The spontaneous fission half-life of 240Pu

Abstract

A value for the spontaneous fission half-life of 240Pu has been obtained from the measured neutron emission rates of four relatively large 240Pu neutron sources (∼10 5–10 3 n/sec) and their known masses, compositions and multiplications. The four sources are the Aldermaston primary and two substandards and the Harwell standard, all of which have been recently calibrated to an accuracy of better than 1 per cent. The ‘best value’ of the average number of neutrons per fission, ν , for 240Pu is discussed in arriving at a final mean half-life of (1· ± 0·025) × 10 11 yr. The present determination is compared with other published measurements obtained by the more conventional technique of counting fission fragments from thin foils.