 10 External links

Construction
The first-class Grand Staircase aboard the Titanic.

The Titanic was a White Star Line ocean liner, built at the Harland and Wolff shipyard in Belfast, and designed to compete with the rival Cunard Line’s Lusitania and Mauretania. The Titanic, along with her Olympic-class sisters, the Olympic and the soon to be built Britannic, were intended to be the largest, most luxurious ships ever to operate. The designers were William Pirrie,[5] a director of both Harland and Wolff and White Star, naval architect Thomas Andrews, Harland and Wolff’s construction manager and head of their design department,[6] and Alexander Carlisle, the shipyard’s chief draughtsman and general manager.[7] Carlisle’s role in this project was the design of the superstructure of these ships, particularly the superstructures’ streamlined joining to the hulls[citation needed] as well as the implementation of an efficient lifeboat davit design. Carlisle would leave the project in 1910, before the ships were launched, when he became a shareholder in Welin Davit & Engineering Company Ltd, the firm making the davits.[8]

Construction of RMS Titanic, funded by the American J.P. Morgan and his International Mercantile Marine Co., began on 31 March, 1909. Titanic’s hull was launched on 31 May 1911, and her outfitting was completed by 31 March the following year. She was 882 feet 9 inches (269.1 m) long and 92 feet 0 inches (28.0 m) wide,[1] with a gross register tonnage of 46,328 long tons and a height from the water line to the boat deck of 59 feet (18 m). She was equipped with two reciprocating four-cylinder, triple-expansion, inverted steam engines and one low-pressure Parsons turbine, which powered three propellers. There were 29 boilers fired by 159 coal burning furnaces that made possible a top speed of 23 knots (43 km/h; 26 mph). Only three of the four 62 feet (19 m) funnels were functional: the fourth, which served only as a vent, was added to make the ship look more impressive. The ship could carry a total of 3,547 passengers and crew and, because she carried mail, her name was given the prefix RMS (Royal Mail Steamer) as well as SS (Steam Ship).

Features
Gymnasium aboard the Titanic.

In her time, Titanic surpassed all rivals in luxury and opulence. She offered an on-board swimming pool, a gymnasium, a Turkish bath, libraries in both the first and second-class, and a squash court.[9] First-class common rooms were adorned with ornate wood panelling, expensive furniture and other decorations.[10] In addition, the Café Parisien offered cuisine for the first-class passengers, with a sunlit veranda fitted with trellis decorations.[11]

The ship incorporated technologically advanced features for the period. She had an extensive electrical subsystem with steam-powered generators and ship-wide wiring feeding electric lights. She also boasted two Marconi radios, including a powerful 1,500-watt set manned by two operators working in shifts, allowing constant contact and the transmission of many passenger messages.[12] First class passengers paid a hefty fee for such amenities. The most expensive one-way trans-Atlantic passage was $4,350 (which is more than $80,000 in today’s currency).[13]

Lifeboats

At the design stage Carlisle suggested that Titanic use a new, larger type of davit which could give the ship the potential to carry 48 lifeboats; these would have provided enough places for everyone on board, but not enough for the number of people the ship could carry. However, the White Star Line, while agreeing to the larger davits, decided that only 16 wooden lifeboats (16 being the minimum allowed by the board of trade, based on the Titanic’s projected tonnage) would be carried (there were also four folding lifeboats, called collapsibles), which could accommodate only 52% of the people aboard. At the time, the Board of Trade’s regulations stated that British vessels over 10,000 tons must carry 16 lifeboats with a capacity of 5,500 cubic feet (160 m3), plus enough capacity in rafts and floats for 75% (or 50% in case of a vessel with watertight bulkheads) of that in the lifeboats. Therefore, the White Star Line actually provided more lifeboat accommodation than was legally required.[14] The regulations made no extra provision for larger ships because they had not been changed since 1894, when the largest passenger ship under consideration was only 13,000 long tons (the Cunard Line’s Lucania) and because of the expected difficulty in getting away a greater number than 16 boats in any emergency.[15] Carlisle told the official inquiry that he had discussed the matter with J. Bruce Ismay, White Star’s Managing Director, but in his evidence Ismay denied that he had ever heard of this, nor did he recollect noticing such provision in the plans of the ship he had inspected.[8][16]

Comparisons with the Olympic

The Titanic closely resembled her older sister Olympic. Although she enclosed more space and therefore had a larger gross register tonnage, the hull was almost the same length as the Olympic’s. However, there were a few differences. Two of the most noticeable were that half of the Titanics’s forward promenade A-Deck (below the boat deck) was enclosed against outside weather, and her B-Deck configuration was different from the Olympic’s. As built the Olympic did not have an equivalent of the Titanic’s Café Parisien: the feature was not added until 1913. Some of the flaws found on the Olympic, such as the creaking of the aft expansion joint, were corrected on the Titanic. The skid lights that provided natural illumination on A-deck were round, while on Olympic they were oval. The Titanic’s wheelhouse was made narrower and longer than the Olympic’s.[17] These, and other modifications, made the Titanic 1,004 gross register tons larger than the Olympic and thus the largest active ship in the world during her maiden voyage in April 1912.

Ship history

Maiden voyage
Titanic on her way after the near collision with the SS New York. On the left can be seen the Oceanic and the New York.

