Calibration of
were placed over an array of dosimeters
ion chamber against a point 22625
at three sites on Bikini Island.
source,
A
the pressurized
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.
906 90y 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,
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
on the basis of these results,
pressurized ion chamber.
chamber results and the LiF gammaray exposure rates is presented in
Fig.
3.
A linear regression of the
two data sets gives agreement of
about 13% between the two methods.
One also finds that the correlation
of points in Fig.
as that in Fig. 2.
3 is not as good
This difference
is most likely due to the beta contribution to the LiF results, which
may vary throughout the islands,
lon chamber response — uR/h
whe,
thicknesses of aluminum absorbers
causing spread in the data.
0 wu
Departure from the 1:1 relationship
in Fig.
0
3 may be due to an over-
correction of the TLD data for beta
response or to insufficient
consideration of the ion chamber
data for energy dependence.
10
[Pot
20
30
40
50
60
70
80
LiF response — uR/h
Fig.
3.
Comparison of responses of
the pressurized ion chamber
with LiF TLD's.
The contri-
bution due to cosmic radiation
has been subtracted.