THE EGS5 CODE SYSTEM

Figure 4.4: UCBEND simulation at 8.5 MeV (B=0 kG).
programs have been developed to assist in the construction of problem geometries by defining
regions to be the unions and/or intersections of sets of basic volume elements of varying sizes. In
Monte Carlo applications, this method for creating geometries through the combining of smaller
volumes has come to be referred to as “combinatorial geometry,”, or CG. Note that this usage is not
exact, as the term combinatorial geometry actually denotes a much more extensive mathematical
field (see, for example, the book by Pach and Agarwal[129]).
In this section we describe the advanced EGS5 user code UCSAMPCG, which exploits the
features of combinatorial geometry. The CG package invoked by UCSAMPCG is included in the
EGS5 distribution in the auxiliary source code file cg_related.f, and is based on the well-known
MORSE-CG[168] combinatorial geometry Monte Carlo program. The MORSE-CG package was
originally adapted to EGS4-PRESTA by Torii and Sugita [171], and Sugita and Torii have further
modified it for EGS5 [169]. The subprograms of cg_related.f have retained the MORSE-CG
methodology for constructing and evaluating geometry, and the EGS5 implementation is compatible
with MORSE-CG input files. Five elemental volume shapes can be modeled: rectangular
parallelepipeds (RPP), spheres (SPH), right circular cylinders (RCC), truncated right angle cones
(TRC), and tori (TOR). As mentioned above, more complicated volumes can be specified by appropriately
intersecting these five basic bodies. The reader is referred to the MORSE-CG manual [168]
and the Torii and Sugita citations [171, 169] for detailed descriptions of the CG adaptation and
implementation, as well as for instructions on creating input files.
User code UCSAMPCG uses combinatorial geometry to simulate the same problem which the
sample user code UCSAMPL5, presented in great detail in the EGS5 User Manual (see Appendix B
of this report), treats with a simple geometry model. The coupling of the CG package to EGS5 is
accomplished entirely within subroutine HOWFAR, which performs the actual boundary and region
checks. A once-only initialization is done by calling the CG routine GEOMGT, which reads in the
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