Chapter 3
RESULTS and DISCUSSION
The calculated relative air density at Frenchman Flat for*?Shot Hamilton was 0.875, using ICAO
atmosphere as standard (15C and 760 mm Hg). The radiochemical yield measured by LASL
was 1.17 + 0.06 tons. This nuclear yield of about 1 ton was a twentieth of that expected; as a
result, all measurements were an order of magnitude lower than those anticipated during the
planning period before the shot—a significant fact in interpreting this data.
Where applicable, the total-dose measurements are presented as dose times slant distance
squared versus slant distance from ground zero with no corrections for relative air density.
Shot Hamilton was detonated on a 50-foot wooden tower.
3.1 INITIAL-GAMMA DOSE RATE
Data for initial-gamma dose rate was obtained at two of the three stations. No data was obtained by the instrumentation at 425 yards from ground zero. The reason for the failure of the
instrument is not known. Dose rate versus time for the remaining two stations is presented in
Figures 3.lL and 3.2.
The experimental and corrected data is presented in Table 3.1. The dose
rate data in these figures was corrected for fireball rise, taking into consideration the increase
in slant range from the detectors to the fireball (or cloud). The resulting dose rates are then
those that would be received from a stationary source. The data necessary to make the corrections for fireball rise was obtained from an EG&G film of the detonation.
Analysis of the film
showed that the fireball rise could be represented by:
h, == 23.5t 6.7
where h, is the cloud height in yards and t is the time after the detonation in seconds.
The curves for dose rate versus time obtained at both 550 and 750 yards exhibited a pronounced leveling off beyond H + 10 seconds (Figures 3.1 and 3.2). This effect resulted from a
characteristic of the instruments utilized for the measurements. To ensure successful documentation of the high dose rates anticipated in the time interval prior to 0.1 second for the
planned yield and to provide the necessary response time, the output frequency rangeof the
blocking oscillator circuit was raised (Section 2.2.1). This resulted in raising the-lower threshold of the instrument and caused the output frequéncy of the blocking oscillator circuit to gradually level off as the dose rates being measured passed through this threshold. The decrease in
actual yield from the anticipated yield by a factor of twenty resulted in the lower threshold of
the instruments being reached by both of the instruments before the entire + 40-second time
interval, which was to be documented, had elapsed. Consequently, the measured dose rates at
750 yards from ground zero lower than 1.5 x 107? r/sec and those at 550 yards lower than
5 x 107? r/sec were higher than the dctual intensities that reached those points.
An estimate of the probable decay from Shot Hamilton can be made by arbitrarily matching
the curve for intensity of the measured dose rate obtained at 750 yards with the curve obtained
from Shot Lassen, Operation Plumbbob, (Reference 4) at 1 second (Reference 16).
Figure 3.1
shows the manner in which the measured dose rate probably would have decayed, indicated by
the Lassen data points, had the instruments’ threshold not been reached. The excellent agreement between the two curves above 1.5 x 107? r/sec is apparent. A theoretical estimate of dose
rate versus time using data provided in AFSWC TR-58-13 is also indicated on Figure 3.1.
Figure 3.2 shows the gamma dose rate versus time measured at the 550-yard location, along
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