NUCLEAR-DEBRIS FORMATION 31 1074 PHOTONS/SEC PER 10* FISSIONS 1075 1076 1077 1078 1079 107! 107"! TT — 107 !2 | it rc 10738 | | Pe My ttt rH 0.0 0.5 1.0 1.5 i u eed 2.0 2.5 PHOTON ENERGY, MEV Fig. 12—-Gamma-photon spectra from fission ete 3.0 3.5 4.0 products at various times after **U fission produced by athermonuclear neutron spectrum. The relative contributions of the important gamma-emitting nuclides to the total dose-rate have been plotted vs. time in Fig. 14. It is interesting to note that from a few days onward muchof the dose rate at any given time can be accounted for in terms of two or three nuclides and that volatilely behaving mass chains contribute prominently to the dose rate. The dose-rate contributions given here pertain, of course, to unfractionated debris. Since many of the hard emitters (e.g., cesium and iodine isotopes) are subject to fractionation, the relative dose-rate contributions will be greatly modified in the case of fractionated debris.