the samples. In general, the land-surface shots deposited more coral than the watersurface shots, and the inverse relationship applied to sea water. There was rough correlation between fraction of the device and the fallout radiation level at the station.
3.5
RADIOCHEMICAL CHARACTERISTICS OF FALLOUT
Decay of the fallout activity was observed by measuring three separate activities:
beta disintegrations per minute, gamma photons, and gammaionization.
The measured
data are summarized in Figures 3.12, 3.13, and 3.14. The beta-decay curve was also
calculated by adding contributions from fission products and activities induced in device
components (Figure 3.15). These curves. were used to extrapolate activity measurements
to a commontime.
Radiochemical studies of the samples have yielded data on capture-to-fission ratios
and R-values. (R-values are an indication of the relative abundance of a particular nu-
clide as comparedto its normal abundancein fission products from slow-neutron fission
of U5, )
The most-important neutron-capture activities were due to Np*®, U3", and U2".
The R-values were measuredfor Sr®,
Ag!!!, calS, Bal” cel, nald?,
Sm!8 | Eu! | Gd! | and Tbe! using Mo” as a reference nuclide.
The measured capture-to-fission ratios are summarized in Table 3.2.
R-values for the cloud and fallout samples were consistent.
Usually, the
The R-values for the rare
earths Ag!!! and Cd!!5 were usually greater than unity, indicating an enrichmentof these
isotopes compared to slow-neutron fission products of U5. The R-values for Sr® were
usually less than unity. Detailed results are reported in the final reports of Projects
2.6a and 2.6b (see Appendix).
Two methods of performing material-balance calculations were used: (1) the fraction
of the device was computed using a radiochemical Mo’? determination as a tracer for the
number of fissions contributing to the sample and (2) the absolute beta count of a sample
was related to a calculation of beta activity of fission products and induced activities resulting from fission of a certain number of atoms at various times, as in Figure 3.15.
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