View source for Neutron bomb

{{short description|Low-yield thermonuclear weapon}}
{| class="wikitable floatright"  style="text-align:center;"
|+ Energy distribution of weapon
|-
! rowspan=2 | Energy type
! colspan=2 | Proportion of total energy (%)
|-
! [[Nuclear fission|Fission]]
! Enhanced
|-
|Blast||50||40<ref name="news.bbc.co.uk">{{cite web |url=http://news.bbc.co.uk/2/hi/science/nature/395689.stm |title=Sci/Tech Neutron bomb: Why 'clean' is deadly |url-status=live |archive-url=https://web.archive.org/web/20111021100653/http://news.bbc.co.uk/2/hi/science/nature/395689.stm |archive-date=2011-10-21 }}</ref> to minimum 30<ref name="fas.org">{{cite web |url=https://www.fas.org/nuke/guide/usa/doctrine/dod/fm8-9/1ch2.htm |title=Chapter 2 Conventional and Nuclear Weapons - Energy Production and Atomic Physics Section I - General. Figure 2-IX, Table 2-III |url-status=live |archive-url=https://web.archive.org/web/20140719221658/http://fas.org/nuke/guide/usa/doctrine/dod/fm8-9/1ch2.htm |archive-date=2014-07-19 }}</ref>
|-
|Thermal energy||35||25<ref name="news.bbc.co.uk"/> to minimum 20<ref name="fas.org"/>
|-
|[[Prompt neutron|Prompt radiation]]||5||45 to minimum 30<ref name="news.bbc.co.uk"/>
|-
|Residual radiation||10||5<ref name="news.bbc.co.uk"/>
|}

A '''neutron bomb''', officially defined as a type of '''enhanced radiation weapon''' ('''ERW'''), is a low-yield [[thermonuclear weapon]] designed to maximize lethal [[neutron radiation]] in the immediate vicinity of the blast while minimizing the physical power of the blast itself. The neutron release generated by a [[nuclear fusion]] reaction is intentionally allowed to escape the weapon, rather than being absorbed by its other components.<ref name="The Neutron Bomb">{{cite web |url=http://www.atomicarchive.com/Fusion/Fusion5.shtml |title=The Neutron Bomb |url-status=dead |archive-url=https://web.archive.org/web/20180103000020/http://www.atomicarchive.com/Fusion/Fusion5.shtml |archive-date=2018-01-03 |access-date=2014-03-03 }}</ref> The neutron burst, which is used as the primary destructive action of the warhead, is able to penetrate enemy armor more effectively than a conventional warhead, thus making it more lethal as a tactical weapon.

The concept was originally developed by the United States in the late 1950s and early 1960s. It was seen as a "cleaner" bomb for use against massed [[Soviet Union|Soviet]] armored divisions. As these would be used over allied nations, notably [[West Germany]], the reduced blast damage was seen as an important advantage.<ref name="waynebiddle.com">{{cite web |url=http://waynebiddle.com/neutron-bomb-an-explosive-issue/ |title=Neutron bomb an explosive issue, 1981 |url-status=dead |archive-url=https://web.archive.org/web/20150228144147/http://waynebiddle.com/neutron-bomb-an-explosive-issue/ |archive-date=2015-02-28 |access-date=2014-09-04 }}</ref><ref>{{cite book|author=Muller, Richard A. |title=Physics for Future Presidents: The Science Behind the Headlines |publisher=W.W. Norton & Company |year=2009 |isbn=978-0-393-33711-2 |page=148 |url=https://books.google.com/books?id=6DBnS2g-KrQC&pg=PA148}}</ref> During the [[Cold War]], China also developed a neutron bomb but refrained from deploying it on tactical delivery systems.<ref name=":2">{{Cite book |last=Cunningham |first=Fiona S. |title=Under the Nuclear Shadow: China's Information-Age Weapons in International Security |date=2025 |publisher=[[Princeton University Press]] |isbn=978-0-691-26103-4 |location= |doi=10.2307/jj.16040335 |jstor=jj.16040335}}</ref>{{Rp|page=76}}

ERWs were first operationally deployed for [[anti-ballistic missile]]s (ABMs). In this role, the burst of neutrons would cause nearby warheads to undergo partial fission, preventing them from exploding properly. For this to work, the ABM would have to explode within approximately {{convert|100|m|ft|-2}} of its target. The first example of such a system was the [[W66 (nuclear warhead)|W66]], used on the [[Sprint (missile)|Sprint]] missile used in the US [[Nike-X]] system. It is believed the Soviet equivalent, the [[A-135 anti-ballistic missile system|A-135]]'s [[53T6]] missile, uses a similar design.<ref name="books.google.ie">{{Cite book|url=https://books.google.com/books?id=fnqN-1UaNI4C&pg=PA67|title=Soviet Ballistic Missile Defense and the Western Alliance|first=David Scott|last=Yost|date=2 February 1988|publisher=Harvard University Press|via=Google Books|isbn=9780674826106}}</ref>

The weapon was once again proposed for tactical use by the United States in the 1970s and 1980s, and production of the [[W70]] began for the [[MGM-52 Lance]] in 1981. This time, it led to protests as the growing [[anti-nuclear movement]] gained strength through this period. Opposition was so intense that European leaders refused to accept it on their territory. US President [[Ronald Reagan]] ordered the production of the W70-3, which remained in the US stockpile until they were retired in 1992. The last W70 was dismantled in February 1996.<ref>{{cite journal |last1= |first1= |last2= |first2= |title= U.S. Nuclear Weapons Stockpile, July 1996|url= |journal= Bulletin of the Atomic Scientists|year= 1996|volume= 52|issue= 4|pages= 61–63|doi=10.1080/00963402.1996.11456646 |bibcode= 1996BuAtS..52d..61.|access-date=|doi-access= free}}</ref>

==Basic concept==
In a standard thermonuclear design, a small [[fission bomb]] is placed close to a larger mass of thermonuclear fuel, usually lithium deuteride. The two components are then placed within a thick [[hohlraum|radiation case]], usually made from [[uranium]], [[lead]], or steel. The case traps the energy from the fission bomb for a brief period, allowing it to heat and compress the main thermonuclear fuel. The case is normally made of [[depleted uranium]] or [[natural uranium]] metal, because the thermonuclear reactions give off extraordinarily large numbers of high-energy [[neutron]]s that can cause fission reactions in the casing material. These can add considerable energy to the reaction; in a typical design, as much as 50% of the total energy comes from fission events in the casing. For this reason, these weapons are technically known as fission-fusion-fission designs.

In a neutron bomb, the casing material is selected either to be transparent to neutrons or to actively enhance their production. The burst of neutrons created in the thermonuclear reaction is then free to escape the bomb, outpacing the physical explosion. By carefully designing the thermonuclear stage of the weapon, the neutron burst can be maximized while minimizing the blast itself. This makes the lethal radius of the neutron burst greater than that of the explosion itself. Since the neutrons are absorbed or decay rapidly, such a burst over an enemy column would kill the crews but leave the area able to be quickly reoccupied.

