Editing Effects of nuclear explosions (section)

== Indirect effects ==

=== Electromagnetic pulse ===
[[Gamma rays]] from a nuclear explosion produce high energy [[electron]]s through [[Compton scattering]]. For high altitude nuclear explosions, these electrons are captured in the [[Earth's magnetic field]] at altitudes between 20 and 40 kilometers where they interact with the Earth's magnetic field to produce a coherent [[nuclear electromagnetic pulse]] (NEMP) which lasts about one millisecond. Secondary effects may last for more than a second. The pulse is powerful enough to cause moderately long metal objects (such as cables) to act as antennas and generate high voltages due to interactions with the electromagnetic pulse. These voltages can destroy unshielded electronics. There are no known biological effects of EMP. The ionized air also disrupts radio traffic that would normally bounce off the [[ionosphere]].

Electronics can be shielded by wrapping them completely in [[Electrical conductor|conductive material]] such as metal foil; the effectiveness of the shielding may be less than perfect. Proper shielding is a complex subject due to the large number of variables involved. [[Semiconductors]], especially [[integrated circuits]], are extremely susceptible to the effects of EMP due to the close proximity of their [[p–n junction]]s, but this is not the case with thermionic tubes (or valves) which are relatively immune to EMP.  A [[Faraday cage]] does not offer protection from the effects of EMP unless the mesh is designed to have holes no bigger than the smallest wavelength emitted from a nuclear explosion.

Large nuclear weapons detonated at high altitudes also cause [[geomagnetically induced current]] in very long electrical conductors. The mechanism by which these geomagnetically induced currents are generated is entirely different from the gamma-ray induced pulse produced by Compton electrons.

=== Radar blackout===
{{See also|Nuclear blackout|Christofilos effect}}
The heat of the explosion causes air in the vicinity to become ionized, creating the fireball. The free electrons in the fireball affect radio waves, especially at lower frequencies. This causes a large area of the sky to become opaque to radar, especially those operating in the [[VHF]] and [[UHF]] frequencies, which is common for long-range [[early warning radar]]s. The effect is less for higher frequencies in the [[microwave]] region, as well as lasting a shorter time – the effect falls off both in strength and the affected frequencies as the fireball cools and the electrons begin to re-form onto free nuclei.<ref name=bethe>{{cite journal |last1=Garwin |first1=Richard L. |last2=Bethe |first2=Hans A. |title=Anti-Ballistic-Missile Systems |journal=Scientific American |date=1968 |volume=218 |issue=3 |pages=21–31 |doi=10.1038/scientificamerican0368-21 |jstor=24925996 |bibcode=1968SciAm.218c..21G }}</ref>

A second blackout effect is caused by the emission of [[beta particle]]s from the [[fission products]]. These can travel long distances, following the Earth's magnetic field lines. When they reach the upper atmosphere they cause ionization similar to the fireball but over a wider area. Calculations demonstrate that one megaton of fission, typical of a two-megaton H-bomb, will create enough beta radiation to blackout an area {{convert|400|km|miles}} across for five minutes. Careful selection of the burst altitudes and locations can produce an extremely effective radar-blanking effect.<ref name=bethe/> The physical effects giving rise to blackouts also cause EMP, which can also cause power blackouts. The two effects are otherwise unrelated, and the similar naming can be confusing.

=== Ionizing radiation ===
About 5% of the energy released in a nuclear air burst is in the form of [[ionizing radiation]]: [[Neutron radiation|neutrons]], gamma rays, [[alpha particle]]s and electrons moving at speeds up to the speed of light. Gamma rays are high-energy electromagnetic radiation; the others are particles that move slower than light. The neutrons result almost exclusively from the [[Nuclear fission|fission]] and [[Nuclear fusion|fusion]] reactions, while the initial gamma radiation includes that arising from these reactions as well as that resulting from the decay of short-lived fission products. The intensity of initial nuclear radiation decreases rapidly with distance from the point of burst because the radiation spreads over a larger area as it travels away from the explosion (the [[inverse-square law]]). It is also reduced by atmospheric absorption and scattering.

