632
FERBER
STEM-CLOUD PENETRATIONS
An RB-57 aircraft was available for stem-penetration missions
immediately following seven of the Dominic I detonations. The navigator
was provided with a dose rate meter with a range from 0.01 to 2000
mr/hr
and
was
instructed
to
record
the
dose
rate as the aircraft
penetrated the stem cloud at specified altitudes. The dose rates measured in the cockpit were then used to estimate the amount of activity
in the cloud.
The relation between cloud concentration and dose rate in a uni-
form infinite cloud? is given by
_ Dp
84p,
© = By (3.7 x 10°\(1.6 x 109E
where
(1)
C =cloud concentration, uc/cm?
D = dose rate, r/sec
Oy = standard density of air at sea level = 1.293 x 10° g/cm?
p = density of air at sampling altitude, g/cm?
-E = average gamma energy, Mev
84 = energy absorbed per roentgen, ergs per gram of air
1.6 x 10° ergs/Mev
3.7 x 104 = dis/sec per microcurie
If the unit of dose rate is converted to roentgens per hour and the concentration to megacuries per cubic mile,
c=2122
“po E
2
(2)
For stem penetrations within an hour after the burst, E was as-
sumed to be 1 Mev. For the sampling missions between 2 and 5 hr after
the burst, a value of 0.86 Mev was used.‘ Figure 2 gives the value of
p/P) as a function of altitude for a typical tropical atmosphere.’ With
the use of appropriate values for E and p/p) in Eq. 2, the dose rates
recorded during stem penetration were converted to cloud concentrations. An estimate of the stem diameter was then used to estimate the
total volume of cloud in a 1000-ft-thick layer. The total amount of activity in the layer and the fraction of the bomb represented by that
activity was then determined by multiplying the concentration by the
volume. The results are shown in Fig. 3 as a plot of the fraction of the
bomb present in a 1000-ft-thick layer of the stem cloud vs. height
(indicated
as percent
of the total stem height). The three highest
Dominic I data points are derived from the extended sampling missions
described later in this paper. The Redwing data used for the figure