ORNL-1771 - Oak Ridge National Laboratory

11. SHIELDING ANALYSIS
J. E. Faulkner
H. E. Hungerford
Theoretical analyses have been made so that an
understanding of the air and ground scattering
measurements at the Tower Shielding Facility could
be obtained and the attenuation in the side wall of
an aircraft crew shield could be determined. In
connection with the air and ground scattering analy-
ses, special attention was given to the calculation
of the reduction of air scattering due to ground
interruption and to the effects of multiple scattering.
The gamma-ray slant penetration has been calcu-
lated for the side wall of an aircraft crew shield,
and the variation of radiation intensity throughout
the crew volume has been briefly explored.
SLANT PENETRATION OF COMPOSITE
SLAB SHIELDS BY GAMMA RAYS
C. D. Zerby
The total radiation dose in the crew compartment
of an airplane is partially dependent on the gamma-
ray flux penetrating the compartment shield. To
obtain a fundamental, but practical, knowledge of
the gamma-ray penetrations, the problem has been
treated theoretically by using stochastic, or Monte
Carlo methods.
The problem was programed for solution on the
ORACLE and was arranged for investigating the
effects of the variations of all the parameters in-
volved. The shield was taken as a composite slab
of two materials comprising a thick layer of Compton
scattering material' followed by a thin layer of
lead. In each of many cases the initial incident
photons were taken as monoenergetic and incident
on the slab at a particular angle with the normal to
the slab. The stochastic process used the exacf
physical analog of the probability laws known to
govern the life of a photon.
'In the range of energy considered, the Compton
scatterer has approximately the same physical charoc-
terlstics relative to a photon passing through it as does
coricrete or polyethylene (CH2).
E. P. Blizard
F. H. Murray
C. D. Zerby
Physics Division
H. E. Stern
Consolidated Vu1 tee Aircraft Corporation
The parameters and their variations that have
been investigated to date are listed below:
Thickness of Compton
Thickness of lead, in.
in. 3, 9, 15
bo, 3/10, Y2
3
Initio1 photon energy, mc2 units 2, 6
Initial angle of incidence, deg
0, 30, 60
All combinations of these parameters were investi-
gated.
The following solution of a typical problem indi-
cates part of the information obtained:
Initial Conditions
Results
Thickness of Compton scatterer 3 in.
Thickness of lead
Initial photon energy
>,o in.
6 mc 2
Initial angle of incidence 60 deg
Fraction of initial energy
1. reflected 0.0234
2. absorbed in the Compton scatterer owing
to scattering collisions
0.318
3. absorbed in lead owing to scattering
collisions
0.0568
4. absorbed In lead awing to absorption
cat I is ions
0.0515
5. penetrating shield 0.550
6. penetrating shield without being
degraded in energy
0.435
Energy build-up factor 1.265
The energy spectrum for the reflected photons
was also obtained in this typical problem. The
spectra for the photons penetrating the shield were
obtained in the angle intervals 0 to 15, 15 to 30,
30 to 45, 45 to 60, and 60 to 90 deg. These spectra
will be available in a forthcoming report.
_____ ...... .............
2The electron density of the Compton scatterer was
taken as the same as that for polyethylene.
3Multiply mc 2 units by 0.5108 to obtain MeV.
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