Cohen's parents were
Austrian Jews who emigrated from London, England. He was born on January 25, 1921, in
Brooklyn and raised in New York City. He studied mathematics and physics at
University of California, Los Angeles before joining the United States Army after the Japanese
attack on Pearl Harbor. 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. Cohen was personally responsible for recruiting the famous strategist
Herman Kahn into the
RAND Corporation. 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 development of the neutron bomb in 1978, but during
Ronald Reagan's presidency, Cohen claims to have convinced Reagan to make 700 neutron bombs, 350 shells to go into the 8 inch (200-millimeter) howitzer and 350 W70 Mod. 3 warheads for the
Lance missile.
"Clean" nuclear tests In 1956, President
Dwight D. Eisenhower announced the testing of a 95% "clean" (2-stage) fusion weapon, later identified to have been the July 11
Navajo test at Bikini Atoll during
Operation Redwing. This weapon had a yield of 4.5 megatons. 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. This is deliberate; the fusion reactions give off large quantities of 14.1 MeV neutrons, which have more energy than the 1.1 MeV "fission threshold" for U-238. This means the neutrons, which would otherwise escape, create fission reactions in the
neutron reflecting 'tamper', increasing the overall yield of the weapon essentially "for free". 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 July 12, 1958, the
Hardtack-Poplar shot of the
Mk-41C warhead was carried out on a barge in the lagoon yielded 9.3 megatons, of which only 4.8% was fission, and thus 95.2% "clean". In 1958, Cohen 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 one-tenth 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.
U.S. Department of Defense manual on the neutron bomb Cohen's neutron bomb is not mentioned in the unclassified manual by Glasstone and Dolan,
The Effects of Nuclear Weapons 1957–1977, 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). Under most atmospheric conditions no fallout effects would occur from the use of a neutron bomb, according to that manual, as the combination of 500-meter 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 in 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 controversially argued: "When we started this systems analysis business, we stepped through the looking glass where people did the weirdest things and (used) the most perverse kind of logic imaginable and yet claimed to have the most precise understanding of everything." ==Alleged support from the Pope for low-yield tactical nuclear bombs==