Compared to a pure [[fission bomb]] with an identical explosive yield, a neutron bomb would emit about ten times<ref name=Kistiakovsky>{{cite journal |last=Kistiakovsky |first=George |title=The folly of the neutron bomb|journal=Bulletin of the Atomic Scientists |date=Sep 1978 |volume=34 |issue=7 |url=https://books.google.com/books?id=aAoAAAAAMBAJ&pg=PA27 |access-date=11 February 2011 |page=27|doi=10.1080/00963402.1978.11458533 |bibcode=1978BuAtS..34g..25K }}</ref> the amount of neutron radiation. In a fission bomb, at sea level, the total radiation pulse energy which is composed of both [[gamma ray]]s and neutrons is approximately 5% of the entire energy released; in neutron bombs, it would be closer to 40%, with the percentage increase coming from the higher production of neutrons. Furthermore, the neutrons emitted by a neutron bomb have a much higher average energy level (close to 14 M[[Electronvolt|eV]]) than those released during a fission reaction (1–2 MeV).<ref>{{cite book |author=Hafemeister, David W. |title=Physics of societal issues: calculations on national security, environment, and energy |publisher=Springer |year=2007 |isbn=978-0-387-95560-5 |page=18 |url=https://books.google.com/books?id=LT4MSqv9QUIC&pg=PA18}}</ref>

Technically speaking, every low-yield nuclear weapon is a radiation weapon, including non-enhanced variants. All nuclear weapons up to about 10 kilotons in yield have prompt neutron radiation<ref name="fas.org" /> as their furthest-reaching lethal component.  For standard weapons above about 10 kilotons of yield, the lethal blast and thermal effects radius begins to exceed the lethal [[ionizing radiation]] radius.<ref name="Mock up">{{cite web |url=http://www.remm.nlm.gov/RemmMockup_files/radiationlethality.jpg |title=Mock up |publisher=Remm.nlm.gov |access-date=2013-11-30 |url-status=live |archive-url=https://web.archive.org/web/20130607091341/http://www.remm.nlm.gov/RemmMockup_files/radiationlethality.jpg |archive-date=2013-06-07 }}</ref><ref name="johnstonsarchive1">{{cite web |url=http://www.johnstonsarchive.net/nuclear/nukgr1.gif |title=Range of weapons effects |publisher=Johnstonsarchive.net |access-date=2013-11-30 |url-status=live |archive-url=https://web.archive.org/web/20160108000905/http://www.johnstonsarchive.net/nuclear/nukgr1.gif |archive-date=2016-01-08 }}</ref><ref>{{cite web|url=http://www.webofstories.com/play/54981?o=R|title=Weapon designer Robert Christy discussing scaling laws, that is, how injuries from ionizing radiation do not linearly scale in lock step with the range of thermal flash injuries, especially as higher and higher yield nuclear weapons are used|publisher=Webofstories.com|access-date=2013-11-30|archive-date=2013-09-01|archive-url=https://archive.today/20130901131934/http://www.webofstories.com/play/robert.christy/13;jsessionid=A169C68887C651CCD55CFD5F5AB5D0D1|url-status=dead}}</ref> Enhanced radiation weapons also fall into this same yield range and simply enhance the intensity and range of the neutron dose for a given yield.

==History and deployment to present==
The conception of neutron bombs is generally credited to [[Samuel T. Cohen]] of the [[Lawrence Livermore National Laboratory]], who developed the concept in 1958.<ref>{{cite news |author=Robert D. McFadden |title=Samuel T. Cohen, Neutron Bomb Inventor, Dies at 89 |url=https://www.nytimes.com/2010/12/02/us/02cohen.html?pagewanted=all |work=[[The New York Times]] |date=December 1, 2010 |access-date=2010-12-02 |url-status=live |archive-url=https://web.archive.org/web/20120117064935/http://www.nytimes.com/2010/12/02/us/02cohen.html?pagewanted=all |archive-date=January 17, 2012 |author-link=Robert D. McFadden}}</ref> Initial development was carried out as part of projects Dove and Starling, and an early device was tested underground in early 1962. Designs for a "weaponized" version were developed in 1963.<ref name=data /><ref>"[http://chemistry.about.com/od/chemistryfaqs/f/neutronbomb.htm About: Chemistry article] {{webarchive|url=http://archive.wikiwix.com/cache/20110223160358/http://chemistry.about.com/od/chemistryfaqs/f/neutronbomb.htm |date=2011-02-23}}", by Anne Marie Helmenstine, Ph. D</ref>

Development of two production designs for the Army's [[MGM-52 Lance]] short-range missile began in July 1964, the [[W63 (nuclear warhead)|W63]] at Livermore and the [[W64 (nuclear warhead)|W64]] at [[Los Alamos National Laboratory|Los Alamos]]. Both entered phase three testing in July 1964, and the W64 was cancelled in favor of the W63 in September 1964. The W63 was in turn cancelled in November 1965 in favor of the [[W70]] (Mod 0), a conventional design.<ref name=data>{{cite book |first1=Thomas |last1=Cochran |first2=William |last2= Arkin |first3=Milton |last3=Hoenig |title= Nuclear Weapons Databook: U.S. nuclear warhead production. Volume 2 |publisher=Ballinger Publishing |year=1987 |page=23}}</ref> By this time, the same concepts were being used to develop warheads for the [[Sprint (missile)|Sprint missile]], an [[anti-ballistic missile]] (ABM), with Livermore designing the [[W65 (nuclear warhead)|W65]] and Los Alamos the [[W66 (nuclear warhead)|W66]]. Both entered phase three testing in October 1965, but the W65 was cancelled in favor of the W66 in November 1968. Testing of the W66 was carried out in the late 1960s, and it entered production in June 1974,<ref name=data /> the first neutron bomb to do so. Approximately 120 were built, with about 70 of these being on active duty during 1975 and 1976 as part of the [[Safeguard Program]]. When that program was shut down they were placed in storage, and eventually decommissioned in the early 1980s.<ref name=data />

Development of ER warheads for Lance continued, but in the early 1970s, attention had turned to using modified versions of the W70, the W70 Mod 3.<ref name=data /> Development was subsequently postponed by President [[Jimmy Carter]] in 1978 following protests against his administration's plans to deploy neutron warheads to ground forces in Europe.<ref name="On this Day: 7 April">{{cite news|title=On this Day: 7 April|url=http://news.bbc.co.uk/onthisday/hi/dates/stories/april/7/newsid_2523000/2523051.stm|publisher=[[BBC]]|date=1978-04-07|access-date=2010-07-02|url-status=live|archive-url=https://web.archive.org/web/20101207110040/http://news.bbc.co.uk/onthisday/hi/dates/stories/april/7/newsid_2523000/2523051.stm|archive-date=2010-12-07}}</ref> On [[1978 Soviet nuclear tests|November 17, 1978]], in a test, the [[Soviet Union|USSR]] detonated its first similar-type bomb.{{citation needed|date=December 2020}} President [[Ronald Reagan]] restarted production in 1981.<ref name="On this Day: 7 April" /> The Soviet Union renewed a [[propaganda]] campaign against the US's neutron bomb in 1981 following Reagan's announcement. In 1983, Reagan then announced the [[Strategic Defense Initiative]], which surpassed neutron bomb production in ambition and vision and with that, neutron bombs quickly faded from the center of the public's attention.{{citation needed|date=December 2020}}

{| class="wikitable floatright"  style="text-align:center;"
|+Attempted warhead replacement programs
|-
!Initial!!Enhanced!!Gun caliber
|-
|[[W48]]||[[W82]]||[[M109 howitzer|155 mm]]
|-
|[[W33 (nuclear weapon)|W33]]||[[W79 Artillery-Fired Atomic Projectile|W79]]||[[M110 howitzer|203mm]]
|}
Three types of enhanced radiation weapons (ERW) were deployed by the United States.<ref>{{cite news|archive-url=https://web.archive.org/web/20070929215520/http://www.omnology.com/nuclear01.html |archive-date=2007-09-29 |url=http://www.omnology.com/nuclear01.html |title=Nuclear Weapon News and Background |access-date=2012-10-11}}</ref> 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 MGM-52 Lance missile, and the [[W79 Artillery-Fired Atomic Projectile|W79 Mod 0]] was developed for [[nuclear artillery]] shells. The latter two types were retired by President [[George H. W. Bush]] in 1992, following the end of the [[Cold War]].<ref>{{cite news |author=Christopher Ruddy |title=Bomb inventor says U.S. defenses suffer because of politics |url=http://www.manuelsweb.com/sam_cohen.htm |work=[[Tribune-Review]] |date=June 15, 1997 |access-date=2010-07-03 |url-status=live |archive-url=https://web.archive.org/web/20100922125103/http://manuelsweb.com/sam_cohen.htm |archive-date=September 22, 2010 |author-link=Christopher Ruddy}}</ref><ref name="autogenerated1">{{cite web |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq1.html |title=Types of Nuclear Weapons |access-date=2012-10-12 |url-status=live |archive-url=https://web.archive.org/web/20120809054936/http://nuclearweaponarchive.org/Nwfaq/Nfaq1.html |archive-date=2012-08-09}}</ref> The last W70 Mod 3 warhead was dismantled in 1996,{{cn|date=March 2025}} and the last W79 Mod 0 was dismantled by 2003, when the dismantling of all W79 variants was completed.<ref>{{cite web |url=http://nnsa.energy.gov/sites/default/files/nnsa/news/documents/PR_NA-03-16_W-76Dismantled-LastNuclearArtilleryShell.pdf |title=NNSA Dismantles Last Nuclear Artillery Shell |publisher=National Nuclear Security Administration |access-date=2012-10-12 |url-status=dead |archive-url=https://web.archive.org/web/20111023163331/http://nnsa.energy.gov/sites/default/files/nnsa/news/documents/PR_NA-03-16_W-76Dismantled-LastNuclearArtilleryShell.pdf |archive-date=2011-10-23}}</ref>

