4.3.6 Radiochemistry-Spectrometry Comparison. Calibrated spectrometer measurements on samples of known fission content allow expected counting rates to be computed for the sam- ples in any gammacounter for which the response is simply related to the gross photon frequency and energy. Accordingly, the counting rate of the doghouse counter was computed for the stang_ ard-cloud samples by application of the calibration curve (Reference 43) to the spectral lines -and frequencies reported in Reference 57 and reproduced in Table B.20. These results are compared with observations in Table 4.11, as well as with those obtained previously using radiochemical-input information with the same calibration curve. Cloud samples were chosen, because the same physical sample was counted both in the spectrometer and doghouse counter, thereby avoiding uncertainties in composition or fission content introduced by aliquoting or other handling processes. Several of the spectrometers used by the project were uncalibrated, that is, the relation between the absolute number of source photons emitted per unit time at energy E and the resulting pulse-height spectrum was unknown. A comparison method of analysis was applied in these cases, requiring the area of a semi-isolated reference photopeak, whose nuclide source was known, toward the high-energy end of the spectrum. From this the number of photons per sec- onds per fissions per area can be computed. The area of the photopeak ascribed to the induced product, when roughly corrected by assuming efficiency to be inversely proportional to energy, yields photons per seconds per fissions. The latter quantity leads serially, via the decay Scheme, to disintegration rate per fission at the time of measurement to atoms at zero time per fission, which is the desired product/fission ratio. The’ hine at 0.76 Mev provides a satisfactory reference from ~ 30 days to 2 years, but the gross spectra are usually not simple enough to permit use of this procedure until an age of ~ % year has been reached. A few tracings of the recorded spectra appear in Figure 4.15, showing the peaks ascribed to the nuclides of Table 3.20. Wherever possible, spectra at different ages were examinedto in- sure proper half-life behavior, as in the Mn*illustration. The Zuni cloud-sample spectrum at 226 days also showed the 1.7-Mevline of Sb'*‘, though not reproduced in the figure. This line was barely detectable in the How Island spectrum, shown for comparison, and the 0.60-Mev line of Sb'™4 could not be detected at all. Average energies, photon-decay rates and other gamma-ray properties have been computed from the reduced spectral data in Table B.20 and appear in Table B.21. 4.3.7 Air Sampling. As mentioned earlier, a prototype instrument known asthe high volume filter (HVF) was proof-tested during the operation on the ship-array platforms. This instrument, whose intended function was incremental aerosol sampling, is described in Section 2.2. All units were oriented fore and aft in the bow region of the platform between the two IC’s shown in Figure A.1. The sampling heads opened vertically upward, with the plane of the filter horizontal, and the airflow rate was 10 ft/min over filter area of 0.0670 ft?, producing a face velocity of 1.7 mph. The instruments were manually operated according to a fixed routine from the secondary control room of the ship; the first filter was opened when fallout was detected and left open until the TIR reading on the deck reached ~1 r/hr; the second through the seventh filters were exposed for '/,-hour intervals, and the last filter was kept open until it was evident that the fallout rate had reached a very low level. This plan was intended to provide a sequence of relative air concentration measurements during the fallout period, although when 1 r/hr was not reached only one filter was exposed. Theoretically, removal of the dimethylterephalate filter material by sublimation will allow recovery of an unaltered, concentrated sample; in practice however, the sublimation process is so slow that it was not attempted for this operation. After the sampling heads had been returned to NRDL,thefilter material containing the activ- ity was removed as completely as possible and measured in the 4-7 ionization chamber; these data are summarized in Table B.36. It may be seen that the indicated arrival characteristics generally correspond with those shown in Figures 3.1 to 3.4. A comparative study was also made for someshots of the total numberof fissions per square foot collected by HVF’s, IC’s, and OCC’s located on the sameplatform. lIonization-chamber 122