Editing Neutron bomb (section)

==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 found in nature (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; however, 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}}