The character of the radiation received at a given location also varies with the distance from the explosion.<ref>{{cite journal |last1=Pattison |first1=J.E. |last2=Hugtenburg |first2=R.P. |last3=Charles |first3=M.W. |last4=Beddoe |first4=A.H. |title=Experimental Simulation of A-Bomb Gamma Ray Spectra for Radiobiology Studies |journal=Radiation Protection Dosimetry |date=2 May 2001 |volume=95 |issue=2 |pages=125–135 |doi=10.1093/oxfordjournals.rpd.a006532 |pmid=11572640 }}</ref> Near the point of the explosion, the neutron intensity is greater than the gamma intensity, but with increasing distance the neutron-gamma ratio decreases. Ultimately, the neutron component of the initial radiation becomes negligible in comparison with the gamma component. The range for significant levels of initial radiation does not increase markedly with weapon yield and, as a result, the initial radiation becomes less of a hazard with increasing yield. With larger weapons, above 50&nbsp;kt (200&nbsp;TJ), blast and thermal effects are so much greater in importance that prompt radiation effects can be ignored.

The neutron radiation serves to transmute the surrounding matter, often rendering it [[neutron activation|radioactive]]. When added to the dust of radioactive material released by the bomb, a large amount of radioactive material is released into the environment. This form of [[radioactive contamination]] is known as [[nuclear fallout]] and poses the primary risk of exposure to ionizing radiation for a large nuclear weapon.

Details of [[nuclear weapon design]] also affect neutron emission: the gun-type assembly [[Little Boy]] leaked far more neutrons than the implosion-type 21&nbsp;kt [[Fat Man]] because the light hydrogen nuclei (protons) predominating in the exploded TNT molecules (surrounding the core of Fat Man) slowed down neutrons very efficiently while the heavier iron atoms in the steel nose forging of Little Boy scattered neutrons without absorbing much neutron energy.<ref>{{cite web|url=http://glasstone.blogspot.com/2006/03/samuel-glasstone-and-philip-j-dolan.html|title=Credible effects of nuclear weapons for real-world peace: peace through tested, proved and practical declassified deterrence and countermeasures against collateral damage. Credible deterrence through simple, effective protection against concentrated and dispersed invasions and aerial attacks. Discussions of the facts as opposed to inaccurate, misleading lies of the "disarm or be annihilated" political dogma variety. Hiroshima and Nagasaki anti-nuclear propaganda debunked by the hard facts. Walls, not wars. Walls bring people together by stopping divisive terrorists.|website=glasstone.blogspot.com|access-date=30 March 2018}}{{self-published inline|date=March 2022}}</ref>

It was found in early experimentation that normally most of the neutrons released in the cascading chain reaction of the fission bomb are absorbed by the bomb case. Building a bomb case of materials which transmitted rather than absorbed the neutrons could make the bomb more intensely lethal to humans from prompt neutron radiation. This is one of the features used in the development of the [[neutron bomb]].

=== Earthquake ===
The [[Seismic wave|seismic pressure waves]] created from an explosion may release energy within nearby [[Plate tectonics|plates]] or otherwise cause an [[earthquake]] event. An underground explosion concentrates this pressure wave, and a localized earthquake event is more probable. The first and fastest wave, equivalent to a normal earthquake's [[P wave]], can inform the location of the test;<ref name="scientificamerican.com">{{cite web | url=https://www.scientificamerican.com/article/how-security-experts-track-north-koreas-nuclear-activity/ | title=How Security Experts Track North Korea's Nuclear Activity | website=[[Scientific American]] }}</ref> the [[S wave]] and the [[Rayleigh wave]] follow. These can all be measured in most circumstances by seismic stations across the globe, and comparisons with actual earthquakes can be used to help determine estimated yield via differential analysis, by the modelling of the high-frequency (>4&nbsp;Hz) teleseismic P wave amplitudes.<ref>{{cite journal | doi=10.1029/2019JB017418 | title=Yield Estimates for the Six North Korean Nuclear Tests from Teleseismic P Wave Modeling and Intercorrelation of P and Pn Recordings | journal=Journal of Geophysical Research: Solid Earth | date=May 2019 | volume=124 | issue=5 | pages=4916–4939 | last1=Voytan | first1=Dimitri P. | last2=Lay | first2=Thorne | last3=Chaves | first3=Esteban J. | last4=Ohman | first4=John T. | bibcode=2019JGRB..124.4916V | s2cid=150176436 | doi-access=free }}</ref><ref name="scientificamerican.com"/><ref>{{cite web|url=http://alsos.wlu.edu/information.aspx?id=2017|title=Alsos: Nuclear Explosions and Earthquakes: The Parted Veil|website=alsos.wlu.edu|access-date=30 March 2018|archive-url=https://web.archive.org/web/20120310191337/http://alsos.wlu.edu/information.aspx?id=2017|archive-date=10 March 2012|url-status=dead}}</ref> However, theory does not suggest that a nuclear explosion of current yields could trigger [[Fault (geology)|fault]] rupture and cause a major quake at distances beyond a few tens of kilometers from the shot point.<ref>{{cite web |url=http://seismo.berkeley.edu/seismo/faq/nuke_2.html |title=Nuke 2  |access-date=22 March 2006 |archive-url=https://web.archive.org/web/20060526133051/http://seismo.berkeley.edu/seismo/faq/nuke_2.html |archive-date=26 May 2006 |url-status=dead }}</ref>

