RADIOACTIVITY VS. HEIGHT IN NUCLEAR CLOUDS
635
penetration, and then dropped sharply. (It would be advantageous to
use automatic time—intensity recorders in future operations.)
The effect of aircraft shielding on the dose rate in the cockpit is
also uncertain. Tests made at the ground, using a point source outside
the aircraft, indicated that there was no appreciable shielding effect
on gamma radiation by the aircraft. Equation 2 assumes that the receptor is completely surrounded by a uniform radiation field. Actually,
of course, the receptor was surrounded by a“ blank space” equivalent
to the volume of the aircraft. No attempt has been made to correct for
this. However, the effect should be small, probably less than a factor
of 2, since the mean free path of the gamma radiation is large compared to the dimensions of the aircraft. Experimental determination of
the correction factor should be planned in connection with any future
operation of this type.
AIRCRAFT SAMPLING IN THE VICINITY OF THE CLOUD BASE
Aircraft equipped with Los Alamos Scientific Laboratory airfilter tanks were used for sampling after five Dominic I detonations.
Approximately 1l-hr sampling missions were flown at altitudes from
35,000 to 48,000 ft at 2 to 5 hr after detonation. The two sampling
tanks were opened simultaneously when contact with the cloud was
made and remained open for the entire Sampling period, As the sampling patterns were flown, readings in the cockpit were made at 1l-min
intervals with a hand-held AN/PDR-27J Radiacmeter capable of mea-
suring activity in a range from 0.01 to 500 mr/hr. Sampling missions
were successful after four of the five detonations. The radiochemical
analyses of the samples are reported elsewhere.°
The dose-rate readings obtained during three extended sampling
missions were sufficient for estimations of the distribution and the
amount of activity in the clouds at the sampling altitudes. Similar
analyses were done for all three missions. The results are included in
Fig. 3.
One of the clouds was sampled at an altitude of 45,000 ft at approximately 3 to 4 hr after detonation. The base of the cloud was reported
to be at about 45,000 ft. Both the shot-time wind data and the position
of the cloud indicate east-southeast cloud travel at about 15 knots, For
correction for the movement of the cloud during the sampling period,
the reported aircraft positions were adjusted to the sampling midtime
of 3), hr after detonation, The corrected radiation field and the actual
unadjusted sampling track are shown in Fig. 4. If a decay exponent of
—1.2 is assumed, integration of the pattern yields 520 r/hr-cu mi
at 1 hr in a 1000-ft-thick layer, From Eq.2 this is equivalent to 270
Mc, or 4.9 x 107* of the total fission products produced by the detona-