able for each ship and shot (Figure B.1), dividing the data into appropriate intervals on the basis of the plots, and calculating the slopes of the least-squares lines for these intervals. The maximum depths of penetration listed in Table 3.4 were derived from the same plots by establishing that the slopes did not differ significantly from zero outside of the selected intervals. Erratic behavior or failure of the probes on both ships during Shot Zuni and on the YAG 40 during Shot Flathead prevented the taking of data which could be used for equivalent-depth determinations. It did prove possible in the former case, however, to trace the motion of the deepest tip of the activity profile from the YAG 39 measurements; and this is reported, with corresponding values from the other events, as a2 maximum penetration rate in Table 3.5. it is important to emphasize that the values given in Tables 3.3 and 3.4, while indicating re- markably uniform penetration behavior for the different kinds of events, refer only to the gross body of the fallout activity as it gradually settles to the thermocline. When the deposited material consists largely of solid particles, as for Shots Zuni and Tewa, it appears that some fast penetration may occur. The rates listed for these shots in Table 3.5 were derived from a fasttraveling component which may have disappeared below the thermocline, leaving the activity profile open at the bottom (Figure 3.10). On the other hand, no such penetration was observed for Shot Flathead and was questionable in the case of Shot Navajo. This subject is discussed further in Section 4.3.2, and estimates of the amountof activity disappearing below the thermocline are presented. - It is also important to note that the linear penetration rates given in Table 3.3 apply only from about the time of peak onward and after the fallout has penetrated to a depth of from 10 to 20 meters. Irregular effects at shallower depths, like the scatter of data points in the vicinity of the thermocline, no doubt reflect the influence both of differences in fallout composition and uncon- trollable oceanographic variables. The ships did move during sampling and may have encountered nonuniform conditions resulting from such localized disturbances as thermal gradients, turbulent regions, and surface currents. In addition to penetration behavior, decay and solubility effects are present in the changing activity profiles of Figure 3.10. The results of the measurements made by the decay probe (SIO-D) suspended in the tank filled with ocean water aboard the YAG 39 are summarized in Table 3.6. Corresponding values from Reference 15 are included for comparison; although similar instrumentation was used, these values were derived from measurements made over slightly different time intervals in contaminated water taken from the ocean some time after fallout had ceased. Two experiments were performedto study the solubility of the activity associated with solid fallout particles and give some indication of the way in which activity measurements made with energy-dependent instruments might be affected. Several attempts were also made to make di- rect measurements of the gamma-energy spectra of water samples, but only in one case (Sample YAG 39-T-IC-D, Table B.20) was there enoughactivity present in the aliquot. The results of the experiments are summarized in Figures 3.11 and 3.12. Two samples of particles from Shot Tewa, giving 4-7 ionization chamber readings of 208 x 107 *® and 674 x 107° ma respectively, were removed from a single OCC tray (YAG 39-C-34 TE) and subjected to measurements designed to indicate the solubility rates of various radionuclides in relation to the overall solubility rate of the activity in ocean water. The first sample (Method I) was placed on top of a glass-wool plug in a short glass tube. A piece of rubber tubing connected the top of this tube to the bottom of a 10-ml microburetfilled with sea water. The sea water was passed over the particles at a constant rate, and equivolume fractions were collected at specified time intervals. In 23 seconds, 3 ml passed overthe particles, corresponding to a settling rate of 34 cm/min-—-approximately the rate at which a particle of average diameter in the sample (115 microns) would have settled. The activity of each fraction was measured with the well counter soon after collection and, when these measurements were combined with the total sample activity, the cumulative percent of the activity dissolved was computed (Figure 3.11). Gamma-energy spectra were also measured on fractions corresponding roughly to the beginning (10 seconds), middle (160 seconds) and end (360 seconds) of the run (Figure 3.12). The time of the run was D+5 days. 48