igh pressure Ionization Chambers
dad the 238y
(78 Mev
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nstant
ly a few
y following
ts
matural and fallout y-radiation requires very sensitive
Hnstrumentation capable of providing precise readings under
The instruments we have
11 kinds of field conditions.
jJeveloped for measuring these total gamma dose rates are
eeveral steel-walled cylindrical ionization chambers filled
e
to high pressures with the purest commercially available
ion-
ing the
was
our recent
however,
The measurement of the very low ionization levels from
argon.
Our newest model is shown in Figure 4.
This chamber*
in
1/2"
6
and
long
12"
tank
cylindrical
a
of
onsists
Jiameter with a .135"thick stainless steel wall.
i$ probably
|
Its sensitive volume of 5.58 liters was originally filled
mall increaseto a pressure of 1000 psi with argon.
The ionization current
accounted
s measured by a Victoreen Dynamic Capacitor Electrometer to
the NYU
mn accuracy of about 1% (after careful calibration of
electrometer output voltage reading with a potentiometer).
lon from
oil
A precision of 1-2% can also be obtained by averaging a
iental
hard to
lecessitate
ied from a
- reduced
‘rn and
2 and 1963
ig
spot
men a
xn over a
the
arge number of instantaneous readings taken in rapid
The chamber is equipped with a switch to allow
parse numb
the potential between the wall and guard ring to be reversed.
easurements are always made for both polarities to cancel
ny small unidirectional polarization currents which are
ometimes induced in the insulators.
The chamber has been
ound to be saturated for gamma fields in excess of 100
r/hr when used at an operating potential of 300 V.
The
00 V battery is located in an aluminum can on top of the
pressure vessel along with the head of the electrometer.
he electrometer readout unit can be operated up to 150 ft.
way through
a cable connection,
thus
eliminating shielding
of the chamber by the operator.
The energy response of this chamber was investigated
tre carefully6905 £920 Kev using a filtered X-ray beam as well as
TF
Cs and
Ce gamma sources.
Although the
ition prove
ons in the
din
attenuating effect of the steel wall becomes very large for
Ow energy gamma rays,
these experiments substantiated our
heoretical predictions that this effect would be significantly
oderated by the increased absorption of low energy gamma
ays in argon relative to air.
"RSG-42
The net reduction in dose
Ionization Chamber manufactured to our specifications
PY Reuter-Stokes,
Inc., Cleveland, Ohio.
- 23 -
Pee aye
226Ra,
-
~
.