-6The Nectar test (May 14, 1954) was used as the date of origin except where otherwise indicated, but earlier shots also contributed radioactivity to the samples studied. Especially the Bikini (March 1, 1954) shot contributed greatly to some of the samples. Residual long-lived products from earlier detonations prior to 1954 rendered the curves less steep than they would have been as a result of the 1954 series alone. The trends of activity as related to time are of two kinds, the physical decay of individual samples, and the rate of change in activity of a certain type of sample at a certain locality. To distinguish it from physical decay, referred to tn this report as decline. the latter trend will be Results are shown as graphs of the relationship of logarithm of radioactivity to logarithm of time of collection after detonation. The date of origin used may deviate somewhat from detonation day or the true origin without markedly affecting linearity of the plot over the period of study. The slope is changed according to the date of origin selected, but if the same origin is used for both decay and decline, the two may be compared. Hunter and Ballou (1951) show on logarithmic plot the theoretical decay of mixed slow-neutroninitiated fission products of U-235 over & period from 1 to 1000 days as a slightly curving line with a predomi- nantly below) downward curvature (concave and a general slope varying reef " ] decline and decay as becoming more or less steep with the passage of time, and when the terms steepening or leveling are applied to the trends, the log-log relationship is implied. A single half life when plotted semilogarithmically gives a straight line, while on the same plot a mixture of half lives results in @ line of —i. ~ — Gress Radioactivity a In log-log graphs it will be convenient to speak of slopes or rates of + radioactivity observed in the present study facilitates comparison with this curve and within the study itself. ~ * T from -1.0 to -1.7, averaging -1.2 (Fig. 2). A similar presentation of the trends of Fig. 2 m 4 ots Denys «fier vternavtron Reston af NL Fig. 2. Mixed fission product decay, gross beta. (After Hunter -and Ballou). increasing steepness. In the declines shown as straight lines on log-log plots possible fluctuations of a cyclic nature attributable to season or other variables are ignored.