The vessel began her maiden voyage from Southampton, England, bound for New York City, New York, on Wednesday, 10 April 1912, with Captain Edward J. Smith in command. As the Titanic left her berth, her wake caused the liner City of New York, which was docked nearby, to break away from her moorings, whereupon she was drawn dangerously close (about four feet) to the Titanic before a tugboat towed the New York away.[18] The near accident delayed departure for one hour[citation needed]. After crossing the English Channel, the Titanic stopped at Cherbourg, France, to board additional passengers and stopped again the next day at Queenstown (known today as Cobh), Ireland. As harbour facilities at Queenstown were inadequate for a ship of her size, Titanic had to anchor off-shore, with small boats, known as tenders, ferrying the embarking passengers out to her. When she finally set out for New York, there were 2,240 people aboard.[19]

John Coffey, a 23-year-old crewmember, jumped ship by stowing away on a tender and hid amongst mailbags headed for Cobh. Coffey stated that the reason for smuggling himself off the liner was that he held a superstition about sailing and specifically about travelling on the Titanic. However, he later signed on to join the crew of the Mauretania.[20]
Captain Edward J. Smith master of the Titanic.

On the maiden voyage of the Titanic some of the most prominent people of the day were travelling in first–class. Some of these included millionaire John Jacob Astor IV and his wife Madeleine Force Astor, industrialist Benjamin Guggenheim, Macy’s owner Isidor Straus and his wife Ida, Denver millionairess Margaret “Molly” Brown, Sir Cosmo Duff Gordon and his wife couturière Lucy (Lady Duff-Gordon), George Elkins Widener and his wife Eleanor; cricketer and businessman John Borland Thayer with his wife Marian and their seventeen-year-old son Jack, journalist William Thomas Stead, the Countess of Rothes, United States presidential aide Archibald Butt, author and socialite Helen Churchill Candee, author Jacques Futrelle his wife May and their friends, Broadway producers Henry and Rene Harris and silent film actress Dorothy Gibson among others.[21] Also travelling in first–class were White Star Line’s managing director J. Bruce Ismay and the ship’s builder Thomas Andrews, who was on board to observe any problems and assess the general performance of the new ship.[21]

Sinking
Main article: Timeline of the sinking of the RMS Titanic
Route and location of the RMS Titanic.

On the night of Sunday, 14 April 1912, the temperature had dropped to near freezing and the ocean was calm. The moon was not visible and the sky was clear. Captain Smith, in response to iceberg warnings received via wireless over the preceding few days, altered the Titanic’s course slightly to the south. That Sunday at 13:45,[a] a message from the steamer Amerika warned that large icebergs lay in the Titanic’s path, but as Jack Phillips and Harold Bride, the Marconi wireless radio operators, were employed by Marconi [22] and paid to relay messages to and from the passengers,[23] they were not focused on relaying such “non-essential” ice messages to the bridge.[24] Later that evening, another report of numerous large icebergs, this time from the Mesaba, also failed to reach the bridge.

At 23:40 while sailing about 400 miles south of the Grand Banks of Newfoundland, lookouts Fredrick Fleet and Reginald Lee spotted a large iceberg directly ahead of the ship. Fleet sounded the ship’s bell three times and telephoned the bridge exclaiming, “Iceberg, right ahead!”. First Officer Murdoch gave the order “hard-a-starboard”, using the traditional tiller order for an abrupt turn to port (left), and the engines to be put in full reverse (although a survivor from the engine room testified that, as he recalled, the indicator of the telegraph had moved to “stop”, and only after the impact).[25][26] A collision was inevitable and the iceberg brushed the ship’s starboard side, buckling the hull in several places and popping out rivets below the waterline over a length of 299 feet (90 m). As seawater filled the forward compartments, the watertight doors shut. However, while the ship could stay afloat with four flooded compartments, five were filling with water. The five water-filled compartments weighed down the ship so that the tops of the forward watertight bulkheads fell below the ship’s waterline, allowing water to pour into additional compartments. Captain Smith, alerted by the jolt of the impact, arrived on the bridge and ordered a full stop. Shortly after midnight on 15 April, following an inspection by the ship’s officers and Thomas Andrews, the lifeboats were ordered to be readied and a distress call was sent out.
Photograph of an iceberg in the vicinity of the RMS Titanic’s sinking taken on 15 April 1912 by the chief steward of the liner Prinz Adelbert who stated the berg had red anti-fouling paint of the kind found on the hull from below Titanic’s waterline.

Wireless operators Jack Phillips and Harold Bride were busy sending out CQD, the international distress signal. Several ships responded, including Mount Temple, Frankfurt and Titanic’s sister ship, Olympic, but none was close enough to make it in time.[27] The closest ship to respond was Cunard Line’s Carpathia 58 miles (93 km) away, which could arrive in an estimated four hours—too late to rescue all of Titanic’s passengers. The only land–based location that received the distress call from Titanic was a wireless station at Cape Race, Newfoundland.[27]

From the bridge, the lights of a nearby ship could be seen off the port side. Not responding to wireless, Fourth Officer Boxhall and Quartermaster Rowe attempted signalling the ship with a Morse lamp and later with distress rockets, but the ship never appeared to respond.[28] The Californian, which was nearby and stopped for the night because of ice, also saw lights in the distance. The Californian’s wireless was turned off, and the wireless operator had gone to bed for the night. Just before he went to bed at around 23:00 the Californian’s radio operator attempted to warn the Titanic that there was ice ahead, but he was cut off by an exhausted Jack Phillips, who snapped, “Shut up, shut up, I am busy; I am working Cape Race”.[29] When the Californian’s officers first saw the ship, they tried signalling her with their Morse lamp, but also never appeared to receive a response. Later, they noticed the Titanic’s distress signals over the lights and informed Captain Stanley Lord. Even though there was much discussion about the mysterious ship, which to the officers on duty appeared to be moving away, the Californian did not wake her wireless operator until morning.[28]

Lifeboats launched
Sinking of the Titanic by Henry Reuterdahl, drawn based on radio descriptions.