According to the [[Cox Report]], as of 1999, the United States had never deployed a neutron weapon. The nature of this statement is not clear; it reads, "The stolen information also includes classified design information for an enhanced radiation weapon (commonly known as the "neutron bomb"), which neither the United States, nor any other nation, has ever deployed."<ref>{{cite web |title=Report Of The Select Committee On U.S. National Security And Military/Commercial Concerns With The People's Republic Of China: Chapter 2 – PRC Theft Of U.S. Thermonuclear Warhead Design Information |url=http://www.house.gov/coxreport/chapfs/ch2.html |url-status=live |archive-url=https://web.archive.org/web/20150508121324/http://www.house.gov/coxreport/chapfs/ch2.html |archive-date=2015-05-08}}</ref> However, the fact that neutron bombs had been produced by the US was well known at this time and part of the public record. Cohen suggests the report is playing with the definitions; while the US bombs were never deployed ''to Europe'', they remained stockpiled in the US.<ref>{{cite journal |first=Samuel |last=Cohen |journal=Insight on the News |date=9 August 1999 |url=https://www.questia.com/read/1G1-55426724 |title=Check Your Facts: Cox Report Bombs}}{{dead link|date=July 2021}}</ref>

In addition to the two superpowers, France and China are known to have tested neutron or enhanced radiation bombs. France conducted an early test of the technology in 1967<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/395689.stm |title=Neutron bomb: Why 'clean' is deadly |publisher=BBC News |date=1999-07-15 |access-date=2012-10-12 |url-status=live |archive-url=https://web.archive.org/web/20090407070250/http://news.bbc.co.uk/1/hi/sci/tech/395689.stm |archive-date=2009-04-07}}</ref> and tested an actual neutron bomb in 1980.<ref>UK parliamentary question on whether condemnation was considered by [[First Thatcher ministry|Thatcher government]] [https://api.parliament.uk/historic-hansard/commons/1980/jul/16/french-neutron-bomb] {{Webarchive|url=https://web.archive.org/web/20090715053705/http://hansard.millbanksystems.com/commons/1980/jul/16/french-neutron-bomb|date=2009-07-15}}</ref> China conducted a successful test of neutron bomb principles in 1984 and a successful test of a neutron bomb in 1988. However, neither of those countries chose to deploy neutron bombs. Chinese nuclear scientists stated before the 1988 test that China had no need for neutron bombs, but it was developed to serve as a "technology reserve", in case the need arose in the future.<ref>{{cite journal |last1=Ray |first1=Jonathan |title=Red China's "Capitalist Bomb": Inside the Chinese Neutron Bomb Program |journal=China Strategic Perspectives |date=January 2015 |volume=8 |url=http://inss.ndu.edu/Portals/68/Documents/stratperspective/china/ChinaPerspectives-8.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150207083547/http://inss.ndu.edu/Portals/68/Documents/stratperspective/china/ChinaPerspectives-8.pdf |archive-date=2015-02-07 |access-date=2015-02-07}}</ref>

In May 1998, Senior Pakistani Scientist, Dr. N. M. Butt, stated that "PAEC built a sufficient number of neutron bombs—a battlefield weapon that is essentially a low yield device".<ref>{{cite news|author=Raja Zulfikar |date=28 May 1998 |title=Pakistan builds a neutron bomb |work=nuclnet}}</ref>

In August 1999, the Indian government stated that India was capable of producing a neutron bomb.<ref>{{cite news|url=https://www.wsj.com/articles/SB934836102919955535|title=India Discloses It Is Able To Build a Neutron Bomb|last=Journal|first=Jonathan Karp Staff Reporter of The Wall Street|newspaper=Wall Street Journal|date=17 August 1999|url-status=live|archive-url=https://web.archive.org/web/20170123001427/http://www.wsj.com/articles/SB934836102919955535|archive-date=2017-01-23}}</ref>

Although no country is currently known to deploy them in an offensive manner, all thermonuclear [[dial-a-yield]] warheads that have about 10 kiloton and lower as one dial option, with a considerable fraction of that yield derived from fusion reactions, can be considered able to be neutron bombs in use, if not in name. The only country definitely known to deploy dedicated (that is, not dial-a-yield) neutron warheads for any length of time is the Soviet Union/[[Russia]],<ref name="books.google.ie" /> which inherited the USSR's neutron warhead equipped [[ABM-3 Gazelle]] missile program. This ABM system contains at least 68 neutron warheads with a 10-kiloton yield each and it has been in service since 1995, with inert missile testing approximately every other year since then (2014). The system is designed to destroy incoming endoatmospheric nuclear warheads aimed at [[Moscow]] and other targets and is the lower-tier/last umbrella of the [[A-135 anti-ballistic missile system]] (NATO reporting name: ABM-3).{{cn|date=March 2025}}

By 1984, according to [[Mordechai Vanunu]], Israel was mass-producing neutron bombs.<ref>''The Nuclear Express: A Political History of the Bomb and Its Proliferation'', By Thomas C. Reed, Danny B. Stillman (2010), page 181</ref>

Considerable controversy arose in the US and Western Europe following a June 1977 ''[[Washington Post]]'' exposé describing US government plans to equip US Armed Forces with neutron bombs. The article focused on the fact that it was the first weapon specifically intended to kill humans with radiation.<ref>{{cite book |author=Wittner, Lawrence S.|title=Confronting the bomb: a short history of the world nuclear disarmament movement |publisher=Stanford University Press |year=2009|isbn=978-0-8047-5632-7|pages=[https://archive.org/details/confrontingbombs0000witt/page/132 132]–133 |url=https://archive.org/details/confrontingbombs0000witt|url-access=registration}}</ref><ref>{{cite book|author=Auten, Brian J. |title=Carter's conversion: the hardening of American defense policy |publisher=University of Missouri Press |year=2008 |isbn=978-0-8262-1816-2 |page=[https://archive.org/details/cartersconversio00aute/page/134 134] |url=https://archive.org/details/cartersconversio00aute|url-access=registration}}</ref> Lawrence Livermore National Laboratory director [[Harold Brown (Secretary of Defense)|Harold Brown]] and Soviet General Secretary [[Leonid Brezhnev]] both described neutron bombs as a "capitalist bomb", because it was designed to destroy people while preserving property.<ref>{{cite book |url=https://books.google.com/books?id=7TshAQAAIAAJ&pg=PA115 |title=National security for a new era: globalization and geopolitics after Iraq |first=Donald |last=Snow |year=2008 |page=115 |publisher=Pearson Longman |isbn=978-0-205-62225-2}}</ref><ref>{{Cite book|author=Herken, Greff|title=Brotherhood of the Bomb: The Tangled Lives and Loyalties of Robert Oppenheimer, Ernest Lawrence, and Edward Teller |publisher=Macmillan|year=2003|isbn=978-0-8050-6589-3 |page=332|url=https://books.google.com/books?id=7s0NGIfflOgC&pg=PA332}}</ref>{{request quotation|date=August 2015}}

