The Jasons and Nuclear War in Vietnam
Dr Peter Woit has an interesting blog post about the Jasons, a group of big-name particle physicists funded by DARPA (U.S. Department of Defense advanced research projects agency). One reference is to: 'Tactical Nuclear Weapons in Southeast Asia, by four authors including Freeman Dyson and Steven Weinberg...' It ignores Samuel Cohen's neutron bomb.
That report examines the use of air blast from large weapons to blow forest trees down to impede Viet Cong progress in the jungles, and the idea of laying down a fallout belt 200 miles wide. Naturally neither scheme was practical, and neither was the non-nuclear alternative which they recommended in other reports (an electronic fence consisting of air dropped sensors which would call in air attacks when people came near).
On Cosmic Variance, a petition of physicists to President Bush has been reported, pleading not to drop nuclear weapons on Iran. I hope they support civil defence.
'Samuel T. Cohen (born 1921 in Brooklyn, New York) is a physicist who is known for inventing the W70 warhead, the "enhanced neutron weapon" or neutron bomb, the blueprints of which were allegedly stolen by the Chinese .
'Samuel Cohen's parents came from London but he was brought up in New York. He received his physics PhD from UCLA. In 1944 he worked on the Manhattan project in the efficiency group and calculated how neutrons behaved in the Nagasaki weapon, Fat Man. At RAND Corporation in 1950, his work on the intensity of fallout radiation first became public when his calculations were included as a special appendix in Samuel Glasstone's book The Effects of Atomic Weapons.
'During the Vietnam War, Cohen argued that using small neutron bombs would end the war quickly and save many American lives, but politicians were not amenable to his ideas and other scientists ignored the neutron bomb in reviewing the role of nuclear weapons . He was a member of the Los Alamos Tactical Nuclear Weapons Panel in the early 1970s. President Carter delayed the neutron bomb in 1978, but during Reagan's presidency, Cohen claims to have convinced Reagan to make 700 neutron bombs, 350 shells to go into the 8 inch (200-millimetre) howitzer and 350 W70 warheads for the Lance missile .
'In 1956, President Eisenhower announced the testing of a 95% 'clean' (2-stage) fusion weapon, later identified to have been the 11 July Navajo test at Bikini Atoll during Operation Redwing. This weapon had a 4.5 megatons yield. Previous 'dirty' weapons had fission proportions of 50-77%, due to the use of uranium-238 as a 'pusher' around the lithium deuteride (secondary) stage. (The fusion neutrons have energies of up to 14.1 MeV, well exceeding the 1.1 MeV 'fission threshold' for U-238.) The 1956 'clean' tests used a lead pusher, while in 1958 a tungsten carbide pusher was employed. Hans A. Bethe supported clean nuclear weapons in 1958 as Chairman of a Presidential science advisory group on nuclear testing :
' "... certain hard targets require ground bursts, such as airfield runways if it is desired to make a crater, railroad yards if severe destruction of tracks is to be accomplished... The use of clean weapons in strategic situations may be indicated in order to protect the local population." -Dr Hans Bethe, Working Group Chairman, 27 March 1958 "Top Secret - Restricted Data" Report to the NSC Ad Hoc Working Group on the Technical Feasibility of a Cessation of Nuclear Testing, p 9.
'In consequence of Bethe's recommendations, on 12 July 1958, the Hardtack-Poplar shot on a barge in the lagoon yielded 9.3 megatons, of which only 4.8% was fission. It was 95.2% clean. It was the clean Mk-41C warhead.
'Cohen in 1958 investigated a low-yield 'clean' nuclear weapon and discovered that the 'clean' bomb case thickness scales as the cube-root of yield. So a larger percentage of neutrons escapes from a small detonation, due to the thinner case required to reflect back X-rays during the secondary stage (fusion) ignition. For example, a 1-kiloton bomb only needs a case 1/10th the thickness of that required for 1-megaton.
'So although most neutrons are absorbed by the casing in a 1-megaton bomb, in a 1-kiloton bomb they would mostly escape. A neutron bomb is only feasible if the yield is sufficiently high that efficient fusion stage ignition is possible, and if the yield is low enough that the case thickness will not absorb too many neutrons. This means that neutron bombs have a yield range of 1-10 kilotons, with fission proportion varying from 50% at 1-kiloton to 25% at 10-kilotons (all of which comes from the primary stage). The neutron output per kiloton is then 10-15 times greater than for a pure fission implosion weapon or for a strategic warhead like a W87 or W88 .
