THE EGS5 CODE SYSTEM

Table 2.4: Materials used in reference tables of scattering strength vs. characteristic dimension at
various energies.
Material Z Z(Z + 1) A ρ Z(Z + 1)/A
Li 3 12 6.93900 0.5340 1.7294
C 6 42 12.01115 2.2600 3.4968
H 2 O 10 76 18.01534 1.0000 4.2186
Al 13 182 26.98150 2.7020 6.7454
S 16 272 32.06435 2.0700 8.4829
Ti 22 506 47.90000 4.5400 10.5637
Cu 29 870 63.54000 8.9333 13.6922
Ge 32 1056 72.59000 5.3600 14.5475
Zr 40 1640 91.22000 6.4000 17.9785
Ag 47 2256 107.87000 10.5000 20.9141
La 57 3306 138.91000 6.1500 23.7996
Gd 64 4160 157.25000 7.8700 26.4547
Hf 72 5256 178.49000 11.4000 29.4470
W 74 5550 183.85000 19.3000 30.1877
Au 79 6320 196.98700 19.3000 32.0833
U 92 8556 232.03600 18.9000 36.8736
To generate the data sets, then, for each of the 16 reference materials, 45 reference energies,
and 29 broomstick lengths and diameters (i.e., characteristic dimension) a series of Monte Carlo
simulations were performed, using up to 25 different values of fractional energy loss (called EFRACH
in EGS5), covering the range from 30% to 0.001% (except when such steps were less than the
theoretical lower limits of the Molière distribution). Energy loss hinges were set to the lesser of
EFRACH and 4% fractional energy loss, and 100,000 histories were simulated, resulting in relative
statistical uncertainties in the computed values of 〈r〉 at 2σ of around 0.3%. Tallies were made of
the the average track length inside the volume, the average lateral displacement of the particles
escaping the end of the volume, the average longitudinal displacement of particles escaping the
sides of the broomstick, and the fractional energy deposited, backscattered and escaping from the
side of the broomstick. Computations of the number of hinges expected for the scattering strength
being tested given the broomstick dimension, were also made for each run, and the anticipated
number of collisions per hinge were also determined and stored.
Illustrative plots showing the divergence in the results as step-sizes are increased in Copper
at 5 MeV for several different broomstick thicknesses are shown in Figures 2.17 (results of energy
deposition) and 2.18 (results of lateral spread).
Approximately 20,000 such plots were generated from over 500,000 simulations to encompass the
desired ranges of materials, energies, and characteristic dimensions. The data was then analyzed
to determine the maximum fractional energy loss which showed convergence within the statistical
uncertainty of the data, using a least-squares fit to a line with slope zero and intercept given by the
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