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[u/mrichter/AliRoot.git] / GEANT321 / gphys / gprsgg.F
1 *
2 * $Id$
3 *
4 * $Log$
5 * Revision 1.1.1.1  1995/10/24 10:21:33  cernlib
6 * Geant
7 *
8 *
9 #include "geant321/pilot.h"
10 *CMZ :  3.21/04 24/02/95  14.49.53  by  S.Giani
11 *-- Author :
12       FUNCTION GPRSGG(Z,E)
13 C.
14 C.    ******************************************************************
15 C.    *                                                                *
16 C.    *  To calculate cross-section for e+e- production                *
17 C.    *  by photons (in barn/atom)                                     *
18 C.    *                                                                *
19 C.    *    ==>Called by : GPRSGA                                       *
20 C.    *       Author    L.Urban  *********                             *
21 C.    *       Modified by: G.Battistoni                                *
22 C.    *                                                                *
23 C.    *   constant cross section is assumed above 100 GeV !            *
24 C.    ******************************************************************
25 C.
26 #include "geant321/gconsp.inc"
27       DIMENSION C(18),CC(3)
28       DATA C/ 0.87842E-3,-0.19625E-2, 0.12949E-2,-0.20028E-3
29      +      , 0.12575E-4,-0.28333E-6,-0.10342E-4, 0.17692E-4
30      +      ,-0.82391E-5, 0.13063E-5,-0.90815E-7, 0.23586E-8
31      +      ,-0.45263E-3, 0.11161E-2,-0.86749E-3, 0.21773E-3
32      +      ,-0.20467E-4, 0.65372E-6/
33       DATA EUPP/100./
34 C.
35 C.    ------------------------------------------------------------------
36 C.
37       SIG=0.
38 *
39       ESAV=E
40       IF(E.GT.EUPP) E=EUPP
41 *
42       IF(E.LE.2.*EMASS)GO TO 90
43       X=LOG(E/EMASS)
44       DO 20 I=1,3
45          CC(I)=0.
46          D=1.
47          DO 10 J=1,6
48             JJ=6*I+J-6
49             CC(I)=CC(I)+D*C(JJ)
50             D=D*X
51   10     CONTINUE
52   20  CONTINUE
53 C
54       SIG=Z*(Z+1.)*(CC(1)+CC(2)*Z+CC(3)/Z)
55 C
56   90  IF(SIG.LT.0.)SIG=0.
57       GPRSGG=SIG
58 *
59       E=ESAV
60 *
61       END