7 about 18%
ithe calculation cannot be relied upon other than as a check
conditions
rate is from
> in the
in most
on a careful
>ffects,
jiation
an
3 reduced
The
The value of the
ff; onization current per ur/hr for gamma rays obtained by
Fcalculation was 4.45 x 10714 amperes.
This calculation is
given in detail in Appendix 1.
reareful
determined
ypted to
ha-rays
experimental calibration.
lwas
calibration using
an NBS
The value obtained from a
standardized radium source
(4.60 + .10) x 10714 amperes/ur/hr.
The latter value
lwas also obtained (to within 2%) using less accurately
i standardized 60¢59 and 137cs sources.
The calibration
iprocedure adequately accounts for the effect of scattered
igamma-rays from the laboratory floors and ceiling by careful
Fshadow shielding of the source.
Both of the above calibration
‘factors are for 59 atmospheres of gas and normal incidence
fof gamma rays to the chamber axis.
|
The calculation of ionization current per ur/hr for cosmic
3 pressure
‘radiation
ost due to
co gas
ȣ electrons
ss than 1%
ionization produced inal atm. argon filling to that which
‘would be produced in 1 atm. of air, but this time the incident
fparticles are primarily high energy electrons and muons rather
than gamma-rays.
In the gamma ray case the ratio of ionization
1own to
to gamma
again requires
the determination of the relative
produced in argon relative to air depends primarily on the
irelative Compton cross sections for the two media while in
ithe cosmic ray case this ratio depends on the relative values
of the mass energy stopping powers
1 calculations electronic particles.**’
7eé contamjligible
1i1t dose
for minimum ionizing
These ratios are not necessarily
the same although they do turn out to be guite similar.
The
theoretical stopping power prediction for the number of ion
pairs produced in
argon to that
in
air per unit
flux is
about
'1.51,797°
However, measurements of this quantity made by
Several investigators under thick shields sufficient to shield
ays can be
Out all particles except muons predict a value of about
juires an
ses and the
effects of the wall, we calculate a cosmic ray calibration
factor of 5.01 x 10714 amperes/ (ur/hr).
(See Appendix 1)
jamma rays
the wall
suring the
rlinders of
From our independently derived cosmic ray ionization curve
VS. pressure altitude and calculated values of the total
ionization intensity at sea level® we deduce a value of
,5.09 x 10714 amperes/ur/hr.
The latter value is used
lis calculaynization
tonsidering
; as well
ig pressure,
peg ge wn
[1.69,2¥22*3
(corrections
If we use the latter value along with slight
for the attenuating and electron enhancement
froutinely.
The agreement of the two calibration factors given above
‘Suggests a significant discrepancy between the experimental
-
~o
3f