236
LOWDER, BECK, AND CONDON
a
A, COLORADO SPRINGS, COLO., OCT. 11, 1962
B, ARGONNE, ILL., OCT. 15, 1962
_
0.75 MEV
957 — Nb
104 F—
4
3 1er
aan
Ww
2
O
W
2.62 MEV
2087|
12
ifL
_
Let
20
| tt tN
60
100
140
180
220
260
CHANNEL NUMBER
Fig. 2—Tuo typical field spectra obtained during late 1962. The cosmic, natural-gamma, and fallout-gamma levels are all somewhat higher
at location A.
absorption peaks, at 0.5 Mev (!4°Ba—‘!°La, !Ru, and Rh), 0.75 Mev
(5Zr—*Nb), 1.46 Mev (!°K), and 2.62 Mev (79871), as well as other
minor peaks, including the 1.76 Mev *!*Bi peak. By a determination of
the area under these peaks or of the total number of counts in energy
bands bracketing them, estimates can be made of the contribution from
each emitter or series of emitters to the total dose rate in air at 1m
aboveground.
In the former method the area under each total-absorption peak is
approximated by asSuming a linear continuum under the peak on semilog paper, fit to the values on each side. This area, although not necesSarily identical to the true number of total-absorption counts, is as-
sumed to be directly proportional to the incoming flux of primary
photons. This has been satisfactorily checked in the laboratory for several energies and over a wide range of flux values. If a uniform source
distribution in the soil for the naturally occurring radioisotopes and an
exponential distribution for fallout emitters are assumed, the flux and