A neutron bomb or enhanced radiation weapon (ERW) or weapon of reinforced radiation is a type of thermonuclear weapon designed specifically to release a large portion of its energy as energetic neutron radiation rather than explosive energy. Although their extreme blast and heat effects are not eliminated, it is the enormous radiation released by ERWs that is meant to be a major source of casualties. The levels of neutron radiation released are able to penetrate through thick, protective materials such as armor, making them useful as an anti-tank weapon.[1]
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A neutron bomb is a fission-fusion thermonuclear weapon (hydrogen bomb) in which the burst of neutrons generated by a fusion reaction is intentionally allowed to escape the weapon, rather than being absorbed by its other components. The weapon's X-ray mirrors and radiation case, made of uranium or lead in a standard bomb, are instead made of chromium or nickel so that the neutrons can escape. The bombs also require amounts of tritium on the order of a few tens of grams.[2]
The "usual" nuclear weapon yield—expressed as kT TNT equivalent—is not a measure of a neutron weapon's destructive power. It refers only to the energy released (mostly heat and blast), and does not express the lethal effect of neutron radiation on living organisms. Compared to a fission bomb with the identical explosive yield, a neutron bomb would emit about ten times[3] the amount of neutron radiation. In a fission bomb, radiation pulse energy is approximately 5% of entire energy released; in the neutron bomb it would be closer to 50%. Neutron bombs release a much higher amount of neutrons than a fission bomb of the same explosive yield. Furthermore, these neutrons are of much higher energy (14 MeV) than those released during a fission reaction (1-2 MeV).[4]
Conception of the neutron bomb is generally credited to Samuel T. Cohen of the Lawrence Livermore National Laboratory, who developed the concept in 1958.[5] Testing was authorized and carried out in 1963 at an underground Nevada test facility.[6] Development was subsequently postponed by President Jimmy Carter in 1978 following protests against his administration's plans to deploy neutron warheads in Europe. President Ronald Reagan restarted production in 1981.[7]
Three types of ERW were built by the United States.[8] The W66 warhead, for the anti-ICBM Sprint missile system, was deployed in 1975 and retired the next year, along with the missile system. The W70 Mod 3 warhead was developed for the short-range, tactical Lance missile, and the W79 Mod 0 was developed for artillery shells. The latter two types were retired by President George H. W. Bush in 1992, following the end of the Cold War.[9][10] The last W70 Mod 3 warhead was dismantled in 1996,[11] and the last W79 Mod 0 was dismantled by 2003, when the dismantling of all W79 variants was completed.[12]
Besides the United States and Soviet Union, France and China are understood to have tested neutron or enhanced radiation bombs in the past, with France apparently leading the field with an early test of the technology in 1967[13] and an "actual" neutron bomb in 1980.[14] The 1999 Cox Report indicates that China is able to produce neutron bombs,[15] although no country is currently known to deploy them.
Considerable controversy arose in the U.S. and Western Europe, following a June 1977 Washington Post exposé describing U.S. government plans to purchase the bomb. The article focused on the fact that it was the first weapon specifically intended to kill humans with radiation.[16][17] Lawrence Livermore National Laboratory director Harold Brown and Soviet General Secretary Leonid Brezhnev both described the neutron bomb as a "capitalist bomb", because it was designed to destroy people while preserving property.[18][19]
Neutron bombs are purposely designed with explosive yields lower than other nuclear weapons. This is because neutrons are absorbed by air, so a high-yield neutron bomb is not able to radiate neutrons beyond its blast range and so would have no destructive advantage over a normal hydrogen bomb. This intense pulse of high-energy neutrons is intended as the principal killing mechanism, not the fallout, heat or blast. Although neutron bombs are commonly believed to "leave the infrastructure intact", current designs have explosive yields in the kiloton range,[20] the detonation of which would cause considerable destruction through blast and heat effects.
Neutron bombs could be used as strategic anti-ballistic missile weapons or as tactical weapons intended for use against armored forces. The neutron bomb was originally conceived by the U.S. military as a weapon that could stop Soviet troops from overrunning allied nations without destroying the infrastructure of the allied nation.[21]
One of the uses for which this weapon was conceived is large-scale anti-tank weaponry. Armored fighting vehicles offer a relatively high degree of protection against heat and blast, the primary destructive mechanisms of normal nuclear weapons. That is, military personnel inside a tank can be expected to survive an "ordinary" nuclear explosion at relatively close range, while the vehicle's nuclear/biological/chemical protection systems ensure a high degree of operability even in a nuclear fallout environment.
ER weapons are meant to kill a much higher percentage of enemy personnel inside such protected environments through the release of a higher percentage of their yield in the form of neutron ionizing radiation, against which tank armors, excluding depleted uranium, are ineffective.
The questionable effectiveness of ER weapons against modern tanks is cited as one of the main reasons why these weapons are no longer fielded or stockpiled. With the increase in average tank armor thickness since the first ER weapons were fielded, tank armor protection approaches the level where tank crews are now almost completely protected from radiation effects. Therefore for an ER weapon to incapacitate a modern tank crew through irradiation,[22] the weapon must now be detonated at such a close proximity to the tank that the nuclear explosion's blast would now be equally effective at incapacitating it and its crew.[23]
As an anti-ballistic missile weapon, an ER warhead was developed for the Sprint missile system as part of the Safeguard Program to protect United States cities and missile silos from incoming Soviet warheads by damaging their electronic components with the intense neutron flux.