CHAPTER 5 CHARACTERISTICS OF FALLOUT 5.1 GAMMA FIELD DECAY The decay rate for the gamma radiation from the fallout as measured in the field was analyzed from a theoretical as well as an experimental viewpoint, Data are presented on decay for Shots 1, 2, and 3. Since the capture to fission ratios have been reported as substantially the same for Shots 1 through 5# these data should be applicable to all five detonations. Their use on Shot 6 radioactive debris may be questionable. In general, the laboratory samples measured with ionization instruments in this study compare well with the field data read with an ionization survey meter, AN/PDR-T1B. The standard gamma decay constant, k = 1.2, that is presently used for nuclear detonations,is invalid for thermonuclear devices over the period from time zero until the contribution fror induced activities is insignificant as is evidenced by the following anai;sis. 5.1.1 Theoretical-and FieldLecay Theoretical beta (d/m) decay curves (Fig. 5.1) were constructed for Mike shot, IVY*# as well as for Shot 1, CASTLE,*#+ Data for these curves were calculated from the fission product decay and the reported capture to fission ratios of the important nuclides and were normalized to 10,000 fissions at 0 time.18/A& theoretical gamma decay curve based on the capture to fission ratiog from Shot 1 (Fig. 5.2) was also con- structed. The calculated curve gives the gamma energy 2migsion rate (Mev/min) from a radioactive source of Shot 1 composition as a function of time after detonation, It will correspomi to the experimental gamma Jonization decay curve if (a) the detector response is indepordent of energy (flat) at all ramma energies and (b) the geometry of the source, * * +t Private communication with N. Ballou, 0 =€=6By N.Ballou, USNRDL. By R. Cole, USNRDL. 50 %L.