The first lifeboat launched was Lifeboat 7 on the starboard side with 28 people on board out of a capacity of 65. It was lowered at around 00:40 as believed by the British Inquiry.[30] Lifeboat 5 was launched two to three minutes later. The Titanic carried 20 lifeboats with a total capacity of 1,178 persons. While not enough to hold all of the passengers and crew, the Titanic carried more boats than was required by the British Board of Trade Regulations. At the time, the number of lifeboats required was determined by a ship’s gross register tonnage, rather than her human capacity.

The Titanic showed no outward signs of being in imminent danger, and passengers were reluctant to leave the apparent safety of the ship to board small lifeboats. As a result, most of the boats were launched partially empty; one boat meant to hold 40 people left the Titanic with only 12 people on board it. With “Women and children first” the imperative for loading lifeboats, Second Officer Lightoller, who was loading boats on the port side, allowed men to board only if oarsmen were needed, even if there was room. First Officer Murdoch, who was loading boats on the starboard side, let men on board if women were absent. As the ship’s list increased people started to become nervous, and some lifeboats began leaving fully loaded. By 02:05, the entire bow was under water, and all the lifeboats, save for two, had been launched.

Final minutes
Survivors aboard a collapsible lifeboat.

Around 02:10, the stern rose out of the water exposing the propellers, and by 02:17 the waterline had reached the boat deck. The last two lifeboats floated off the deck, one upside down, the other half filled with water. Shortly afterwards, the forward funnel collapsed, crushing part of the bridge and people in the water. On deck, people were scrambling towards the stern or jumping overboard in hopes of reaching a lifeboat. The ship’s stern slowly rose into the air, and everything unsecured crashed towards the water. While the stern rose, the electrical system finally failed and the lights went out. Shortly afterwards, the stress on the hull caused Titanic to break apart between the last two funnels, and the bow went completely under. The stern righted itself slightly and then rose vertically. After a few moments, at 02:20, this too sank into the ocean.

Only two of the 18 launched lifeboats rescued people after the ship sank. Lifeboat 4 was close by and picked up five people, two of whom later died. Close to an hour later, lifeboat 14 went back and rescued four people, one of whom died afterwards. Other people managed to climb onto the lifeboats that floated off the deck. There were some arguments in some of the other lifeboats about going back, but many survivors were afraid of being swamped by people trying to climb into the lifeboat or being pulled down by the suction from the sinking Titanic, though it turned out that there had been very little suction.

As the ship fell into the depths, the two sections behaved very differently. The streamlined bow planed off approximately 2,000 feet (609 m) below the surface and slowed somewhat, landing relatively gently. The stern plunged violently to the ocean floor, the hull being torn apart along the way from massive implosions caused by compression of the air still trapped inside. The stern smashed into the bottom at considerable speed, grinding the hull deep into the silt.

After steaming under a forced draft for just under four hours, the RMS Carpathia arrived in the area and at 04:10 began rescuing survivors. By 08:30 she picked up the last lifeboat with survivors and left the area at 08:50 bound for New York.[31]

Aftermath

Arrival of Carpathia in New York
Carpathia docked at Pier 54 in New York following the rescue.

On 18 April, the Carpathia docked at Pier 54 at Little West 12th Street in New York with the survivors. It arrived at night and was greeted by thousands of people. The Titanic had been headed for 20th Street. The Carpathia dropped off the empty Titanic lifeboats at Pier 59, as property of the White Star Line, before unloading the survivors at Pier 54. Both piers were part of the Chelsea Piers built to handle luxury liners of the day. As news of the disaster spread, many people were shocked that the Titanic could sink with such great loss of life despite all of her technological advances. Newspapers were filled with stories and descriptions of the disaster and were eager to get the latest information. Many charities were set up to help the victims and their families, many of whom lost their sole breadwinner, or, in the case of third-class survivors, lost everything they owned.[32] The people of Southampton were deeply affected by the sinking. According to the Hampshire Chronicle on 20 April 1912, almost 1,000 local families were directly affected. Almost every street in the Chapel district of the town lost more than one resident and over 500 households lost a member.[33]

Survivors, victims and statistics
See also: Maritime disasters, List of passengers on board RMS Titanic, and List of crew members on board RMS Titanic
Category Number Aboard Number of Survivors Percentage That Survived Number Lost Percentage That Were Lost
First Class 329 199 60.5 % 130 39.5 %
Second Class 285 119 41.7 % 166 58.3 %
Third Class 710 174 24.5 % 536 75.5 %
Crew 899 214 23.8 % 685 76.2 %
Total 2,223 706 31.8 % 1,517 68.2 %
New York Herald front page about the Titanic disaster.

Of a total of 2,223 people aboard the Titanic only 706 survived the disaster and 1,517 perished.[34] The majority of deaths were caused by hypothermia in the 28 °F (−2 °C) water. Men and members of the lower classes were less likely to survive. 92 percent of the men perished in second class. Third class passengers fared very badly.

