THE EGS5 CODE SYSTEM

The main purpose of this section, however, is to demonstrate how to incorporate importance
sampling into an EGS5 problem, so we will not discuss the geometry techniques any further. Instead,
those interested in the cylinder-slab generalization are referred to the commented FORTRAN
listing of UCCYL.
4.1.2 Particle Splitting
A version of UCCYL was used to answer a number of questions about energy deposition in a
positron production target, as well as regions surrounding such a target. Two of these questions
are: what is the temperature rise in the target and what is the radiation damage to nearby vacuum
O-rings, when 10 13 electrons/sec with energies of 33 GeV strike the target?
One of the first things observed during initial EGS runs was that the statistics in the (backward)
region designated as an “O-ring” were quite low because
1. the region of interest was too small,
2. the majority of the shower was forward-directed and only low energy radiation headed backwards
towards the region, and
3. there was too much shielding material separating the the region of interest from the source.
However, by studying the energy deposition block diagrams (from auxiliary routine ECNSV1) and
the associated event counters (from NTALLY), obtained during the initial computer runs, we were
able to make the following observations and recommendations:
• Most of the charged particles depositing energy come from photons interacting in the region
of interest–not from charged particles entering from surrounding regions (ı.e. the “cavity” is
fairly big).
• The region (“cavity”) is small enough, however, that only a fraction of the photons traversing
the region interact (verified by simple calculation).
• Suggestion: Every time a photon first enters the region, split it into 10 identical photons,
1
each carrying a weight of
10
to the progeny; include the weight in the EDEP (and any other)
scoring.
This was accomplished by placing the following statement in HOWFAR:
if (irsplt(irl).eq.1.and.irl.ne.irold.and.iq(np).eq.0) then
! Apply particle splitting
if (lsplt.ne.0) then
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