=== Summary of the effects ===
The following table summarizes the most important effects of single nuclear explosions under ideal, clear skies, weather conditions. Tables like these are calculated from nuclear weapons effects scaling laws.<ref>[https://books.google.com/books?id=AOY9AQAAIAAJ Paul P. Craig, John A. Jungerman. (1990) ''The Nuclear Arms Race: Technology and Society'' p. 258]</ref><ref>[https://books.google.com/books?id=NO3626AOL9oC&pg=PA644 Calder, Nigel "The effects of a 100 Megaton bomb" ''New Scientist'', 14 Sep 1961, p. 644]</ref><ref>[https://books.google.com/books?id=Hckys7gpwl4C&pg=PA4 Sartori, Leo "Effects of nuclear weapons" ''Physics and Nuclear Arms Today'' (Readings from ''Physics Today'') p. 2]</ref><ref>{{cite web|url=http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html#nfaq5.1|title=Effects of Nuclear Explosions|website=nuclearweaponarchive.org|access-date=30 March 2018}}</ref> Advanced computer modelling of real-world conditions and how they impact on the damage to modern urban areas has found that most scaling laws are too simplistic and tend to overestimate nuclear explosion effects. The scaling laws that were used to produce the table below assume (among other things) a perfectly level target area, no attenuating effects from urban [[terrain masking]] (e.g. skyscraper shadowing), and no enhancement effects from reflections and tunneling by city streets.<ref>{{cite web|url=http://www.usuhs.mil/afrrianniversary/events/rcsymposium/pdf/Millage.pdf |title=Modeling the Effects of Nuclear Weapons in an Urban Setting |archive-url=https://web.archive.org/web/20110706161001/http://www.usuhs.mil/afrrianniversary/events/rcsymposium/pdf/Millage.pdf|url-status=dead|archive-date=6 July 2011|date=6 July 2011|access-date=30 March 2018}}</ref> As a point of comparison in the chart below, the most likely nuclear weapons to be used against countervalue city targets in a global nuclear war are in the sub-megaton range. Weapons of yields from 100 to 475 kilotons have become the most numerous in the US and Russian nuclear arsenals; for example, the warheads equipping the Russian [[Bulava]] submarine-launched ballistic missile ([[SLBM]]) have a yield of 150 kilotons.<ref>[http://en15.rian.ru/img/118575033_free.html The modern Russian Bulava SLBM is armed with warheads of 100–150 kilotons in yield.] {{webarchive |url=https://web.archive.org/web/20141006140135/http://en15.rian.ru/img/118575033_free.html |date=6 October 2014 }}</ref> US examples are the [[W76]] and [[W88]] warheads, with the lower yield W76 being over twice as numerous as the W88 in the US nuclear arsenal.

