GEANT321/gphys/gcompi.F

   1 *
   2 * $Id$
   3 *
   4 * $Log$
   5 * Revision 1.1.1.1  1995/10/24 10:21:23  cernlib
   6 * Geant
   7 *
   8 *
   9 #include "geant321/pilot.h"
  10 *CMZ :  3.21/02 29/03/94  15.41.21  by  S.Giani
  11 *-- Author :
  12       SUBROUTINE GCOMPI
  13 C.
  14 C.    ******************************************************************
  15 C.    *                                                                *
  16 C.    *  Calculates cross-section in current material                  *
  17 C.    *  for COMPTON scattering.                                       *
  18 C.    *                                                                *
  19 C.    *  The total cross-section of L.Urban is used to estimate the    *
  20 C.    *  photon mean free path.                                        *
  21 C.    *    It gives a good description of the data from 10KeV to       *
  22 C.    *    100/Z GeV                                                   *
  23 C.    *                                                                *
  24 C.    *    ==>Called by : GPHYSI                                       *
  25 C.    *       Authors    R.Brun, L.Urban  *********                    *
  26 C.    *                                                                *
  27 C.    ******************************************************************
  28 C.
  29 #include "geant321/gcbank.inc"
  30 #include "geant321/gctrak.inc"
  31 #include "geant321/gconsp.inc"
  32 #include "geant321/gcmate.inc"
  33 #include "geant321/gcjloc.inc"
  34 #include "geant321/gcmulo.inc"
  35       DIMENSION PCOMP(12),P(4)
  36       DATA AC,BC,CC/20.,230.,440./
  37       DATA PCOMP/ 0.27965,-0.18300,0.67527E+1,-0.19798E+2,
  38      +            0.19756E-4,-0.10205E-1,-0.73913E-1,0.27079E-1,
  39      +           -0.39178E-6,0.68241E-4,0.60480E-4,0.30274E-3/
  40       DATA PI2R2I/2.004275/
  41 C.
  42 C.    ------------------------------------------------------------------
  43 C.
  44 C             Energy cut-off above which we ignore COMPTON scattering.
  45 C
  46       SIG=0.
  47       IF(Z.LT.1.)GO TO 90
  48       EGAM   = ELOW(IEKBIN)
  49       X=EGAM/EMASS
  50       IF(EGAM.GT.(100./Z))GO TO 90
  51       X2=X*X
  52       JPROB=LQ(JMA-4)
  53 C
  54       DO 20 I=1,4
  55          C=1.
  56          P(I)=0.
  57          DO 10 J=1,3
  58             JJ=4*J+I-4
  59             P(I)=P(I)+C*PCOMP(JJ)
  60             C=C*Z
  61   10     CONTINUE
  62   20  CONTINUE
  63 C
  64       SIG=P(1)*LOG(1.+2.*X)/X
  65       SIG=SIG+(P(2)+P(3)*X+P(4)*X2)/(1.+AC*X+BC*X2+CC*X2*X)
  66       SIG=PI2R2I*Q(JPROB+17)*SIG
  67 C
  68   90  IF(SIG.GT.0.)THEN
  69          Q(JCOMP+IEKBIN)=1./SIG
  70       ELSE
  71          Q(JCOMP+IEKBIN)=BIG
  72       ENDIF
  73 C
  74       END