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ADAS Subroutine qbchid

       FUNCTION QBCHID(Z,XI,ZETA,ENER)
       IMPLICIT REAL*8(A-H,O-Z)
C-----------------------------------------------------------------------
C
C  ********************* FORTRAN77 SUBROUTINE QBCHID *******************
C
C  PURPOSE:
C   EVALUATES A SHELL CONTRIBUTION TO THE IONISATION RATE COEFFICIENT
C   IN THE BURGESS-CHIDICHIMO APPROXIMATION  MNRAS(1983)203,1269.
C   EXCLUDING THE THRESHOLD CORRECTION FACTOR
C
C  CALLING PROGRAM: 
C            SPFMAN11.FOR
C
C  INPUT:
C      Z=TARGET ION CHARGE NUMBER
C      XI=EFFECTIVE IONISATION POTENTIAL FOR SHELL (RYD)
C      ZETA=EFFECTIVE NUMBER OF EQUIVALENT ELECTRONS IN SHELL
C      ENER=ELECTRON ENERGY (RYD)
C
C  OUTPUT:
C      QBCHID=IONISATION CROSS-SECTION (PI*A0**2)
C
C  AUTHOR:
C      H.P SUMMERS, JET            1 JULY 1987
C
C UNIX-IDL CONVERSION:
C
C  VERSION 1.1                                           DATE: 29-08-96
C  MODIFIED: WILLIAM OSBORN, TESSELLA SUPPORT SERVICES PLC.
C		- NO FUNCTIONAL CHANGES TO IBM VERSION.
C
C-----------------------------------------------------------------------
       QBCHID=0.0D0
       IF(ENER.LE.XI)RETURN
       C=2.3D0
       BETA=0.25D0*(DSQRT((100.0D0*Z+91.0)/(4.0D0*Z+3.0D0))-5.0D0)
       T1=ZETA*DLOG(ENER/XI)/(XI*ENER)
       W=(DLOG(ENER/XI))**(BETA*XI/ENER)
C  OMIT THE W THRESHOLD ADJUSTMENT
C      QBCHID=C*T1*W
       QBCHID=C*T1
   10  RETURN
      END
      REAL*8              ENER,        XI,          Z,           ZETA
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