'Cohen's neutron bomb is not mentioned in the unclassified manual by Glasstone and Dolan, The Effects of Nuclear Weapons 1957-77, but is included as an 'enhanced neutron weapon' in chapter 5 of the declassified (formerly secret) manual edited by Philip J. Dolan, Capabilities of Nuclear Weapons, U.S. Department of Defense, effects manual DNA-EM-1, updated 1981 (U.S. Freedom of Information Act).
'Provided that the weapon was not used in a thunderstorm, no fallout effects would occur from the use of a neutron bomb according to that manual, as the combination of 500 m burst altitude and low yield prevents fallout in addition to significant thermal and blast effects. The reduction in damage outside the target area is a major advantage of such a weapon to deter massed tank invasions. An aggressor would thus be forced to disperse tanks, which would make them easier to destroy by simple hand-held anti-tank missile launchers.
'Cohen's backing of investigations into these controversial ideas won him some media attention after many years of being ignored. In 1992 he was featured on the award-winning BBC TV series Pandora's Box episode, To the Brink of Eternity, discussing his battles with officialdom and colleagues at the RAND Corporation.
'Cohen stated that he "worked in France on low-yield, highly discriminate tactical nuclear weapons in 1979-1980".
"In 1979, Pope John Paul II conferred on one of the authors (Sam Cohen) a peace medal for his invention, the neutron bomb. This was a small nuclear weapon designed to do its work, killing enemy military forces, without destroying a country’s infrastructure." (Cohen, March 11, 2003)
The Pope, John Paul II, was from Poland and knew that Warsaw Pact forces had a massive tank superiority in Europe (though NATO maintained an overall strategic superiority), and that a deterrent which was designed to minimise civilian casualties was a step away from the risk of indiscriminate warfare. The neutron bomb's killing by neutron radiation is different from from the fallout of a normal high yield thermonuclear weapon because it can be controlled more precisely, restricted to military targets and kept away from civilians.
'In 1981, the Christian Science Monitor reported that there "are 19,500 tanks in the Soviet-controlled forces of the Warsaw Pact aimed at Western Europe. Of these, 12,500 are Soviet tanks in Soviet units. NATO has 7,000 tanks on its side facing the 19,500." (Joseph C. Harsch, "Neutron Bomb: Why It Worries The Russians," Christian Science Monitor, August 14, 1981, p. 1.) 
'The speed of modern warfare meant that the civilian population would be unlikely to withdraw from combat zones and would suffer a large number of deaths in a nuclear war where the blast yields and fallout were significant. Because neutron bombs do not produce the indiscriminate blast (only 6 psi at ground zero from a 1 kt blast yield detonation at 500 m altitude, and only 1 psi at 2 km distance), heat and fallout damage of other nuclear weapons, they were more credible as a deterrent to Soviet tanks. However, many people believed that the very deployment of the neutron bomb threatened an escalation to full scale nuclear retaliation, thus canceling out the supposed benefits. Advances in precision anti-tank weapons ultimately made the neutron bomb redundant tactically in its original objective. The debate over clean low yield nuclear weapons continues with earth penetrator technology, however.
'Hans A. Bethe, Working Group Chairman, originally Top Secret - Restricted Data Report of the President's Science Advisory Committee, 28 March 1958, defending on pages 8-9 'clean nuclear weapons tests', online
Terry Triffet and Philip LaRiviere, Characterization of Fallout, Operation Redwing fallout studies, directly comparing contamination from two 'dirty' tests (Tewa and Flathead) to two 'clean' tests (Navajo and Zuni), online
Christopher Ruddy, Bomb inventor says U.S. defenses suffer because of politics, June 15, 1997 online
Charles Platt, Profits of Fear, August 16, 2005 online here and here in other formats
Sam Cohen and Joseph D. Douglass, Jr, "The Nuclear Threat That Doesn't Exist – or Does It?", March 11, 2003, online; Red mercury, fusion-only neutron bombs, Russia, Iraq, etc
---- North Korea's Nuclear Initiative, April 28 2004 online
---- Development of New Low-Yield Nuclear Weapons, March 9, 2003, online
---- The Rogue Nuclear Threat, April 26, 2002, online
Joe Douglass, The Conflict Over Tactical Nuclear Weapons Policy in Europe (1968)
William R. Van Cleave & S. T. Cohen, Nuclear Weapons, Policies, and the Test Ban Issue, 1987, ISBN 0275923126
Samuel T. Cohen, We Can Prevent World War III, 1985, 2001, ISBN 0915463105
---- The Truth About the Neutron Bomb: The Inventor of the Bomb Speaks Out, William Morrow & Co., 1983, ISBN 0688016464
---- Shame: Confessions of the Father of the Neutron Bomb (2000), ISBN 0738822302, memoir
---- & Marc Geneste, Echec a La Guerre : La Bombe a Neutrons, Copernic, 1980 
Sherri L. Wasserman, The Neutron Bomb Controversy: A Study in Alliance Politics, Praeger, 1983 
Review of Shame published on Amazon: '
ARE EARTH PENETRATORS A CLEAN ALTERNATIVE TO HIGH YIELD SURFACE BURST NUCLEAR WEAPONS?
