ity of the short-lived nuclide with no daughters present on day 26 to the known activity of a nuclide which had been observed on day 26 and had fractionated in the same fashion as the unknown. Fractionation was based on the behavior of iso- topes of the unknown which were present on day 26. If no isotope was present on day 26 then an isotope of an isobaric precursor of the unknown was chosen to represent the fractionation behavior of the unknown. The equation used to relate a short-lived nuclide to a reference nuclide was Ba By As Ap An ’ (3) where A activity per unit area of nuclide A at time t post detonation, B # activity per unit area of nuclide B at time t post detonation, Ag ™ decay constant of nuclide A, Ap * decay constant of nuclide B, A, = number of A atoms per unit fission at time t, B, ™ number of B atoms per unit fission at time t. The quantity AL or BL was calculated using 1) first order lin- ear kinetics equations, 2) fission yields for 14 MeV fission obtained from the evaluated nuclear data files of the National Nuclear Data Center (EN82), and 3) branching fractions and decay schemes from the seventh edition of the Table of Isotopes (Le78). Since each nuclide accounted for was the nth member of an isobaric chain, the number of atoms at time t would increase or decrease relative to the number at time of detonation due to decay and ingrowth phenomenon of precursor isobars. The exceptions were the few products arising from short- lived neutron emitting precursors. This decay and ingrowth phenomenon was accounted for by Eq. 4 which was originally described by Bateman (Bal0O) and later recast in a more general form by Skrable (Sk75). 18