==Use==
[[File:Probable Axes of Attack.svg|thumb|right|The 1979 Soviet/Warsaw Pact invasion plan, "[[Seven Days to the River Rhine]]" to seize [[West Germany]] in the event of a nuclear attack on Poland by NATO forces. Soviet analysts had correctly assumed that the NATO response would be to use regular [[tactical nuclear weapon]]s to stop such a massive Warsaw Pact invasion.<ref>{{cite web|url=http://www.isn.ethz.ch/Digital-Library/Articles/Detail/?lng=en&id=107840|title=Poland reveals Warsaw Pact war plans|author=ISN Editors|website=International Relations And Security Network|access-date=23 December 2014|archive-url=https://archive.today/20131008004043/http://www.isn.ethz.ch/Digital-Library/Articles/Detail/?lng=en&id=107840|archive-date=8 October 2013|url-status=dead}}</ref> According to proponents, neutron bombs would blunt an invasion by Soviet tanks and armored vehicles without causing as much damage or civilian deaths as the older nuclear weapons would.<ref name="waynebiddle.com"/> Neutron bombs would have been used if the [[REFORGER]] conventional response of [[NATO]] to the invasion was too slow or ineffective.<ref name="waynebiddle.com"/><ref name="LA Times 1987">{{Cite journal |title=Senate Permits Study for New Tactical Nuclear Missile |journal=[[Los Angeles Times]] |first=Melissa |last=Healy |date=October 3, 1987 |url=https://www.latimes.com/archives/la-xpm-1987-10-03-mn-2950-story.html |access-date=2012-08-08 |url-status=live |archive-url=https://web.archive.org/web/20121223231411/http://articles.latimes.com/1987-10-03/news/mn-2950_1_intermediate-range-nuclear-forces |archive-date=December 23, 2012 }}</ref>]]

Neutron bombs are purposely designed with explosive yields lower than other nuclear weapons. Since neutrons are scattered and absorbed by air,<ref name="fas.org" /> neutron radiation effects drop off rapidly with distance in air. As such, there is a sharper distinction, relative to thermal effects, between areas of high lethality and areas with minimal radiation doses.<ref name="The Neutron Bomb"/> No high yield (more than c.&nbsp;10&nbsp;[[kiloton]]) nuclear bombs, including the extreme example of the 50 [[TNT equivalent|megaton]] [[Tsar Bomba]], are able to radiate sufficient neutrons beyond their lethal blast range when detonated as a surface burst or low altitude [[air burst]] and so are not classified as neutron bombs, thus limiting the yield of neutron bombs to a maximum of about 10 kilotons. The intense [[Pulse (physics)|pulse]] of high-energy neutrons generated by a neutron bomb is the principal killing mechanism, not the fallout, heat or blast.

The inventor of the neutron bomb, Sam Cohen, criticized the description of the W70 as a neutron bomb since it could be configured to yield 100 kilotons:

{{blockquote|the W-70 ... is not even remotely a "neutron bomb." Instead of being the type of weapon that, in the popular mind, "kills people and spares buildings" it is one that both kills and physically destroys on a massive scale. The W-70 is not a discriminate weapon, like the neutron bomb—which, incidentally, should be considered a weapon that "kills enemy personnel while sparing the physical fabric of the attacked populace, and even the populace too."<ref>{{cite magazine
 |title       = Check Your Facts: Cox Report Bombs
 |url         = https://www.questia.com/read/1G1-55426724/check-your-facts-cox-report-bombs
 |magazine   = Insight on the News
 |access-date  = 5 June 2015
 |date        = 9 August 1999
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20160304064930/https://www.questia.com/read/1G1-55426724/check-your-facts-cox-report-bombs
 |archive-date = 4 March 2016
}}</ref>}}

Although neutron bombs are commonly believed to "leave the infrastructure intact", with current designs that have explosive yields in the low kiloton range,<ref>{{cite web |url=http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html |title=List of All U.S. Nuclear Weapons |date=2006-10-14 |access-date=2012-10-12 |url-status=live |archive-url=https://web.archive.org/web/20130208030000/http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html |archive-date=2013-02-08 }}</ref> detonation in (or above) a built-up area would still cause a sizable degree of building destruction, through blast and heat effects out to a moderate radius, albeit considerably less destruction, than when compared to a standard nuclear bomb of the ''exact'' same total energy release or "yield".<ref name="chemistry.about.com">{{cite web |url=http://chemistry.about.com/od/chemistryfaqs/f/neutronbomb.htm |title=What Is a Neutron Bomb? By Anne Marie Helmenstine, Ph.D |url-status=dead |archive-url=https://web.archive.org/web/20110105165334/http://chemistry.about.com/od/chemistryfaqs/f/neutronbomb.htm |archive-date=2011-01-05 |access-date=2007-04-20 }}</ref>

[[Image:M110 Column.JPEG|thumb|right|U.S. Army [[M110 howitzer]]s in a 1984 REFORGER staging area before transport. This dual capable system could fire nuclear artillery shells.<ref>{{cite web|url=http://www.orbat85.nl/order-of-battle/royal-army/1-nl-corps/1-lka.html#dual-capable-artillery|title=1 (NL) Corps Artillery • 1 Legerkorpsartillerie (1 Lka)|first=Hans|last=Boersma|website=www.orbat85.nl|url-status=dead|archive-url=https://web.archive.org/web/20150924061340/http://www.orbat85.nl/order-of-battle/royal-army/1-nl-corps/1-lka.html#dual-capable-artillery|archive-date=2015-09-24|access-date=2015-08-30}}</ref><ref>{{cite web|url=http://www.llnl.gov/50th_anniv/decades/1970s.htm|title=Accomplishments in the 1970s: LLNL's 50th Anniversary|date=17 February 2005|url-status=dead|archive-url=https://web.archive.org/web/20050217061020/http://www.llnl.gov/50th_anniv/decades/1970s.htm|archive-date=17 February 2005}}</ref>]]

The [[Cold War tank formations|Warsaw Pact tank strength was over twice that of NATO]], and [[Soviet deep battle#Central Europe|Soviet deep battle doctrine]] was likely to be to use this numerical advantage to rapidly sweep across continental Europe if the Cold War ever turned hot. Any weapon that could break up their intended mass tank formation deployments and force them to deploy their tanks in a thinner, more [[Defeat in detail|easily dividable manner]],<ref name="waynebiddle.com"/> would aid ground forces in the task of hunting down solitary tanks and using [[List of anti-tank missiles|anti-tank missiles]] against them,<ref>{{cite web |url=http://www.manuelsweb.com/neutronbomb.htm |title=what is a neutron bomb "In strategic terms, the neutron bomb has a theoretical deterrent effect: discouraging an armoured ground assault by arousing the fear of neutron bomb counterattack" |url-status=dead |archive-url=https://web.archive.org/web/20060113000504/http://www.manuelsweb.com/neutronbomb.htm |archive-date=2006-01-13 |access-date=2005-12-21 }}</ref> such as the contemporary [[M47 Dragon]] and [[BGM-71 TOW]] missiles, of which NATO had hundreds of thousands.<ref name="waynebiddle.com"/>

Rather than making extensive preparations for battlefield nuclear combat in Central Europe, the Soviet military leadership believed that conventional superiority provided the Warsaw Pact with the means to approximate the effects of nuclear weapons and achieve victory in Europe without resort to those weapons.<ref>{{cite web|url=http://www.gwu.edu/~nsarchiv//nukevault/ebb285/|title=Candid Interviews with Former Soviet Officials Reveal U.S. Strategic Intelligence Failure Over Decades|website=www.gwu.edu|url-status=live|archive-url=https://web.archive.org/web/20110805060352/http://www.gwu.edu/~nsarchiv/nukevault/ebb285/|archive-date=2011-08-05}}</ref>

Neutron bombs, or more precisely, enhanced [neutron] radiation weapons were also to find use as strategic anti-ballistic missile weapons,<ref name="chemistry.about.com"/> and in this role, they are believed to remain in active service within Russia's Gazelle missile.<ref name="books.google.ie"/>

===Effects===
[[File:House 1953 Nevada Nuclear Test 5 psi.jpg|thumb|A wooden framed house photographed during a 1953 nuclear test, {{convert|5|psi|kPa}} overpressure, full collapse.]]

