CERN Program Library Long Writeup W5013 - CERNLIB ...

Counts
900
800
Landau
700
40
600
20
500
400
10
300
1
5
200
0.5
100
0
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
dE/dx [GeV/cm] x ‘ 10 -4
Figure 38: Energy loss distribution for a 3 GeV electron in Argon as given by standard GEANT. The width of
the layers is given in centimeters.
It is assumed that the atoms have only two energy levels with binding energy E 1 and E 2 . The particle–
atom interaction will then be an excitation with energy loss E 1 or E 2 , or an ionisation with an energy loss
distributed according to a function g(E) ∼ 1/E 2 :
g(E) = (E max + I)I
E max
1
E 2 (1)
The macroscopic cross-section for excitations (i =1, 2) is
Σ i = C f i ln(2mβ 2 γ 2 /E i ) − β 2
E i ln(2mβ 2 γ 2 (1 − r) (2)
/I) − β2 and the macroscopic cross-section for ionisation is
Σ 3 = C
E max
I(E max + I)ln( Emax+I
I
) r (3)
E max is the GEANT cut for δ-production, or the maximum energy transfer minus mean ionisation energy, if
it is smaller than this cut-off value. The following notation is used:
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