thicknesses of aluminum absorbers
Calibration of the pressurized
were placed over an array of dosimeters
ion chamber against a point 226),
at three sites on Bikini Island.
source,
A
the method used with the
feather analysis of the beta attenua-
instrument in this study, leads to
tion curves gave a maximum beta
about a 3% overestimate in the
energy between 1.5 and 2.2 MeV.
measurement of "typical" environmen~
Given the known predominance of
tal fields in this country.”
90.99, beta activities in the soil,
similar correction were made to
this energy range is consistent with
these data,
the 2.27 MeV 90, beta radiation.
independent exposure-rate
The analysis also revealed that the
determinations (ion chamber and LiF
average beta contribution to the
TLD) would be within 10%.
total LiF exposure rates was 27% --
considered to be satisfactory
a rather significant contribution.
agreement between the two reference
Therefore, it was necessary to reduce
techniques used in this work.
the LiF results by this amount to
Hence, on the basis of these results,
obtain the free-air gamma-ray
the NaI scintillation readings were
exposure rates.
normalized to the output of the
The comparison between the ion
If a
the agreement of the two
This is
pressurized ion chamber.
chamber results and the LiF gamma-
of points in Fig. 3 is not as good
as that in Fig. 2.
This difference
is most likely due to the beta con-
tribution to the LiF results, which
May vary throughout the islands,
causing spread in the data.
Departure from the 1:1 relationship
ain
S Oo
oO
6
5&5
One also finds that the correlation
Nn w
58
about 13% between the two methods.
—_
two data sets gives agreement of
oO
A linear regression of the
lon chamber response — uR/h
Fig. 3.
eo
Oo
ray exposure rates is presented in
a
0
response or to insufficient
30
i
40 50
tt
60 70
8
LiF response — uR/h
in Fig. 3 may be due to an overcorrection of the TLD data for beta
10 20
!
Fig. 3.
Comparison of responses of
the pressurized ion chamber
The contri-
consideration of the ion chamber
with LiF TLD's.
data for energy dependence.
has been subtracted.
bution due to cosmic radiation