Six of the seven children in first class and all of the children in second class were saved, whereas only 34 percent were saved in third class. Nearly every first-class woman survived, compared with 86 percent of those in second class and less than half of those in third class. Over all, only 20 percent of the men survived, compared to nearly 75 percent of the women. First-class men were four times as likely to survive as second-class men, and twice as likely to survive as third-class men.[35]

Another disparity is that a greater percentage of British passengers died than American passengers, some sources claim this could be because many Britons of the time were too polite to force their way onto the lifeboats.[36]

* In one case in the third class, a Swedish family lost the mother, Alma Pålsson, and her four children, all aged under 10. The father was waiting for them to arrive at the destination. “Paulson’s grief was the most acute of any who visited the offices of the White Star, but his loss was the greatest. His whole family had been wiped out.”[37]
* The sailors aboard the ship CS Mackay-Bennett which recovered bodies from Titanic, who were very upset by the discovery of the unknown boy’s body, paid for a monument and he was buried on 4 May 1912 with a copper pendant placed in his coffin by the sailors that read “Our Babe”. The unknown child was later positively identified as Sidney Goodwin.
* One survivor, stewardess Violet Jessop, who had been on board the RMS Olympic when she collided with HMS Hawke in 1911, went on to survive the sinking of HMHS Britannic in 1916.
* Titanic survivors who have recently passed away include Lillian Asplund on 6 May 2006 and Barbara Dainton (née West) on 16 October 2007.
* Millvina Dean, who was only two months old at the time of the sinking, is the only living survivor of the Titanic. Although she is 97 years old, she has remained active in Titanic-related events and lives in Southampton, England.
* There are many stories relating to dogs on the Titanic. Apparently, a passenger released the dogs just before the ship went down; they were seen running up and down the decks. At least two dogs survived.[38]

Retrieval and burial of the dead
Marker of the unknown child who was later positively identified as Sidney Leslie Goodwin.

Once the massive loss of life became clear, White Star Line chartered the cable ship CS Mackay-Bennett from Halifax, Nova Scotia to retrieve bodies. Three other ships followed in the search, the cable ship Minia, the lighthouse supply ship Montmagny and the sealing vessel Algerine. Each ship left with embalming supplies, undertakers, and clergy. Of the 333 victims that were eventually recovered, 328 were retrieved by the Canadian ships and five more by passing North Atlantic steamships. For some unknown reason, numbers 324 and 325 were unused, and the six passengers buried at sea by the Carpathia also went unnumbered.[39] In mid-May 1912, over 200 miles (320 km) from the site of the sinking the Oceanic, recovered three bodies, numbers 331, 332 and 333, who were occupants of Collapsible A, which was swamped in the last moments of the sinking. Several people managed to reach this lifeboat, although some died during the night. When Fifth Officer Harold Lowe rescued the survivors of Collapsible A, he left the three dead bodies in the boat: Thomas Beattie, a first-class passenger, and two crew members, a fireman and a seaman. The bodies were buried at sea from Oceanic.[40]

The first body recovery ship to reach the site of the sinking, the cable ship CS Mackay-Bennett found so many bodies that the embalming supplies aboard were quickly exhausted. Health regulations only permitted that embalmed bodies could be returned to port.[41] Captain Larnder of the Mackay-Bennett and undertakers aboard decided to preserve all bodies of First Class passengers, justifying their decision by the need to visually identify wealthy men to resolve any disputes over large estates. As a result the burials at sea were Third Class passengers and crew. Larnder himself claimed that as a mariner, he would expect to be buried at sea.[42] However complaints about the burials at sea were made by families and undertakers. Later ships such as Minia found fewer bodies, requiring fewer embalming supplies, and were able to limit burials at sea to bodies which were too damaged to preserve.

Bodies recovered were preserved to be taken to Halifax, the closest city to the sinking with direct rail and steamship connections. The Halifax coroner, John Henry Barnstead, developed a detailed system to identify bodies and safeguard personal possessions. His identification system would later be used to identify victims of the Halifax Explosion in 1917. Relatives from across North America came to identify and claim bodies. A large temporary morgue was set up in a curling rink and undertakers were called in from all across Eastern Canada to assist.[40] Some bodies were shipped to be buried in their hometowns across North America and Europe. About two thirds of the bodies were identified. Unidentified victims were buried with simple numbers based on the order that the bodies were discovered. The majority of recovered victims, 150 bodies, were buried in three Halifax cemeteries, the largest being Fairview Lawn Cemetery followed by the nearby Mount Olivet and Baron de Hirsch cemeteries.[43] Much floating wreckage was also recovered with the bodies, many pieces of which can be seen today in the Maritime Museum of the Atlantic in Halifax.

Memorials
The Anna Bliss Titanic Victims Memorial in Woodlawn Cemetery
The memorial to the Titanic’s engineers in Southampton

In many locations there are memorials to the dead of the Titanic. In Southampton, England a memorial to the engineers of the Titanic may be found in Andrews Park on Above Bar Street. Opposite the main memorial is a memorial to Wallace Hartley and the other musicians who played on the Titanic. A memorial to the liner is also located on the grounds of City Hall in Belfast, Northern Ireland.

In the United States there are memorials to the Titanic disaster as well. The Titanic Memorial in Washington, D.C. and a memorial to Ida Straus at Straus Park in Manhattan, New York are two examples.

On 15 April 2012, the 100th anniversary of the sinking of Titanic is planned to be commemorated around the world. By that date, the Titanic Quarter in Belfast is planned to have been completed. The area will be regenerated and a signature memorial project unveiled to celebrate Titanic and her links with Belfast, the city that had built the ship.[44]

Investigations into the RMS Titanic disaster
See also: Changes in safety practices following the RMS Titanic disaster and International Maritime Organization
Political cartoon from 1912 which shows the public demanding answers from the shipping companies about the Titanic disaster

Before the survivors even arrived in New York, investigations were being planned to discover what had happened, and what could be done to prevent a recurrence. The United States Senate initiated an inquiry into the disaster on 19 April, a day after Carpathia arrived in New York.

