CERN Program Library Long Writeup W5013 - CERNLIB ...

Geant 3.16 GEANT User’s Guide CONS110
Origin : R.Brun, M.Maire, J.Allison Submitted: 01.06.83
Revision : Revised: 08.12.93
Documentation : M.Maire
Mixtures and Compounds
CALL GSMIXT
(IMATE,NAMATE,A,Z,DENS,NLMAT,WMAT*)
Defines mixture or compound IMATE as composed by NLMAT materials defined via the arrays A, Z and WMAT.
Mixtures of compounds can also be defined.
IMATE (INTEGER) user material (mixture) number;
NAMATE (CHARACTER*20) mixture name;
A
(REAL) array of atomic weights;
Z
(REAL) array of atomic numbers;
DENS (REAL) density in g cm −3 ;
NLMAT (INTEGER) number of elements in the mixture;
> 0 WMAT contains the proportion by weights of each material in the mixture;
< 0 WMAT contains the proportion by number of atoms of each kind, the content of WMAT
in output is changed to contain the relative weights;
Method
For a compound (NLMAT < 0), the molecular weight and charge are:
A mol = ∑ i
n i A i
Z mol = ∑ i
n i Z i
where n i = WMAT(I) is the number of atoms of the i th component of the molecule. In this case the proportion
by weight is:
p i = n iA i
A mol
where p i = WMAT(I) in output. From the relative weights, GSMIXT works out the effective atomic weight
and atomic number according to the following formulas:
A eff = ∑ i
p i A i
Z eff = ∑ i
p i Z i
which are stored in the JMATE data structure [CONS199] together with the radiation length.
The radiation length is computed according to the EGS manual [12], formula 268 (37), for an element:
[
1
=4αr0 2 ρX N 1
Av
0 A Z(Z + ξ(Z)) ln 183 ]
Z 1/3 − F c(Z)
where
X 0 radiation length (in cm);
ρ density (in g cm −3 );
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