(No/%), the ratio of estimated absorption peak counts to
primary flux for axial incidence,
was determined in the
laboratory for several energies using standard 137cs, 24Na,
113sn, and 226Ra sources and for other energies by comparison
with our previously well calibrated 5" x 3" detector using
40x,
85sr
and
232qh
sources of unknown
intensity.
These
results are given in Table I.
(NF/No), the angular correction factor for 0.61 MeV
and for 1.76 MeV y-rays was obtained by numerical integration
over the measured angular response of the detector for these
energies and the calculated angular primary flux distribution
from a uniformly distributed source.
The measured angular
response of the 4" x 4" detector to y-rays of these energies
was much flatter than for the 5" x 3" detector and thus the
corresponding angular correction factors were much smaller.
The angular corrections for other energies and other source
distributions were estimated on the basis of these two
calculations.
Due to the flatness of the angular response
the errors involved in these estimates are negligible.
(¢/I), the ratio of primary flux to total dose rate, is
the same as given in HASL-150 except for the case of the
1.76 Mev 214Bi photopeak used for the dose rate estimate of
the 238U series.
This particular ratio was revised slightly
based on further analysis of existing 214Bi decay schemes
and y-ray intensity measurements.
The final field spectra conversion factors (Np/I),
absorption peak counts per ur/hr, are given in Tables II
and III.
These values were verified by direct field
comparison with the 5" x 3" detector at a large number of
locations.
The values of (Np/I) for the three natural
emitters, 40x, the 238y series, and the 232TH series, are
significantly higher than the corresponding values for the
5" x 3" NaI(Tl) detector.
Thus,
estimates of peak areas
should be affected less by errors in estimating the continuum
resulting in more precise dose rate estimates.
The
(Np/I)
for the various fallout emitters are also slightly higher.
This increase in response is due primarily to the improved
geometrical configuration, which results in a larger
intrinsic peak efficiency for higher energy y-rays and an
improved angular response at all energies.
In addition, the
improved resolution allows a better estimate of the 1.76 MeV
214Bi absorption peak, even in the presence of a large 1.46
MeV 40K peak.
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