(December 19, 1997) In WISE NC 481; New Generations: The High Temperature Reactor, it was stated that plutonium isotopes other than plutonium-239 are unsuitable in nuclear weapons. We apologize: this is a regrettable, serious mistake.
(483/4.4799) WISE Amsterdam -Contrary to the popular belief that only the uneven plutonium isotopes are fissionable (and in nuclear reactors this might be true in general), in nuclear weapons ALL plutonium isotopes will fission, because of the presence of large numbers of fast neutrons. The division between "civil" or "military" plutonium is therefore an artificial one.
It is only because higher plutonium isotopes have shorter half-lives, decay sooner and thus produce more problematic neutrons and daughter products which do not fission and are more radioactive, and that the military prefer plutonium with 90% or more plutonium-239 for the production of nuclear weapons. Especi- ally the plutonium-241 isotope is nasty, because it has a short half-life of 13.2 years. It decays into americium-241 which emits heavy radiation.
Both the US and the UK have successfully tested nuclear weapons made from reactor-grade plutonium as mentioned already several times in the Newscommunique (i.e in the WISE 'MOX-Myth' special The MOX Myth: Plutonium grades - all pu is weapons-grade, 11 April 1997). Nuclear weapons made from reactor-grade plutonium, which contains only 65% plutonium-239, even need less conventional explosives to become critical, because they spontaneously emit neutrons and their yield is less. Manufacturing nuclear weapons made of reactor-grade plutonium is more troublesome. These nuclear weapons cannot be stored for two decades or more, like nuclear bombs made of "weapons-grade" plutonium. The conclusion is that all sorts of plutonium, so-called civil and military, are suitable for nuclear weapons and do have the same proliferation risks.
Source: Albright ea, Plutonium and Highly Enriched Uranium 1996. SIPRI, Oxford University Press, 1997, p.19.