The chairman of the inquiry, Senator William Alden Smith, wanted to gather accounts from passengers and crew while the events were still fresh in their minds. Smith also needed to subpoena the British citizens while they were still on American soil. This prevented all surviving passengers and crew from returning to England before the American inquiry, which lasted until 25 May, was completed.

Lord Mersey was appointed to head the British Board of Trade’s inquiry into the disaster. The British inquiry took place between 2 May and 3 July. Each inquiry took testimony from both passengers and crew of the Titanic, crew members of Leyland Line’s Californian, Captain Arthur Rostron of the Carpathia and other experts.

The investigations found that many safety rules were simply out of date, and new laws were recommended. Numerous safety improvements for ocean-going vessels were implemented, including improved hull and bulkhead design, access throughout the ship for egress of passengers, lifeboat requirements, improved life-vest design, the holding of safety drills, better passenger notification, radio communications laws, etc. The investigators also learned that the Titanic had sufficient lifeboat space for all first-class passengers, but not for the lower classes. In fact, most third-class, or steerage, passengers had no idea where the lifeboats were, much less any way of getting up to the higher decks where the lifeboats were stowed.

SS Californian inquiry
The SS Californian.

Both inquiries into the disaster found that the SS Californian and its captain, Stanley Lord, failed to give proper assistance to the Titanic. Testimony before the inquiry revealed that at 22:10, the Californian observed the lights of a ship to the south; it was later agreed between Captain Lord and Third Officer C.V. Groves (who had relieved Lord of duty at 22:10) that this was a passenger liner. The Californian warned the ship by radio of the pack ice because of which the Californian had stopped for the night, but was violently rebuked by Titanic senior wireless operator, Jack Phillips. At 23:50, the officer had watched this ship’s lights flash out, as if the ship had shut down or turned sharply, and that the port light was now observed. Morse light signals to the ship, upon Lord’s order, occurred five times between 23:30 and 01:00, but were not acknowledged. (In testimony, it was stated that the Californian’s Morse lamp had a range of about four miles (6 km), so could not have been seen from Titanic.)[28]

Captain Lord had retired at 23:30; however, Second Officer Herbert Stone, now on duty, notified Lord at 01:15 that the ship had fired a rocket, followed by four more. Lord wanted to know if they were company signals, that is, coloured flares used for identification. Stone said that he did not know that the rockets were all white. Captain Lord instructed the crew to continue to signal the other vessel with the Morse lamp, and went back to sleep. Three more rockets were observed at 1:50 and Stone noted that the ship looked strange in the water, as if she were listing. At 02:15, Lord was notified that the ship could no longer be seen. Lord asked again if the lights had had any colours in them, and he was informed that they were all white.

The Californian eventually responded. At 05:30, Chief Officer George Stewart awakened wireless operator Cyril Evans, informed him that rockets had been seen during the night, and asked that he try to communicate with any ships. The Frankfurt notified the operator of the Titanic’s loss, Captain Lord was notified, and the ship set out for assistance.

The inquiries found that the Californian was much closer to the Titanic than the 19.5 miles (31.38 km) that Captain Lord had believed and that Lord should have awakened the wireless operator after the rockets were first reported to him, and thus could have acted to prevent a loss of life.[28]

In 1990, following the discovery of the wreck, the Marine Accident Investigation Branch of the British Department of Transport re-opened the inquiry to review the evidence relating to the Californian. Its report of 1992 concluded that the Californian was farther from the Titanic than the earlier British inquiry had found, and that the distress rockets, but not the Titanic herself, would have been visible from the Californian.[45]

Rediscovery of the Titanic
See also: List of shipwrecks
Titanic’s bow, with the forestay shackle fallen forwards, as seen from the Russian MIR I submersible.

The idea of finding the wreck of Titanic, and even raising the ship from the ocean floor, had been around since shortly after the ship sank. No attempts were successful until September 1,1985, when a joint American-French expedition, led by Jean-Louis Michel (Ifremer) and Dr. Robert Ballard (WHOI), located the wreck using the side-scan sonar from the research vessel Knorr. It was found at a depth of 2.5 miles (4.02 km), slightly more than 370 miles (595.46 km) south-east of Mistaken Point, Newfoundland at [show location on an interactive map] 41°43′55″N 49°56′45″W / 41.73194°N 49.94583°W / 41.73194; -49.94583Coordinates: [show location on an interactive map] 41°43′55″N 49°56′45″W / 41.73194°N 49.94583°W / 41.73194; -49.94583, 13 miles (20.92 km) from fourth officer Joseph Boxhall’s last position reading where Titanic was originally thought to rest. Ballard noted that his crew had paid out 12,500 feet (3,810 m) of the sonar’s tow cable at the time of the discovery of the wreck,[46] giving an approximate depth of the seabed of 12,450 feet (3,795 m).[47] Ifremer, the French partner in the search, records a depth of 3,800 m (12,467 ft), an almost exact equivalent.[48] This approximates to 2.33 miles (3.75 km), often rounded upwards to 2.5 miles (4.02 km). In 1986 Ballard returned to the wreck site aboard the Atlantis II to conduct the first manned dives to the wreck in the submersible Alvin.

