that the cessation times reported are closely related to the sensitivity of the measuring systems
used and the fallout levels observed.
Alt values for time of arrival given in Table 3.2 were determined from TOAD measurements.
They were obtained by subtracting the time interval measured by the instrumentclock, which
started when fallout arrived, from the total period elapsed between detonation and the time when
the instrument was read.
Because the TOAD’s were developed for use by the project and could not be proof-tested in
advance, certain operational problems were encountered in their use; these are reflected by
Footnotes §, f and jf in Table 3.2. Only Footnote f indicates that no information was obtained
by the units; however, Footnotes § and f are used to qualify questionable values. Because the
TOAD’s from the barge and island major stations were used elsewhere after Shot Flathead, Footnote * primarily expresses the operational difficulties involved in servicing the skiffs and keeping them in place.
The fact that a station operated properly and yet detected no fallout is indicated in both tables
‘by Footnote {. In the case of the major stations, this means that the TIR record showed no
measurable increase and all of the IC trays counted at the normal background rate. For the
minor stations, however, it means that the rate of arrival never exceeded 20 mr/hr per half
hour, because the radiation trigger contained in the TOAD wasset for this value.
3.2.3 Mass-Arrival Rate.
A measure of the rate at which mass was deposited at each of
the major stations during Shots Zuni and Tewais plotted in Figure 3.5 from data contained in
Table B.4; additional data are contained in Table B.6. Corresponding mass-arrival rates for
Shots Flathead and Navajo may be obtained, where available, by multiplying each of the IC-tray
activities (count/min’) in Figures 3.1 and 3.2 by the factor, micrograms per square feet per
hour per counts per minute per minute, [yg/(ft?-hr-count/min’)]. For the YAG 40, YAG 339,
and LST 611, the factor is 0.0524 for Shot Flathead and 0.7°1 for Shot Navajo. For the YFNB
29, the factor is 0.343 for Shot Flathead. For the YFNB 13 and How-F, the factor is 3.69 for
Shot Navajo.
The former values of mass-arrival rate, microgramsper square foot per hour [yg/(ft?/hr) ],
were calculated from the particle-size distribution studies in Reference 19, discussed in more
detail in Section 3.2.4. The number of solid particles in each size increment deposited per
Square foot per hour was converted to mass by assuming the particles to be spheres with a den-
Sity of 2.36 gm/cm*.
Despite the fact that a few slurry particles might have been present (Sec-
tion 3.3.1), these values were then summed, over all size increments, to obtain the total mass-
arrival rate for each tray, or a3 a function of time since detonation (TSD).
These results may
Rot be typical for the geographic locations from which the samples were taken, because of collector bias (Section 4.3.2).
Because this result will be affected by any discrepancy between the numberofparticles of
4 certain size, which would have passed through an equal area in free space had the tray not
been Present, and the number ultimately collected by the tray and counted, both sampling bias
(Section 4.3.2) and counting error (Section 3.2.4) are reflected in the curves of Figure 3.5. For
this reason they, like the curves of Section 3.2.1, are intended to provide only relative-rate in-
formation and should not be integrated to obtain total-mass values, even over the limited periods
When it would be possible to do so. The total amount of mass (mg/ft?) deposited at each major
station, determined from chemical analysis of OCC collections, is given in Table 3.16.
The constants to be used for the water-surface shots follow from the slurry-particle sodium
Chloride analyses in Reference 31 and were derived on the basis of experimentally determined
Values relating well-counter gamma activity to sodium chloride weight in the deposited fallout.
These values and the methods by which they were obtained are presented in Section 3.3.2. The
factors were calculated from the ratio of counts per minute per minute (count/min’) for the IC-
-fray area to counts per minute per gram [(counts/min)/gm] of NaCl from Table 3.12. The grams
of NaCl were convertedto grams of fallout, with water included, in the ratio of 1/2.2; and the
&4amma well counts from the table were expressed as end-window gamma counts by use of the
Tatio 1/62. An average value of specific activity for each shot was used for the ship stations,
45