Upon detonation, a near-ground [[air burst|airburst]] of a 1-kiloton neutron bomb would produce a large blast wave and a powerful pulse of both thermal radiation and [[ionizing radiation]] in the form of fast (14.1{{spaces}}[[Electronvolt|MeV]]) neutrons. The thermal pulse would cause [[third degree burn]]s to unprotected skin out to approximately 500 meters. The blast would create pressures of at least 4.6{{spaces}}psi (32 kPa) out to a radius of 600 meters, which would severely damage all non-reinforced concrete structures. At the conventional effective combat range against modern [[main battle tank]]s and [[armored personnel carrier]]s (<{{spaces}}690–900{{spaces}}m), the blast from a 1{{spaces}}kt neutron bomb would destroy or damage to the point of nonusability almost all un-reinforced civilian buildings.{{Citation needed|date=October 2021|reason=A blast wave of 4.6psi is 0.3 atmospheres, significantly less than ambient atmospheric pressure; this would not cause damage to buildings. Perhaps an increase of 4.6 psi was intended, but still unsubstantiated.}}

Using neutron bombs to stop an enemy armored attack by rapidly incapacitating crews with a dose of 80+ [[Gray (unit)|Gy]] of radiation<ref name="Fact-index, neutron bomb">{{cite web |url=http://www.fact-index.com/n/ne/neutron_bomb_1.html |title=Fact-index, neutron bomb |url-status=dead |archive-url=https://web.archive.org/web/20130630093824/http://www.fact-index.com/n/ne/neutron_bomb_1.html |archive-date=2013-06-30 |access-date=2014-08-09 }}</ref> would require exploding large numbers of them to blanket the enemy forces, destroying all normal civilian buildings within c.{{spaces}}600 meters of the immediate area.<ref name="Fact-index, neutron bomb" /><ref>Calculated from {{cite web |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html |title=Effects of Nuclear Explosions |access-date=2014-04-21 |url-status=live |archive-url=https://web.archive.org/web/20140428174041/http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html |archive-date=2014-04-28 }} assuming 0.5{{spaces}}kt combined blast and thermal</ref> [[Neutron activation]] from the explosions could make many building materials in the city radioactive, such as [[galvanized steel]] (see [[#Use as an area denial weapon|area denial use]] below).

Because liquid-filled objects like the human body are resistant to gross overpressure, the 4–5{{spaces}}psi (28-34 kPa) blast [[overpressure]] would cause very few direct casualties at a range of c.{{spaces}}600{{spaces}}m. The powerful winds produced by this overpressure, however, could throw bodies into objects or throw debris at high velocity, including window glass, both with potentially lethal results. Casualties would be highly variable depending on surroundings, including potential building collapses.<ref>{{cite web |url=https://www.cdc.gov/niosh/docket/archive/pdfs/NIOSH-125/125-ExplosionsandRefugeChambers.pdf |title=1) Effects of blast pressure on the human body |access-date=2012-10-12 |url-status=live |archive-url=https://web.archive.org/web/20130127040629/http://www.cdc.gov/niosh/docket/archive/pdfs/NIOSH-125/125-ExplosionsandRefugeChambers.pdf |archive-date=2013-01-27 }}</ref>

The pulse of neutron radiation would cause immediate and permanent incapacitation to unprotected outdoor humans in the open out to 900 meters,<ref name="Kistiakovsky" /> with death occurring in one or two days. The [[median lethal dose]] (LD<sub>50</sub>) of 6 Gray would extend to between 1350 and 1400 meters for those unprotected and outdoors,<ref name="Fact-index, neutron bomb" /> where approximately half of those exposed would die of radiation sickness after several weeks.

A human residing within, or simply shielded by, at least one concrete building with walls and ceilings {{convert|30|cm|in|abbr=on}} thick, or alternatively of damp [[soil]] 24 inches (60&nbsp;cm) thick, would receive a neutron radiation exposure reduced by a factor of 10.<ref name="web.mit.edu">{{cite web |url=http://web.mit.edu/ans/www/documents/seminar/F07/rydin.ppt |title=Applications of the Monte Carlo Adjoint Shielding Methodology - MIT |url-status=live |archive-url=https://web.archive.org/web/20150717132012/http://web.mit.edu/ans/www/documents/seminar/F07/rydin.ppt |archive-date=2015-07-17 }}</ref> Even near ground zero, basement sheltering or buildings with similar radiation shielding characteristics would drastically reduce the radiation dose.<ref name="waynebiddle.com"/>

Furthermore, the [[neutron absorption]] spectrum of air is disputed by some authorities, and depends in part on absorption by [[hydrogen]] from [[water vapor]]. Thus, absorption might vary exponentially with humidity, making neutron bombs far more deadly in [[desert climate]]s than in humid ones.<ref name="Fact-index, neutron bomb" />

===Effectiveness in modern anti-tank role===
{{see also|Centurion Tank#Nuclear tests|Object 279|Signs and symptoms of radiation poisoning#"Walking Ghost phase"}}
[[File:Neutroncrosssectionboron.png|thumb|The [[neutron cross section]] and absorption probability in [[Barn (unit)|barns]] of the two natural [[boron]] isotopes (top curve is for 10&nbsp;B and bottom curve for 11&nbsp;B. As neutron energy increases to 14&nbsp;MeV, the absorption effectiveness, in general, decreases. Thus, for boron-containing armor to be effective, fast neutrons must first be slowed by another element by [[neutron scattering]].]]

The questionable effectiveness of ER weapons against modern tanks is cited as one of the main reasons that these weapons are no longer fielded or [[Nuclear stockpile|stockpiled]]. With the increase in average tank armor thickness since the first ER weapons were fielded, it was argued in the March 13, 1986, ''New Scientist'' magazine that tank armor protection was approaching the level where tank crews would be almost fully protected from radiation effects. Thus, for an ER weapon to incapacitate a modern tank crew through irradiation, the weapon must be detonated at such proximity to the tank that the [[nuclear explosion]]'s blast would now be equally effective at incapacitating it and its crew.<ref>{{cite book |url=https://books.google.com/books?id=mYVNkaEJpz4C&q=%22main+battle+tank%22&pg=PA47 |title=New Scientist March 13, 1986 pg 45 |date=1986-03-13 |access-date=2012-10-12 |last1=Information |first1=Reed Business }}{{Dead link|date=November 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

However, although the author did note that effective [[Neutron radiation#Health hazards and protection|neutron absorbers]] and [[neutron poison]]s such as [[boron carbide]] can be incorporated into conventional armor and strap-on [[neutron moderator|neutron moderating]] hydrogenous material (substances containing hydrogen atoms), such as explosive [[reactive armor]], increasing the protection factor, the author holds that in practice, combined with [[neutron scattering]], the actual average total tank area protection factor is rarely higher than 15.5 to 35.<ref>{{cite book|url=https://books.google.com/books?id=RYH7o-4ykmMC&pg=PA62|title=New Scientist June 12, 1986 pg 62|last1=Information|first1=Reed Business|date=1986-06-12}}{{Dead link|date=November 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> According to the [[Federation of American Scientists]], the neutron protection factor of a "tank" can be as low as 2,<ref name="fas.org" /> without qualifying whether the statement implies a [[light tank]], [[medium tank]], or [[main battle tank]].