A few scientific facts about the earth penetrator. A 1-kiloton nuclear explosion at a depth of just 1 metre produces crater effects equivalent to that from a 25 kiloton surface burst. This massive enhancement occurs because most of the energy that is released blast and heat flash from a surface burst is coupled into the ground if the burst is at even a slight depth. For even slight depths, the x-rays and the bomb case shock are absorbed by the ground. Hence you achieve two things at once: you cut down heat flast and blast greatly, and you use that energy (which otherwise would be wasted in politically inexpedient collateral damage) to destroy your enemy's hardened underground structure. For a U.S. Army analysis see DOES THE UNITED STATES NEED TO DEVELOP A NEW NUCLEAR EARTH PENETRATING WEAPON? online by Thomas F. Moore: 'The determination is that the US does need a new nuclear earth-penetrating weapon and offers recommendations for the path forward.' See also the 2003 U.S. Army review by John Welsh, NUCLEAR DETERRENCE IS HERE TO STAY, also online: 'a national missile defense system may enhance our security against rogue states, but can not replace nuclear weapons; that terrorist and non-state actors can be deterred through deterrence by denial; that we should develop smaller yield nuclear weapons (despite large infrastructure concerns), and that we should NOT reduce the size of our nuclear arsenal to that of a minor nuclear power.'
In any case, the U.S. Armed Forces Radiobiology Research Institute (Bethesda, Maryland) in 2003 published the 2nd edition of a detailed handbook, MEDICAL MANAGEMENT OF RADIOLOGICAL CASUALTIES, available online.
Nuclear testing evidence
America did a shallow underground test in 1951, 1.2 kiloton Uncle which was detonated at 5.2 metres depth in Nevada soil. You can get an enhancement of residual radiation doses and you get a base surge, similar to the column collapse dust cloud from underwater bursts, except it is composed of the bulk subsidence of sand and dust instead of dense mist. Because it rolls out quickly from the base of the collapsing column (hence the term 'base surge'), it causes an early transit radiation exposure. However a 1-kiloton burst at just 1 metre depth will not create a significant base surge.
In the first British test, Hurricane, a very shallow burst however there was no significant base surge, although the slight depth of burst burst (2.7 metres below the waterline inside a ship) was enough to reduce the thermal energy emission to just 2% of the explosion yield (this figure is about 20% for a surface burst or 35% for an air burst). A surface burst does not produce a base surge. Base surges are optimised for shallow, not very shallow depthsYou would need to detonate a 1-kiloton bomb at a depth of at least 5 metres to create a base surge of importance. Shallower bursts would create the desired destructive effects without enhancing the residual radioactivity by significant base surge formation.
The fallout pattern for a 1-kiloton near surface burst is very small, and the fallout is deposited in massive visible particles where the dose rate is dangerous. See Dr Carl F. Miller, USNRDL-466 page 17 for the mass deposit of fallout associated with 1.2 kt Nevada surface burst S-shot and underground or Uncle U-shot, 1951. Fallout patterns from 1 kiloton surface bursts and shallow buried bursts show that the serious fallout radiation hazards occur a few hundred metres around ground zero upwind and 1-2 km downwind, so people seeing fallout can simply walk away as the time to do so is short compared to the time taken to accumulate a serious dose.
If the fission yield could be reduced by deriving part of the energy from fusion, this would reduce the residual radiation problem still further (although the contribution from neutron capture nuclides like Al-28, Mn-56 and Na-24 in soil increases in 'cleaner' weapons, it is still small compared to the fission product radiation in fallout). The fallout pattern scaling scheme given by Glasstone and Dolan is based on getting straight line approximations for 10 kt to 1 Mt yield portions of curves plotted in Dolan's DNA-EM-1 for DELFIC (Defence Land Fallout Interpretative Code) fallout calculations, and exaggerate the calculations for low yields of say 1 kiloton. The actual calculations and the fallout data from tests indicate less of a hazard that Glasstone and Dolan indicate for 1-kiloton surface bursts. I'll compare the Sugar fallout pattern with Glasstone and Dolan's inaccurate simplified data in a later post, and will discuss a fallout prediction model which works.