GEANT321/gstrag/gstren.F

   1 *
   2 * $Id$
   3 *
   4 * $Log$
   5 * Revision 1.1.1.1  1995/10/24 10:21:39  cernlib
   6 * Geant
   7 *
   8 *
   9 #include "geant321/pilot.h"
  10 *CMZ :  3.21/02 29/03/94  15.41.25  by  S.Giani
  11 *-- Author :
  12       FUNCTION GSTREN (GAMMA,ECUT,STEP)
  13 C.    ******************************************************************
  14 C.    *                                                                *
  15 C.    *   Simulation of energy loss straggling in thin layers.         *
  16 C.    *   Sampling is done from the tables which are prepared          *
  17 C.    *   in GSTINI.                                                   *
  18 C.    *                                                                *
  19 C.    *   ==> Called by : GTELEC, GTHADR, GTMUON                       *
  20 C.    *       Authors   : K. Lassila-Perini, I. Gavrilenko             *
  21 C.    *                                                                *
  22 C.    ******************************************************************
  23 #include "geant321/gcbank.inc"
  24 #include "geant321/gcjloc.inc"
  25 #include "geant321/gcmate.inc"
  26 #include "geant321/gcstra.inc"
  27 C
  28       DIMENSION ANGL(200),RNDM(2)
  29 C...
  30 *   Reading the tables, if the medium has not changed
  31       NP     = Q(JTSTRA+1)
  32 *
  33       EC       = 1.E9*ECUT
  34       GSTLOC   = 0.
  35       IF(STEP.LE.0.) GO TO 90
  36 C...
  37 *   Interpolate the tables for the current gamma-factor
  38       GAML     = LOG(GAMMA)
  39       IF(GAML.GT.GAMLOG(21)) THEN
  40          DO 10 J=1,NP
  41             ANGL(J)=Q(JTSTCO+J*21)
  42    10    CONTINUE
  43       ELSE
  44 C...
  45          DO 20 I = 2,21
  46             IF(GAML.LE.GAMLOG(I)) THEN
  47                DGG = (GAML-GAMLOG(I-1))/(GAMLOG(I)-GAMLOG(I-1))
  48                IP=I
  49                GO TO 30
  50             ENDIF
  51    20    CONTINUE
  52    30    DG1=1.-DGG
  53 C...
  54          DO 40 K = 1,NP
  55             ANGL(K) = Q(JTSTCO+(K-1)*21+IP-1)*DG1+
  56      +                Q(JTSTCO+(K-1)*21+IP  )*DGG
  57    40    CONTINUE
  58       ENDIF
  59 *
  60 *    The sampling from the tables
  61       ANMIN   = EXP(ANGL(NP))
  62       ANMAX   = EXP(ANGL( 1))
  63 *
  64       DAN      = ANMAX-ANMIN
  65       AMU      = DAN*STEP
  66       CALL GPOISS(AMU,N,1)
  67       NICOLL   = MAX(N,1)
  68       DO 80  I  = 1,NICOLL
  69    50    K1 = 1
  70          K2 = NP
  71          CALL GRNDM(RNDM,1)
  72          R = LOG(RNDM(1)*DAN+ANMIN)
  73    60    K = (K1+K2)/2
  74          IF(R.GT.ANGL(K)) THEN
  75             K2=K
  76          ELSEIF(R.LT.ANGL(K)) THEN
  77             K1=K
  78          ELSE
  79             E=Q(JTSTEN+K)
  80             GOTO 70
  81          ENDIF
  82          IF(K2-K1.GT.1 ) GO TO 60
  83 *
  84          E = Q(JTSTEN+K2)+(R-ANGL(K2))*
  85      +       (Q(JTSTEN+K1)-Q(JTSTEN+K2))/(ANGL(K1)-ANGL(K2))
  86    70    EE = EXP(E)
  87          IF(EE.GT.EC) GO TO 50
  88 *
  89 * *** Total energy calculation
  90          GSTLOC = GSTLOC+EE
  91    80 CONTINUE
  92 *
  93    90 GSTREN  = GSTLOC*1.E-9
  94       END