A composite [[Types of concrete#High-performance concrete|high-density concrete]], or alternatively, a laminated [[Radiation protection#Radiation protection|graded-Z shield]], 24 units thick of which 16 units are iron and 8 units are [[polyethylene]] containing boron (BPE), and additional mass behind it to attenuate neutron capture gamma rays, is more effective than just 24 units of pure iron or BPE alone, due to the advantages of both iron and BPE in combination. During [[neutron transport]], iron is effective in slowing down/scattering high-energy neutrons in the 14-MeV energy range and attenuating gamma rays, while the hydrogen in polyethylene is effective in slowing down these now slower [[fast neutrons]] in the few MeV range, and boron-10 has a high absorption cross section for [[thermal neutrons]] and a low production yield of gamma rays when it absorbs a neutron.<ref>{{cite web |url=https://www.slac.stanford.edu/pubs/slacpubs/7750/slac-pub-7785.pdf |title=Monte Carlo Calculations Using MCNP4B for an Optimal Shielding Design of a 14-MeV Neutron Source, Submitted to the Journal of Radiation Protection Dosimetry 1998 |url-status=live |archive-url=https://web.archive.org/web/20160305193733/https://www.slac.stanford.edu/pubs/slacpubs/7750/slac-pub-7785.pdf |archive-date=2016-03-05 }}</ref><ref>{{cite web |url=http://www.uthgsbsmedphys.org/gs02-0093/3.3b-neutroninteractions.pdf |title=Neutron Interactions – Part 2 George Starkschall, Ph.D. Department of Radiation Physics |url-status=dead |archive-url=https://web.archive.org/web/20150717162239/http://www.uthgsbsmedphys.org/gs02-0093/3.3b-neutroninteractions.pdf |archive-date=2015-07-17 |access-date=2014-03-02 }}</ref><ref>{{cite web |url=http://ocw.mit.edu/courses/nuclear-engineering/22-55j-principles-of-radiation-interactions-fall-2004/lecture-notes/ener_depo_neutro.pdf |title=22.55 "Principles of Radiation Interactions" |url-status=live |archive-url=https://web.archive.org/web/20150717104916/http://ocw.mit.edu/courses/nuclear-engineering/22-55j-principles-of-radiation-interactions-fall-2004/lecture-notes/ener_depo_neutro.pdf |archive-date=2015-07-17 }}</ref> The Soviet [[T-72]] tank, in response to the neutron bomb threat, is cited as having fitted a boronated<ref>{{cite web |url=http://www.manuelsweb.com/neutronbomb.htm |title=What is a neutron bomb |url-status=dead |archive-url=https://web.archive.org/web/20060113000504/http://www.manuelsweb.com/neutronbomb.htm |archive-date=2006-01-13 |access-date=2005-12-21 }}</ref> polyethylene liner, which has had its neutron shielding properties simulated.<ref name="web.mit.edu"/><ref>{{cite book |url=https://books.google.com/books?id=bGWYl-ugjPgC&q=t72+tank+boron+neutron&pg=PA418 |title=Terror Reigns Again By Ronan Strobing. pg 418|isbn=9780955855771|last1=Strobing|first1=Ronan|date=Jul 2009|publisher=ShieldCrest }}</ref>

[[File:Neutron radiation weighting factor as a function of kinetic energy.gif|thumb|upright=1.35|The [[Relative biological effectiveness|radiation weighting factor]] for neutrons of various energy has been revised over time and certain agencies have different weighting factors; despite the variation amongst the agencies, from the graph, for a given energy, a [[fusion neutron]] (14.1&nbsp;MeV) although more energetic, is less biologically harmful as rated in [[sievert]]s, than a fission-generated thermal neutron or a fusion neutron slowed to that energy, c.&nbsp;0.8&nbsp;MeV.]]
However, some tank armor material contains [[depleted uranium]] (DU), common in the US's [[M1A1 Abrams]] tank, which incorporates steel-encased depleted uranium armor,<ref>{{cite web |url=http://www.army-technology.com/projects/abrams |title=M1A1/2 Abrams Main Battle Tank, United States of America |url-status=live |archive-url=https://web.archive.org/web/20140810045337/http://www.army-technology.com/projects/abrams |archive-date=2014-08-10 }}</ref> a substance that will fast fission when it [[neutron capture|captures]] a fast, fusion-generated neutron, and thus on fissioning will produce [[thermal neutrons|fission neutrons]] and [[fission product]]s embedded within the armor, products which emit, among other things, penetrating gamma rays. Although the neutrons emitted by the neutron bomb may not penetrate to the tank crew in lethal quantities, the fast fission of DU within the armor could still ensure a lethal environment for the crew and maintenance personnel by fission neutron and gamma ray exposure{{dubious|date=April 2017}},<ref>{{cite web|url=http://chemistry.about.com/od/chemistryfaqs/f/neutronbomb.htm|title=For example, M-1 tank armor includes depleted uranium, which can undergo fast fission and can be made to be radioactive when bombarded with neutrons|url-status=dead|archive-url=https://web.archive.org/web/20110105165334/http://chemistry.about.com/od/chemistryfaqs/f/neutronbomb.htm|archive-date=2011-01-05|access-date=2007-04-20}}</ref>{{Unreliable source?|date=April 2017}} largely depending on the exact thickness and elemental composition of the armor—information usually hard to attain. Despite this, [[Ducrete]]—which has an elemental composition similar (but not identical) to the ceramic [[Chobham Armour#Heavy metal modules|second-generation heavy metal Chobham armor]] of the Abrams tank—is an effective radiation shield, to both fission neutrons and gamma rays due to it being a graded-Z material.<ref>{{cite web |url=http://web.ead.anl.gov/uranium/pdf/ducretecosteffec.pdf |title=Archived copy |access-date=2011-11-29 |url-status=dead |archive-url=https://web.archive.org/web/20111019052835/http://web.ead.anl.gov/uranium/pdf/ducretecosteffec.pdf |archive-date=2011-10-19 }} Paper Summary Submitted to Spectrum 2000, Sept 24-28, 2000, Chattanooga, TN. Ducrete: A Cost Effective Radiation Shielding Material. Quote- "The Ducrete/DUAGG replaces the conventional aggregate in concrete producing concrete with a density of 5.6 to 6.4&nbsp;g/cm3 (compared to 2.3&nbsp;g/cm3 for conventional concrete). This shielding material has the unique feature of having both high Z and low Z elements in a single matrix. Consequently, it is very effective for the attenuation of gamma and neutron radiation&nbsp;..."</ref><ref>M. J. Haire and S. Y. Lobach, [http://www.ornl.gov/~webworks/cppr/y2001/pres/124687.pdf "Cask size and weight reduction through the use of depleted uranium dioxide (DUO<sub>2</sub>)-concrete material"] {{webarchive|url=https://web.archive.org/web/20120926214404/http://www.ornl.gov/~webworks/cppr/y2001/pres/124687.pdf |date=2012-09-26 }}, Waste Management 2006 Conference, Tucson, Arizona, February 26–March 2, 2006.</ref> Uranium, being about twice as dense as lead, is thus nearly twice as effective at shielding gamma ray radiation per unit thickness.<ref>{{cite web |url=https://www.nde-ed.org/EducationResources/CommunityCollege/RadiationSafety/safe_use/shielding.htm |title=Half-Value Layer (Shielding) |url-status=dead |archive-url=https://web.archive.org/web/20140811021451/https://www.nde-ed.org/EducationResources/CommunityCollege/RadiationSafety/safe_use/shielding.htm |archive-date=2014-08-11 |access-date=2014-08-09 }}</ref>

===Use against ballistic missiles===
As an anti-ballistic missile weapon, the first fielded ER warhead, the W66, was developed for the Sprint missile system as part of the Safeguard Program to protect United States cities and [[missile silo]]s from incoming Soviet warheads.

A problem faced by Sprint and similar ABMs was that the blast effects of their warheads change greatly as they climb and the atmosphere thins out. At higher altitudes, starting around {{convert|60,000|feet}} and above, the blast effects begin to drop off rapidly as the air density becomes very low. This can be countered by using a larger warhead, but then it becomes too powerful when used at lower altitudes. An ideal system would use a mechanism that was less sensitive to changes in air density.

Neutron-based attacks offer one solution to this problem. The burst of neutrons released by an ER weapon can induce fission in the fissile materials of primary in the target warhead. The energy released by these reactions may be enough to melt the warhead, but even at lower fission rates, the "burning up" of some of the fuel in the primary can cause it to fail to explode properly, or "fizzle".<ref name=w47>{{cite book |url=https://books.google.com/books?id=6m43DAAAQBAJ&pg=PA323 |title=British Nuclear Weapons and the Test Ban 1954–1973 |first=John |last=Walker |publisher=Routledge |date=2016 |pages=23, 323–325|isbn=978-1-317-17170-6}}</ref> Thus, a small ER warhead can be effective across a wide altitude band, using blast effects at lower altitudes and the increasingly long-ranged neutrons as the engagement rises.

