PENELOPE 2003 - OECD Nuclear Energy Agency

192 Chapter 6. Structure and operation of the code system
(iii) Angular distributions of transmitted and backscattered particles.
(iv) Depth-dose distribution (i.e. deposited energy per unit depth).
(v) Depth-distribution of deposited charge.
(vi) Distribution of energy deposited into the slab.
Each simulated continuous distribution is printed on a separate file (as a histogram),
with a heading describing its content and in a format ready for visualization with a
plotting program. The code computes and delivers the statistical uncertainties (3σ) of
all evaluated quantities and distributions. Many authors quote these uncertainties as
one standard deviation, which means that the probability for the actual value to lie
outside the error bar is 0.317. We prefer to be more conservative and stay at the 3σ
level, for which the probability of “missing the real value” is only 0.003.
The program PENSLAB and its predecessors have been intensively used during the
last years to analyze the reliability of penelope. They have been applied to a variety
of experimental situations, covering a wide energy range. Benchmark comparisons with
experimental data have been published elsewhere (Baró et al., 1995; Sempau et al.,
1997).
WARNING: In the output files of PENSLAB (and also in those of the program PENCYL
described below), the terms “transmitted” and “backscattered” are used to denote particles
that leave the material system moving upwards (W > 0) and downwards (W < 0),
respectively. Notice that this agrees with the usual meaning of these terms only when
primary particles impinge on the system coming from below (i.e. with W > 0).
6.2.2 Program PENCYL
The program PENCYL simulates electron and photon transport in multilayered cylindrical
structures. The material system consists of one or several layers of given thicknesses.
Each layer contains a number of concentric homogeneous rings of given compositions and
radii (and thickness equal to that of the layer). The layers are perpendicular to the z-axis
and the centre of the rings in each layer is specified by giving its x and y coordinates.
When all the centres are on the z-axis, the geometrical structure is symmetrical under
rotations about the z-axis (see fig. 6.3).
Primary particles of a given kind, KPARP, are emitted from the active volume of
the source, either with fixed energy SE0 or with a specified (histogram-like) energy
spectrum. The initial direction of the primary particles is sampled uniformly inside a
cone of (semi-) aperture SALPHA and with central axis in the direction (STHETA, SPHI).
Thus, SALPHA = 0 defines a monodirectional source and SALPHA = 180 deg corresponds
to an isotropic source.
The program can simulate two different types of sources:
a) An external point or extense (cylindrical) homogeneous source, defined separately
from the geometry of the material system, with its centre at the point (SX0, SY0, SZ0).