{| class="wikitable" style="font-size:95%; text-align:center;"
|+
! rowspan=2 | Effects
! colspan=4 | Explosive yield / height of burst
|-
! 1&nbsp;kt / 200&nbsp;m
! 20&nbsp;kt / 540&nbsp;m
! 1&nbsp;Mt / 2.0&nbsp;km
! 20&nbsp;Mt / 5.4&nbsp;km
|-
| colspan=6| '''Blast—effective ground range ''GR'' / km'''
|-
| Urban areas completely levelled ({{convert|20|psi|kPa|abbr=on|disp=or}})
| 0.2
| 0.6
| 2.4
| 6.4
|-
| Destruction of most civilian buildings ({{convert|5|psi|kPa|abbr=on|disp=or}})
| 0.6
| 1.7
| 6.2
| 17
|-
| Moderate damage to civilian buildings ({{convert|1|psi|kPa|abbr=on|disp=or}})
| 1.7
| 4.7
| 17
| 47
|-
| Railway cars thrown from tracks and crushed<br />(<!-- 0.63 kp/cm<sup>2</sup>= -->62&nbsp;kPa; values for other than 20&nbsp;kt are extrapolated using the cube-root scaling)
| ≈0.4
| 1.0
| ≈4
| ≈10
|-
| colspan=6 | '''Thermal radiation—effective ground range ''GR'' / km'''
|-
| [[Fourth degree burn]]s, [[Conflagration]]
| 0.5
| 2.0
| 10
| 30
|-
| [[Third degree burn]]s
| 0.6
| 2.5
| 12
| 38
|-
| [[Second degree burn]]s
| 0.8
| 3.2
| 15
| 44
|-
| [[First degree burn]]s
| 1.1
| 4.2
| 19
| 53
|-
| colspan=6 | '''Effects of instant nuclear radiation—effective slant range<sup>1</sup> ''SR'' / km'''
|-
| Lethal<sup>2</sup> total dose (neutrons and gamma rays)
| 0.8
| 1.4
| 2.3
| 4.7
|-
| Total dose for acute radiation syndrome<sup>2</sup>
| 1.2
| 1.8
| 2.9
| 5.4
|}

<sup>1</sup><small> For the direct radiation effects the slant range instead of the ground range is shown here because some effects are not given even at ground zero for some burst heights. If the effect occurs at ground zero the ground range can be derived from slant range and burst altitude ([[Pythagorean theorem]]).</small>

<sup>2</sup><small> "Acute radiation syndrome" corresponds here to a total dose of one [[Gray (unit)|gray]], "lethal" to ten grays. This is only a rough estimate since [[Relative biological effectiveness|biological conditions]] are neglected here.</small>

Further complicating matters, under global nuclear war scenarios with conditions similar to that during the [[Cold War]], major strategically important cities like [[Moscow]] and [[Washington, D.C.|Washington]] are likely to be hit numerous times from sub-megaton [[multiple independently targetable re-entry vehicles]], in a [[cluster bomb]] or "cookie-cutter" configuration.<ref>[https://ota.fas.org/reports/7906.pdf "The Effects of Nuclear War" Office of Technology Assessment, May 1979. pp. 42 and 44.] Compare the destruction from a single 1 megaton weapon detonation on Leningrad on page 42 to that of 10 clustered 40 kiloton weapon detonations in a 'cookie-cutter' configuration on page 44; the level of total destruction is similar in both cases despite the total yield in the second attack scenario being less than half of that delivered in the 1 megaton case</ref> It has been reported that during the height of the Cold War in the 1970s Moscow was targeted by up to 60 warheads.<ref>[https://books.google.com/books?id=Hckys7gpwl4C&pg=PA24 Sartori, Leo "Effects of nuclear weapons" ''Physics and Nuclear Arms Today'' (Readings from ''Physics Today'') p. 22]</ref> 

The reason that the cluster bomb concept is preferable in the targeting of cities is twofold: the first is that large singular warheads are much easier to neutralize as both tracking and successful interception by [[A-35 anti-ballistic missile system|anti-ballistic missile system]]s than it is when several smaller incoming warheads are approaching. This strength in numbers advantage to lower yield warheads is further compounded by such warheads tending to move at higher incoming speeds, due to their smaller, more slender [[physics package]] size, assuming both nuclear weapon designs are the same (a design exception being the advanced [[W88]]).<ref>
[https://books.google.com/books?id=x__CgnLTLqkC&pg=PA65 Robert C. Aldridge (1983) ''First Strike! The Pentagon's Strategy for Nuclear War'' p. 65]</ref> The second reason for this cluster bomb, or 'layering'<ref>{{cite web|url=http://www.acq.osd.mil/ncbdp/nm/nm_book_5_11/appendix_F.htm |title=The Nuclear Matters Handbook |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=2 March 2013 }}</ref> (using repeated hits by accurate low yield weapons) is that this tactic along with limiting the risk of failure reduces individual bomb yields, and therefore reduces the possibility of any serious collateral damage to non-targeted nearby civilian areas, including that of neighboring countries. This concept was pioneered by [[Philip J. Dolan]] and others.