Ballard had in 1982 requested funding for the project from the US Navy, but this was provided only on the condition that the first priority was the search for the sunken US submarines Thresher and Scorpion. Only when these had been discovered and photographed did the search for Titanic begin.[49]

The most notable discovery the team made was that the ship had split apart, the stern section lying 1,970 feet (600 m) from the bow section and facing opposite directions. There had been conflicting witness accounts of whether the ship broke apart or not, and both the American and British inquiries found that the ship sank intact. Up until the discovery of the wreck, it was generally assumed that the ship did not break apart.

The bow section had struck the ocean floor at a position just under the forepeak, and embedded itself 60 feet (18 m) into the silt on the ocean floor. Although parts of the hull had buckled, the bow was mostly intact. The collision with the ocean floor forced water out of Titanic through the hull below the well deck. One of the steel covers (reportedly weighing approximately ten tonnes) was blown off the side of the hull. The bow is still under tension, in particular the heavily damaged and partially collapsed decks.[50]

The stern section was in much worse condition, and appeared to have been torn apart during its descent. Unlike the bow section, which was flooded with water before it sank, it is likely that the stern section sank with a significant volume of air trapped inside it. As it sank, the external water pressure increased but the pressure of the trapped air could not follow suit due to the many air pockets in relatively sealed sections. Therefore, some areas of the stern section’s hull experienced a large pressure differential between outside and inside which possibly caused an implosion. Further damage was caused by the sudden impact of hitting the seabed; with little structural integrity left, the decks collapsed as the stern hit.[51]

Surrounding the wreck is a large debris field with pieces of the ship, furniture, dinnerware and personal items scattered over one square mile (2.6 km²). Softer materials, like wood, carpet and human remains were devoured by undersea organisms.

Dr. Ballard and his team did not bring up any artefacts from the site, considering this to be tantamount to grave robbing. Under international maritime law, however, the recovery of artefacts is necessary to establish salvage rights to a shipwreck. In the years after the find, Titanic has been the object of a number of court cases concerning ownership of artefacts and the wreck site itself. In 1994, RMS Titanic Inc. was awarded ownership and salvaging rights of the wreck, even though RMS Titanic Inc. and other salvaging expeditions have been criticized for taking items from the wreck. Among the items recovered by RMS Titanic Inc. was the ship’s whistle, which was brought to the surface in 1992 and placed in the company’s travelling exhibition. It has been operated only twice since, using compressed air rather than steam, because of its fragility.[52]

Approximately 6,000 artefacts have been removed from the wreck. Many of these were put on display at the National Maritime Museum in Greenwich, England, and later as part of a travelling museum exhibit.

Current condition of the wreck
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Many scientists, including Robert Ballard, are concerned that visits by tourists in submersibles and the recovery of artefacts are hastening the decay of the wreck. Underwater microbes have been eating away at Titanic’s iron since the ship sank, but because of the extra damage visitors have caused the National Oceanic and Atmospheric Administration estimates that “the hull and structure of the ship may collapse to the ocean floor within the next 50 years.”

Ballard’s book Return to Titanic, published by the National Geographic Society, includes photographs depicting the deterioration of the promenade deck and damage caused by submersibles landing on the ship. The mast has almost completely deteriorated and has been stripped of its bell and brass light. Other damage includes a gash on the bow section where block letters once spelled Titanic, part of the brass telemotor which once held the ship’s wooden wheel is now twisted and the crows nest has now completely deteriorated.

Ownership and litigation

Titanic’s rediscovery in 1985 launched a debate over ownership of the wreck and the valuable items inside. On 7 June 1994 RMS Titanic Inc., a subsidiary of Premier Exhibitions Inc., was awarded ownership and salvaging rights by the United States District Court for the Eastern District of Virginia.[53] (See Admiralty law)[54] Since 1987, RMS Titanic Inc. and its predecessors have conducted seven expeditions and salvaged over 5,500 historic objects. The biggest single recovered object was a 17-ton section of the hull, recovered in 1998.[55] Many of these items are part of travelling museum exhibitions.

In 1993, a French administrator in the Office of Maritime Affairs of the Ministry of Equipment, Transportation, and Tourism awarded RMS Titanic Inc.’s predecessor title to the relics recovered in 1987.

In a motion filed on 12 February 2004, RMS Titanic Inc. requested that the district court enter an order awarding it “title to all the artifacts (including portions of the hull) which are the subject of this action pursuant to the Law of Finds” or, in the alternative, a salvage award in the amount of $225 million. RMS Titanic Inc. excluded from its motion any claim for an award of title to the objects recovered in 1987, but it did request that the district court declare that, based on the French administrative action, “the artifacts raised during the 1987 expedition are independently owned by RMST.” Following a hearing, the district court entered an order dated 2 July 2004, in which it refused to grant comity and recognize the 1993 decision of the French administrator, and rejected RMS Titanic Inc.’s claim that it should be awarded title to the items recovered since 1993 under the Maritime Law of Finds.

