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