The use of neutron-based attacks was discussed as early as the 1950s, with the US [[United States Atomic Energy Commission|Atomic Energy Commission]] mentioning weapons with a "clean, enhanced neutron output" for use as "antimissile defensive warheads."<ref name=bomarc>{{cite magazine |url=http://www.rcaf-arc.forces.gc.ca/en/cf-aerospace-warfare-centre/elibrary/journal/2014-vol3-iss4-08-secrets-of-the-bomarc-part-2.page#note47 |title=Secrets of the BOMARC: Re-examining Canada's Misunderstood Missile |date=Fall 2014 |first=Sean |last=Maloney |access-date=2018-10-05 |archive-date=2018-08-10 |archive-url=https://web.archive.org/web/20180810021236/http://www.rcaf-arc.forces.gc.ca/en/cf-aerospace-warfare-centre/elibrary/journal/2014-vol3-iss4-08-secrets-of-the-bomarc-part-2.page#note47 |url-status=dead }}</ref> Studying, improving and defending against such attacks was a major area of research during the 1950s and '60s. A particular example of this is the US [[UGM-27 Polaris|Polaris A-3]] missile, which delivered three warheads travelling on roughly the same trajectory, and thus with a short distance between them. A single ABM could conceivably destroy all three through neutron flux. Developing warheads that were less sensitive to these attacks was also a major area of research in the US and UK during the 1960s.<ref name=w47 />

Some sources claim that the neutron flux attack was also the main design goal of the various nuclear-tipped anti-aircraft weapons like the [[AIM-26 Falcon]] and [[CIM-10 Bomarc]]. One [[F-102]] pilot noted:

{{blockquote|GAR-11/AIM-26 was primarily a weapon-killer. The bomber(s, if any) was collateral damage. The weapon was proximity-fused to ensure detonation close enough so an intense flood of neutrons would result in an instantaneous nuclear reaction (NOT full-scale) in the enemy weapon's pit; rendering it incapable of functioning as designed ... [O]ur first "neutron bombs" were the GAR-11 and MB-1 Genie.<ref name=bomarc />}}

It has also been suggested that neutron flux's effects on the warhead electronics are another attack vector for ER warheads in the ABM role. [[Ionization]] greater than 50 [[Gray (unit)|Gray]] in [[silicon chips]] delivered over seconds to minutes will degrade the function of [[semiconductors]] for long periods.<ref>{{cite web |url=https://www.fas.org/nuke/intro/nuke/radiation.htm |title=FAS Nuclear Weapon Radiation Effects |url-status=live |archive-url=https://web.archive.org/web/20130721195639/http://www.fas.org/nuke/intro/nuke/radiation.htm |archive-date=2013-07-21}}</ref> However, while such attacks might be useful against guidance systems, which used relatively advanced electronics, in the ABM role, these components have long ago separated from the warheads by the time they come within range of the interceptors. The electronics in the warheads themselves tend to be very simple, and hardening them was one of the many issues studied in the 1960s.<ref name=w47 />

[[Lithium hydride|Lithium-6 hydride]] (Li6H) is cited as being used as a countermeasure to reduce the vulnerability and "harden" nuclear warheads from the effects of externally generated neutrons.<ref>{{cite web |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq12.html |title=Section 12.0 Useful Tables Nuclear Weapons Frequently Asked Questions |quote=Due to moderating ability and light weight, used to harden weapons against outside neutron fluxes (especially in combination with Li-6) ...The very high cross section of this reaction for thermalized neutrons, combined with the light weight of the Li-6 atom, make it useful in the form of lithium hydride for hardening of nuclear weapons against external neutron fluxes. |url-status=live |archive-url=http://archive.wikiwix.com/cache/20110224033350/http://nuclearweaponarchive.org/Nwfaq/Nfaq12.html |archive-date=2011-02-24}}</ref><ref>{{cite web |url=https://www.osti.gov/opennet/forms.jsp?formurl=document/rdd-1/drwcrtf4.html |title=''Restricted Data Declassification Policy, 1946 to the Present RDD-1'' |quote=The fact that Li6H is used in unspecified weapons for hardening |url-status=live |archive-url=https://web.archive.org/web/20131020234426/https://www.osti.gov/opennet/forms.jsp?formurl=document%2Frdd-1%2Fdrwcrtf4.html |archive-date=2013-10-20}}</ref> [[Radiation hardening]] of the warhead's electronic components as a countermeasure to high altitude neutron warheads somewhat reduces the range that a neutron warhead could successfully cause an unrecoverable [[glitch]] by the ''transient radiation effects on electronics'' (TREE) effects.<ref>{{cite web |url=http://www.acq.osd.mil/ncbdp/nm/nm_book_5_11/appendix_F.htm |title=The Nuclear Matters Handbook, F.13 |url-status=dead |archive-url=https://web.archive.org/web/20130302091606/http://www.acq.osd.mil/ncbdp/nm/nm_book_5_11/appendix_F.htm |archive-date=2013-03-02}}</ref><ref>{{cite web |url=http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA302734 |title=Transient Radiation Effects on Electronics (TREE) Handbook Formerly Design Handbook for TREE, Chapters 1-6 |url-status=dead |archive-url=https://web.archive.org/web/20140506094200/http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA302734 |archive-date=2014-05-06 |access-date=2014-05-06}}</ref>

At very high altitudes, at the edge of the atmosphere and above it, another effect comes into play. At lower altitudes, the [[X-ray]]s generated by the bomb are absorbed by the air and have [[mean free path]]s on the order of meters. But as the air thins out, the X-rays can travel further, eventually outpacing the area of effect of the neutrons. In [[exoatmospheric]] explosions, this can be on the order of {{convert|10|km}} in radius. In this sort of attack, it is the X-rays promptly delivering energy on the warhead surface that is the active mechanism; the rapid ablation (or "blowoff") of the surface creates shock waves that can break up the warhead.<ref>{{cite web |url=http://www.acq.osd.mil/ncbdp/nm/nm_book_5_11/appendix_G.htm |title=Nuclear Matters Handbook |quote=Nuclear weapon-generated X-rays are the chief threat to the survival of strategic missiles in-flight above the atmosphere and to satellites ... The Neutron and gamma ray effects dominate at lower altitudes where the air absorbs most of the X-rays. |url-status=dead |archive-url=https://web.archive.org/web/20140506095559/http://www.acq.osd.mil/ncbdp/nm/nm_book_5_11/appendix_G.htm |archive-date=2014-05-06}}</ref>

===Use as an area denial weapon===
In November 2012, British Labour peer [[Lord Gilbert]] suggested that multiple enhanced radiation reduced blast (ERRB) warheads could be detonated in the mountain region of the Afghanistan-Pakistan border to prevent infiltration.<ref>{{cite web|url=http://www.huffingtonpost.co.uk/2012/11/26/lord-gilbert-neutron-bomb_n_2190607.html|title=Huffington Post|date=26 November 2012|access-date=2012-11-27|url-status=live|archive-url=https://web.archive.org/web/20121129031522/http://www.huffingtonpost.co.uk/2012/11/26/lord-gilbert-neutron-bomb_n_2190607.html|archive-date=2012-11-29}}</ref> He proposed to warn the inhabitants to evacuate, then irradiate the area, making it unusable and impassable.<ref>{{cite web |url=https://www.theguardian.com/politics/2013/jun/03/lord-gilbert |title=Lord Gilbert obituary, by Andrew Roth, 3 June 2013. "Nobody lives up in the mountains on the border between Afghanistan and Pakistan except for a few goats and a handful of people herding them," he observed. "If you told them that some ... warheads were going to be dropped there and that it would be a very unpleasant place to go, they would not go there." |website=[[TheGuardian.com]] |date=3 June 2013 |url-status=live |archive-url=https://web.archive.org/web/20140306215444/http://www.theguardian.com/politics/2013/jun/03/lord-gilbert |archive-date=6 March 2014 }}</ref>  Used in this manner, the neutron bomb(s), regardless of burst height, would release [[neutron activation|neutron activated]] casing materials used in the bomb, and depending on burst height, create radioactive soil [[neutron activation|activation products]].

