a
ionization at one meter above the ground were 7I(ion pairs/
JIES
cm3/sec at 760 mm. and 0°C) due to gamma rays and cosmic
rays and about 131 due to beta rays.
We have attempted to calculate, using the theoretical
approach of O'Brien etal*® the free air B-ray ionization
expected from the major beta emitters in the soil.
Their
results suggest that one group transport theory can be
successfully applied to environmental beta ray dosimetry.
Using estimates from deposition data of 90sr, 144¢ce and
all
Lout
»le
se of
LO6Rh present in the soil at the time of the Greenwood Lake
1 to
measurements and our spectrometric estimates of 40x, 238y,
and 232Th concentrations at the site, we calculated the
total B-ray ionization expected at various heights.
The
calculation, however, is extremely sensitive to the depth
distribution of beta emitters in the soil, much more so
it mis3.
The
len
zation
recuced
sucth
as
and
sarried
1e gamma
ined by
ober
vith
an
num wall
xf heights
amma plus
rant
over
id the
Llog paper
ing points
a halfras
than for gamma emitters.
The theory does predict an
approximately exponential decrease with height; however the
calculated absolute ionization intensities are significantly
less than the values inferred from the chamber measurements.
If we consider only fallout emitters the calculation of half
~ thickness in air is less dependent on depth distribution or
A half thickness of ~150 mg/cm? is then
source intensity.
- verified by the theory.
The discrepancy in absolute
lonization intensity could well be due to errors in assumed
Be
asure
sur
7S.
pi ARES + oe ee es
$O cm to
3
about
the
al f-
source intensity and/or distribution or to an incorrect
1onization chamber wall correction.
Measurements at other
* Sites with other instruments are clearly necessary before
any final conclusions can be made as to the agreement of
' experiment and theory.
Further experimental studies using new ultra thin-walled
ionization chambers
constructed of different materials
as
} well as sets of filters which can be placed over the chambers
| are planned in conjunction with the NYU group.
A more intense
theoretical study, combined with the results of these planned
experiments, should provide a reasonable picture of the
contribution of B-rays to the external environmental
radiation
field.
> times
In any case, these weakly penetrating f-rays contribute
> size
proximation / Only a very small fraction of the total dose received by the
‘ Gonads or bone marrow.
air