and theoretical ratios of ionization for fast charged particles
in argon relative to air which may be partly responsible for
the higher values of cosmic-ray ionization in the lower
5
atmosphere measured by Neher using argon filled chambers.
In order to pursue this question further we are planning with
the cooperation of the NYU group to expose two identical thin
walled chambers filled with argon and air, respectively, to the
predominantly cosmic ray field on a large lake.
If both
chambers are properly saturated the resultant ratio of ion
currents per atmosphere should be helpful in investigating
this discrepancy.
If the experimental value of 1.65 - 1.70
is verified then further study will be necessary to explain
why present stopping power theory fails to predict this value.
Since the experimental value of 1.65 was obtained in all
cases using thick walls it is possible that the discrepancy
may be related to a fast particle wall effect, although
Johnston’? claims this is unlikely.
It is clear, however,
that the interaction of high energy particles with a thick-
walled chamber is still not perfectly understood and is worthy
of continued study since such chambers are still being used
on balloon flights for high altitude cosmic ray studies.’ *
Theoretical Investigation of Gamma Ray Transport
Our present theoretical calculations of dose rates for
various source distributions in the soil and air, based on
the dose rate buildup theory of O'Brien et al,** is apparently
adeguate for the calculation of the total dose rate from
distributed sources.
However, it does not allow a calculation
of the angular distribution or energy spectrum of the incident
flux at the detector.
The knowledge of these distributions
would be valuable in interpreting the response of various
types of instrumentation to different kinds of source
distributions and source energies as well as for calculating
the actual energy deposition in various organs of the body.
At present these distributions can be calculated only by time
consuming Monte Carlo methods.
Because of the machine time
required these methods have only been applied to a few
particular problems and only for a few source energies.
In
particular Monte Carlo calculations have substantiated the
experimental prediction of an interface effect for a point
source near the boundary of two media of very different