French nuclear tests at-Mururoa

摘要

SIR - In connection with your news report about French nuclear tests at Mururoa Atoll (Nature 377, 91-92; 1995), I should like to clarify the Greenpeace assertion about traces of caesium-134 ("a known product of nuclear fission") indicating leakage ofradioactivity around the atoll from past French underground nuclear tests. This is very doubtful. Caesium-134 is not a direct product of nuclear fission, but is created from cae-sium-133 by the absorption of a neutron. As a consequence, caesium-134 is not Significantly produced in a nuclear explosion, but is produced in prodigious quantities in nuclear reactors. (See Table 1.3 of Radioactivity after Chernobyl SCOPE 50, edited by Warner and Harrison, in which radioactive releases from nuclear detonations and nuclear reactor accidents are compared.) Indeed, one of the first tests undertaken of a radioactive plume is to examine it for the presence of caesium-134 to establish if the source was a weapon or a reactor. This was done, for example, by the Swedes in 1986 when they were the first in the West to announce the reactor accident at Chernobyl.