estimated peak counts to dose rate for each of the three naturally occurring components of the total terrestrial gamma
radiation field.*
These conversion factors are given in Table
I.
The second method relates the "energy"
as defined previously
in three energy bands centered on the three above-mentioned
photopeaks (E ,, 1.32-1.60 MeV; Ez, 1.62-1.90 MeV; E3, 2.48-2.75
Mev)
to dose rate by means of three simultaneous equations:
T
0.41 (E3 - 0.60)
K 0.10 (Ey - 0.7 Eg - 0.5 E3 - 0.7)
U = 0.29 (E2 - 0.06 Ey - 0.93 E3 + 0.50)
where T, K, and U are the dose rates in ur/hr from the Th232
series, K4 , and the u238 series respectively.
The constants
in these equations were first obtained by applying a multiple
regression analysis to a large number of field spectra, using
the values of K, T, and U calculated from the peak area method.
In all three cases the correlation was very good,
tiating our methods of estimating peak area.
substan-
The magnitude of
the first coefficient of each equation, however,
is dependent
on the accuracy of our peak method conversion factors,
In the
case of the K and T equations, this coefficient can be obtained
independently in a manner analogous to that used in obtaining
the conversion factors for the peak method.
This was done and
the values obtained agreed to within 5% with those predicted
by the regression analysis.
The U coefficient could not be
calculated independently due to the significant contribution
to the Ep band in the field situation of scattered photons from
higher energy gamma rays of the uranium series,
Rough estimates
of this effect indicate that the coefficient of the U equation
obtained from the regression analysis is a reasonable one, This
band method has the advantage of being more amenable to routine
data analysis procedures and of providing more precise individual determinations of component dose rates.
Both the band and
peak methods agree very closely on the average.
Fallout Gamma
Two methods are also used for predicting the dose rate
from gamma emitting fallout radionuclides?
The first relates
the estimated areas of the two prominent fallout peaks at
0.75 Mev (Zr95-Nb95) and 0.51 MeV (Rut93_Rnl93, Ryl06_Rp106 |
-4e-