In much the same fashion as the [[area denial]] effect resulting from fission product (the substances that make up most [[fallout]]) contamination in an area following a conventional [[surface burst|surface-burst]] nuclear explosion, as considered in the Korean War by [[Douglas MacArthur]], it would thus be a form of [[radiological warfare]]—with the difference that neutron bombs produce half, or less, of the quantity of fission products relative to the same-yield pure [[fission bomb]]. Radiological warfare with neutron bombs that rely on [[Teller-Ulam design|fission primaries]] would thus still produce fission fallout, albeit a comparatively ''cleaner'' and shorter-lasting version of it in the area than if air bursts were used, as little to no fission products would be deposited on the direct immediate area, instead becoming diluted global [[fallout]].
[[Image:Deuterium-tritium fusion.svg|thumb|The easiest to achieve fusion reaction, of [[deuterium]] ("D) with [[tritium]] (T") creating [[helium-4]], freeing a [[neutron]], and releasing only 3.5 [[Electronvolt|MeV]] in the form of kinetic energy as the charged [[alpha particle]] that will [[bremstrahlung|inherently generate heat]] (which manifests as blast and thermal effects), while the majority of the energy of the reaction (14.1 MeV) is carried away by the uncharged [[fast neutron]].<ref name=Shultis>
{{cite book
 |author1=Shultis, J.K.  |author2=Faw, R.E.
  |name-list-style=amp |year=2002
 |title=Fundamentals of nuclear science and engineering
 |url=https://books.google.com/books?id=SO4Lmw8XoEMC&pg=PA151
 |page=151
 |publisher=[[CRC Press]]
 |isbn=978-0-8247-0834-4
}}</ref> Devices with a higher proportion of yield derived from this reaction would be more efficient in the stand-off [[asteroid impact avoidance]] role, due to the [[mean free path|penetrative depth of fast-neutrons]] and the resulting higher [[momentum transfer]] that is produced in this "scabbing" of a much larger mass of material free from the main body, as opposed to the shallower surface penetration and [[ablation]] of [[regolith]], that is produced by thermal/soft X-rays.]]
A militarily useful use of a neutron bomb with respect to area denial would be to encase it in a thick shell of material that could be neutron activated, and use a surface burst. In this manner, the neutron bomb would be turned into a ''[[salted bomb]]''; for example, [[Isotopes of zinc|zinc-64]], produced as a byproduct of [[depleted zinc oxide]] enrichment, would when neutron activated become zinc-65, which is a gamma emitter with a [[half-life]] of 244 days.<ref>{{cite web |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq1.html#nfaq1.6 |title=1.6 Cobalt Bombs and other Salted Bombs, Nuclear Weapons Archive, Carey Sublette |url-status=live |archive-url=https://web.archive.org/web/20120809054936/http://nuclearweaponarchive.org/Nwfaq/Nfaq1.html#nfaq1.6 |archive-date=2012-08-09 }}</ref>{{synthesis inline|reason=This reference does not say that this is the most effective use for area denial. In particular: The ref mentions fission-fusion-fission weapons in relation to salted bombs, not neutron bombs.|date=January 2023}}

== Hypothetical effects of a pure fusion bomb ==
{{see also|Inertial confinement fusion}}
With considerable overlap between the two devices, the prompt radiation effects of a [[pure fusion weapon]] would similarly be much higher than that of a pure-fission device: approximately twice the initial radiation output of current standard fission–fusion-based weapons. In common with all neutron bombs that must presently derive a small percentage of trigger energy from fission, in any given yield, a 100% pure fusion bomb would likewise generate a smaller atmospheric blast wave than a ''pure''-fission bomb. The latter fission device has a higher kinetic energy-ratio per unit of reaction energy released, which is most notable in the comparison with the D-T fusion reaction. A larger percentage of the energy from a D-T fusion reaction is inherently put into uncharged neutron generation as opposed to charged particles, such as the [[alpha particle]] of the D-T reaction, the primary species, that is most responsible for the [[coulomb explosion]]/fireball.<ref>{{Cite book|title=Physics of Societal Issues - Springer|language=en|doi=10.1007/978-0-387-68909-8|year = 2007|isbn = 978-0-387-95560-5|url = https://cds.cern.ch/record/1339081|last1=Hafemeister|first1=David}}</ref>

==List of US neutron weapons==
Anti-ballistic missile warheads
* [[W65 (nuclear warhead)|W65]] &mdash; Sprint enhanced radiation warhead developed by Livermore (cancelled)<ref name=UUR>{{Cite report| publisher = Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)| last = Josserand| first = Terry Michael| title = R&A for UUR_Weapon_History_Phases_20170206.| accessdate = 2021-07-24| date = 2017-03-01| osti = 1429158| url = https://www.osti.gov/biblio/1429158-uur_weapon_history_phases_20170206}}</ref><ref name=Sublette>{{Cite web| last = Carey Sublette| title = List of All U.S. Nuclear Weapons| work = Nuclear Weapon Archive| accessdate = 2022-06-24| url = http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html}}</ref>
* [[W66 (nuclear warhead)|W66]] &mdash; Sprint enhanced radiation warhead developed by Los Alamos (1975–1976)<ref name=UUR/><ref name=Sublette/>

Ballistic missile warheads
* [[W63 (nuclear warhead)|W63]] &mdash; Lance enhanced radiation warhead developed by Livermore (cancelled)<ref name=UUR/><ref name=Sublette/>
* [[W64 (nuclear warhead)|W64]] &mdash; Lance enhanced radiation warhead developed by Los Alamos (cancelled)<ref name=UUR/><ref name=Sublette/>
* [[W70]] Mod 3 &mdash; Lance enhanced radiation warhead developed by Livermore (1981–1992).<ref name=UUR/><ref name=Sublette/>

Artillery
* [[W79 Artillery-Fired Atomic Projectile|W79 Mod 0]] &mdash; {{convert|8|inch|adj=on}} enhanced radiation artillery shell developed by Livermore (1976–1992)<ref name=UUR/><ref name=Sublette/>
* [[W82]] Mod 0 &mdash; {{convert|155|mm|adj=on}} enhanced radiation artillery shell developed by Livermore (cancelled)<ref name=UUR/><ref name=Sublette/>

==See also==
* [[Atomic demolition munition]] – similar strategic use, low-yield nuclear weapons.
* [[Cobalt bomb]]
* [[Neutron transport]]
* [[Nuclear strategy]]
* [[Nuclear warfare]]
* [[Nuclear weapon design]]

== References ==
{{Reflist|30em}}

==Further reading==
* {{cite book |last1=Cohen |first1=Sam |author-link1=Samuel T. Cohen |date=1983 |title=The Truth About the Neutron Bomb: The Inventor of the Bomb Speaks Out |publisher=[[William Morrow and Company|William Morrow & Co.]] |isbn=978-0-688-01646-3}}
* {{cite book |last1=Cohen |first1=Sam |author-link1=Samuel T. Cohen |date=September 2015 |title=Shame: Confessions of the Father of the Neutron Bomb |url=http://www.athenalab.com/Shame_Confessions_of_the_Father_of_the_Neutron_Bomb_Sam_Cohen_2015_Fourth_Edition.pdf |archive-url=https://web.archive.org/web/20151023234100/http://www.athenalab.com/Shame_Confessions_of_the_Father_of_the_Neutron_Bomb_Sam_Cohen_2015_Fourth_Edition.pdf |url-status=dead |archive-date=2015-10-23 |edition=4th |access-date=2016-11-14 }}

== External links ==
* [https://web.archive.org/web/20081207101307/http://www.airpower.maxwell.af.mil/airchronicles/aureview/1979/jul-aug/snow.html Strategic Implications of Enhanced Radiation Weapons]
* [http://www.nuclearfiles.org/menu/key-issues/nuclear-weapons/basics/neutron-bomb.htm Nuclear Files.org] {{Webarchive|url=https://web.archive.org/web/20060614211140/http://www.nuclearfiles.org/menu/key-issues/nuclear-weapons/basics/neutron-bomb.htm |date=2006-06-14 }} Definition and history of the neutron bomb
* [http://forward.com/articles/134967/creator-of-neutron-bomb-leaves-an-explosive-legacy/ Creator of Neutron Bomb Leaves an Explosive Legacy]
* [https://www.wilsoncenter.org/nuclear-history-documents The Woodrow Wilson Center's Nuclear Proliferation International History Project] or NPIHP is a global network of individuals and institutions engaged in the study of international nuclear history through archival documents, oral history interviews and other empirical sources.

{{Authority control}}

[[Category:American inventions]]
[[Category:Energy weapons]]
[[Category:Neutron|Bomb]]
[[Category:Nuclear weapons]]

[[de:Kernwaffentechnik#Neutronenwaffe]]