RMS Titanic Inc. appealed to the United States Court of Appeals for the Fourth Circuit. In its decision of 31 January 2006[56] the court recognized “explicitly the appropriateness of applying maritime salvage law to historic wrecks such as that of Titanic” and denied the application of the Maritime Law of Finds. The court also ruled that the district court lacked jurisdiction over the “1987 artifacts”, and therefore vacated that part of the court’s 2 July 2004 order. In other words, according to this decision, RMS Titanic Inc. has ownership title to the objects awarded in the French decision (valued $16.5 million earlier) and continues to be salver-in-possession of the Titanic wreck. The Court of Appeals remanded the case to the District Court to determine the salvage award ($225 million requested by RMS Titanic Inc.).[57]

Possible factors in the sinking
The iceberg buckled Titanic’s hull allowing water to flow into the ship

Originally, historians thought the iceberg had cut a gash into Titanic’s hull. Since the part of the ship that the iceberg damaged is now buried, scientists used sonar to examine the area and discovered the iceberg had caused the hull to buckle, allowing water to enter Titanic between her steel plates.

Steel plates and iron rivets

A detailed analysis of small pieces of the steel plating from the Titanic’s wreck hull found that it was of a metallurgy that loses its elasticity and becomes brittle in cold or icy water, leaving it vulnerable to dent-induced ruptures. The pieces of steel were found to have very high content of phosphorus and sulphur (4x and 2x respectively, compared to modern steel), with manganese-sulphur ratio of 6.8:1 (compare with over 200:1 ratio for modern steels). High content of phosphorus initiates fractures, sulphur forms grains of iron sulphide that facilitate propagation of cracks, and lack of manganese makes the steel less ductile. The recovered samples were found to be undergoing ductile-brittle transition in temperatures of 90 °F (32 °C) (for longitudinal samples) and 133 °F (56 °C) (for transversal samples—compare with transition temperature of -17 °F [-27 °C] common for modern steels—modern steel would become so brittle in between -76 and -94 °F [-60 and -70 °C]). The anisotropy was likely caused by hot rolling influencing the orientation of the sulphide stringer inclusions. The steel was probably produced in the acid-lined, open-hearth furnaces in Glasgow, which would explain the high content of phosphorus and sulphur, even for the time.[58][59]

Another factor was the rivets holding the hull together, which were much more fragile than once thought.[58][60] From 48 rivets recovered from the hulk of the Titanic, scientists found many to be riddled with high concentrations of slag. A glassy residue of smelting, slag can make rivets brittle and prone to fracture. Records from the archive of the builder show that the ship’s builder ordered No. 3 iron bar, known as “best” — not No. 4, known as “best-best,” for its rivets, although shipbuilders at that time typically used No. 4 iron for rivets. The company also had shortages of skilled riveters, particularly important for hand riveting, which took great skill: the iron had to be heated to a precise colour and shaped by the right combination of hammer blows. The company used steel rivets, which were stronger and could be installed by machine, on the central hull, where stresses were expected to be greatest, using iron rivets for the stern and bow.[58] Rivets of “best best” iron had a tensile strength approximately 80% of that of steel, “best” iron some 73%.[61]

Rudder and turning ability
View of the stern and rudder of one of the Olympic-class ships in dry-dock.

Although Titanic’s rudder met the mandated dimensional requirements for a ship her size, the rudder’s design was hardly state-of-the-art. According to research by BBC History: “Her stern, with its high graceful counter and long thin rudder, was an exact copy of an 18th-century sailing ship…a perfect example of the lack of technical development. Compared with the rudder design of the Cunarders, Titanic’s was a fraction of the size. No account was made for advances in scale and little thought was given to how a ship, 852 feet in length, [sic] might turn in an emergency or avoid collision with an iceberg. This was Titanic’s Achilles heel.”[62] A more objective assessment of the rudder provision compares it with the legal requirement of the time: the area had to be within a range of 1.5% and 5% of the hull’s underwater profile and, at 1.9%, the Titanic was at the low end of the range. However, the tall rudder design was more effective at the vessel’s designed cruising speed; short, square rudders were more suitable for low-speed manoeuvring.[63]

Perhaps more fatal to the design of the Titanic was her triple screw engine configuration, which had reciprocating steam engines driving her wing propellers, and a steam turbine driving her centre propeller. The reciprocating engines were reversible, while the turbine was not. According to subsequent evidence from Fourth Officer Joseph Boxhall, who entered the bridge just after the collision, First Officer Murdoch had set the engine room telegraph to reverse the engines to avoid the iceberg,[25] thus handicapping the turning ability of the ship. Because the centre turbine could not reverse during the “full speed astern” manoeuvre, it was simply stopped. Since the centre propeller was positioned forward of the ship’s rudder, the effectiveness of that rudder would have been greatly reduced: had Murdoch simply turned the ship while maintaining her forward speed, the Titanic might have missed the iceberg with metres to spare.[64] Another survivor, greaser Frederick Scott, gave contrary evidence: he recalled that at his station in the engine room all four sets of telegraphs had changed to “Stop”, but not until after the collision.[26]

Iceberg impact

It has been speculated that the ship could have been saved if she had rammed the iceberg head on.[65][66] It is hypothesised that if Titanic had not altered her course at all and instead collided head first with the iceberg, the impact would have been taken by the naturally stronger bow of the hull and damage would only have affected the first or, at most, first two compartments. This would have disabled her severely, and possibly caused casualties among the passengers near the front of the ship, but would not likely have resulted in sinking since Titanic was designed to float with the first four compartments flooded. Instead, the glancing blow to the starboard side of the ship caused buckling in the hull plates along the first five compartments, more than the ship’s designers had allowed for.

