THE EGS5 CODE SYSTEM

IBRSPL and NBRSPL The parameters IBRSPL and NBRSPL allow the user to improve the efficiencies
of simulations in which low-probability bremsstrahlung photon production is important by splitting
the secondary particles. The method is similar to that described above for splitting in x-ray
production following electron-impact ionization. When the parameter IBRSPL, which has a default
value of 0 and is found in COMMON BREMPR, is set to 1, each electron bremsstrahlung event will result
in the generation of NBRSPL appropriately weighted photons.
CEXPTR The parameter CEXPTR, found in COMMON USERVR, is a scaling factor which can be used
to either force or inhibit photon collisions in regions with cross section that are very small or very
large. If λ is the photon mean free path and we use C to represent the scaling factor CEXPTR, we
have for the interaction probability distribution:
˜p(λ)dλ = (1 − Cµ)e −λ(1−Cµ) dλ,
where the overall multiplier 1 − Cµ is introduced to ensure that the probability is correctly normalized,
i.e. ∫ ∞
0
˜p(λ)dλ = 1. For C = 0, we have the unbiased probability distribution e −λ dλ. One sees
that for 0 < C < 1, the average distance to an interaction is stretched and for C < 0, the average
distance to the next interaction is shortened. Note that the average number of mean free paths to
an interaction, 〈λ〉, is given by 〈λ〉 = ∫ ∞
0
λ˜p(λ)dλ = 1
1−Cµ .
NOMSCT The user may override all treatment of electron multiple-scattering in a given region by
setting the switch NOMSCT(MXREG) to be 1 for that region. NOMSCT which is a part of COMMON MISC
and is initialized 0, is used primarily as a debugging and code development tool, and is included in
this description for completeness only.
Random number generator initialization
Whenever EGS (including any part of the user code) requires a floating point random number taken
uniformly from the interval (0,1) to be returned to a variable (all EGS5 routines use the variable
name RNNOW), the following statement is required:
call randomset(rnnow)
EGS5 employs the random number generator RANLUX, implemented by James. Depending on
the input specification, called the “luxury level,” RANLUX provides random sequences which pass
different levels of tests for randomness and execute at different speeds. Independent random sequences
for the same luxury level can be generated with RANLUX by simply specifying a different
input “seed,” any integer in the range from 1 to 2 31 . The default luxury level, as defined in the variable
LUXLEV of COMMON RLUXDAT in file include/randomm.f, is 1, and the default seed, INSEED,
is 314159265. RANLUX is initialized by HATCH using the defaults for LUXLEV and INSEED unless the
user specifies different values prior to the HATCH call. In addition, users may initialize the generator
themselves at any time by invoking
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