THE EGS5 CODE SYSTEM

necessary geometry input. The following data, which is in the familiar MORSE-CG format [168]
and which is included as file ucsampcg.data of the EGS5 distribution, is used by UCSAMPCG
to model with CG the same geometry treated by UCSAMPL5 in a non-CG implementation.
RPP 1 -1.5 1.5 -1.5 1.5 0.0
3.0
RPP 2 -2.5 2.5 -2.5 2.5 -1.0
4.0
END
Z1 +1
Z2 +2 -1
END
1 0
The HOWFAR routine supplied with UCSAMPCG is general and can be used for any CG geometry
which can be specified by the five types of bodies listed above. All that is required of the user is
the creation of an appropriately formatted input data file. It must be noted, though, that because
of the computational overhead introduced in generalizing HOWFAR, for problems involving simple,
regular geometries (such as cylindrical slabs or rectangular pixels), EGS5 user codes using CG will
execute 1-2 times more slowly than user codes tailored to the particular problem geometries. (This
is a substantial improvement relative to the CG implementation in EGS4, which was “significantly
less efficient than the macro-geometry methods” [171].) For many problems, the greatly facilitated
ease in setting up the simulation geometry with CG will more than offset the slight penalty in
computational efficiency.
To facilitate the construction of CG geometry input files and to provide for the display of particle
trajectories from EGS5 simulations, Namito and co-workers [123] developed a stand-alone visual
interface program, cgview, which is freely distributed on the Internet at:
http://rcwww.kek.jp/research/egs/kek/cgview/.
The geometry used in UCSAMPCG and some sample output particle trajectories drawn with
cgview are shown in Fig. 4.5.
Cgview can also be used to assist in the construction of CG input data files. For geometries
with simple shapes, users can select and position volume elements visually using tools provided
with cgview, and later have the program create output data files in the correct MORSE-CG format.
Additionally, the integrity of existing CG input data files can be checked through the use of the
cgview pseudo particle feature. This function allows the user to specify locations and directions for
pseudo source particles, which are then tracked by cgview through the input geometry, searching
for regions of overlapping and undefined zones. Thus, errors in geometry specification may be
corrected prior to being used in Monte Carlo simulations.
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