Alternative theories
Main article: Titanic alternative theories

A number of alternative theories diverging from the standard explanation for the Titanic’s demise have been brought forth since shortly after the sinking. Some of these include a coal fire aboard ship,[67] or the Titanic hitting pack ice rather than an iceberg.[68][69] Also, the notion has been advanced that it was the White Star Lines’ nearly identical ship, Olympic, and not Titanic that was sunk as part of an insurance scam.[70] In the realm of the supernatural, it has been proposed that the Titanic sank due to a mummy’s curse.[71]

Legends and myths regarding the RMS Titanic

Unsinkable

Contrary to popular mythology, the Titanic was never described as “unsinkable”, without qualification, until after she sank.[4][72] There are three trade publications (one of which was probably never published) that describe the Titanic as unsinkable, prior to its sinking, but they all qualify the claim, either with the word practically or with the phrase as far as possible. There is no evidence that the notion of the Titanic’s unsinkability had entered public consciousness until after the sinking.[4]

The first unqualified assertion of the Titanic’s unsinkability appears the day after the tragedy (on 16 April 1912) in The New York Times, which quotes Philip A. S. Franklin, vice president of the White Star Line as saying, when informed of the tragedy,

I thought her unsinkable and I based by [sic] opinion on the best expert advice available. I do not understand it.[73]

This comment was seized upon by the press and the idea that the White Star Line had previously declared the Titanic to be unsinkable (without qualification) gained immediate and widespread currency.
David Sarnoff, wireless reports and the use of SOS

An often-quoted story that has been blurred between fact and fiction states that the first person to receive news of the sinking was David Sarnoff, who would later found media giant RCA. In modified versions of this legend, Sarnoff was not the first to hear the news (though Sarnoff willingly promoted this notion), but he and others did staff the Marconi wireless station (telegraph) atop the Wanamaker Department Store in New York City, and for three days, relayed news of the disaster and names of survivors to people waiting outside. However, even this version lacks support in contemporary accounts. No newspapers of the time, for example, mention Sarnoff. Given the absence of primary evidence, the story of Sarnoff should be properly regarded as a legend.[74][75][76][77][78]

Despite popular belief, the sinking of Titanic was not the first time the internationally recognised Morse code distress signal “SOS” was used. The SOS signal was first proposed at the International Conference on Wireless Communication at Sea in Berlin in 1906. It was ratified by the international community in 1908 and had been in widespread use since then. The SOS signal was, however, rarely used by British wireless operators, who preferred the older CQD code. First Wireless Operator Jack Phillips began transmitting CQD until Second Wireless Operator Harold Bride suggested half jokingly, “Send SOS; it’s the new call, and this may be your last chance to send it.” Phillips, who later died, then began to intersperse SOS with the traditional CQD call.

Titanic’s band
Members of the Titanic’s band.

One of the most famous stories of Titanic is of the band. On 15 April Titanic’s eight-member band, led by Wallace Hartley, had assembled in the first-class lounge in an effort to keep passengers calm and upbeat. Later they moved on to the forward half of the boat deck. The band continued playing music even when it became apparent the ship was going to sink.

None of the band members survived the sinking, and there has been much speculation about what their last song was. A first-class Canadian passenger, Mrs. Vera Dick, alleged that the final song played was the hymn “Nearer, My God, to Thee.” Hartley reportedly said to a friend if he was on a sinking ship “Nearer, My God, to Thee” would be one of the songs he would play. But Walter Lord’s book A Night to Remember popularised wireless operator Harold Bride’s account that he heard the song “Autumn” before the ship sank. It is considered Bride either meant the hymn called “Autumn” or “Songe d’Automne,” a popular song at the time. Bride is the only witness who was close enough to the band, at the moment the ship went down, to be considered reliable—Mrs. Dick had left by lifeboat an hour and 20 minutes earlier and could not possibly have heard the band’s final moments. The notion that the band played “Nearer, My God, to Thee” as their swan song, is probably a myth originating from the wrecking of the SS Valencia, which had received wide press coverage in Canada in 1906 and so may have influenced Mrs. Dick’s recollection.[4] It should also be noted that there are two different musical settings for “Nearer, My God, to Thee.” One is popular in Britain, and the other is popular in the United States, and they are not similar. The film A Night to Remember, made in 1958, uses the British setting, while the 1953 film, Titanic, with Clifton Webb, uses the American setting.

The “Titanic curse”

When Titanic sank, claims were made that a curse existed on the ship. The press quickly linked the “Titanic curse” with the White Star Line practice of not christening their ships (notwithstanding the opening scene of the film, A Night to Remember).[4]

One of the most widely spread legends linked directly into the sectarianism of the city of Belfast, where the ship was built. It was suggested that the ship was given the number 390904 which, when read backwards as reflected by the water’s surface, was claimed to spell ‘no pope’, a sectarian slogan attacking Roman Catholics that was (and is) widely used provocatively by extreme Protestants in Northern Ireland, where the ship was built. In the extreme sectarianism of north-east Ireland (Northern Ireland itself did not exist until 1920), the ship’s sinking, though mourned, was alleged to be on account of the sectarian anti-Catholicism of her manufacturers, the Harland and Wolff company, which had an almost exclusively Protestant workforce and an alleged record of hostility towards Catholics. (Harland and Wolff did have a record of hiring few Catholics; whether that was through policy or because the company’s shipyard in Belfast’s bay was located in almost exclusively Protestant East Belfast — through which few Catholics would dare to travel — or a mixture of both, is a matter of dispute.)[79]

The ‘no pope’ story is in fact an urban legend, with no basis in fact. RMS Olympic and Titanic were assigned the yard numbers 400 and 401[80] respectively. The source of the story may have been from reports by dockworkers in Queenstown (Cobh) of anti-Catholic graffiti that they found on Titanic’s coalbunkers when they were loading coal.