ADAS Subroutine rbchid

       FUNCTION RBCHID(Z,XI,ZETA,TE)

       IMPLICIT REAL*8(A-H,O-Z)

C  PURPOSE: EVALUATES A SHELL CONTRIBUTION TO THE IONISATION RATE
C  COEFFICIENT IN THE BURGESS-CHIDICHIMO APPROXIMATION
C
C  MNRAS(1983)203,1269.
C
C      Z=TARGET ION CHARGE NUMBER
C      XI=EFFECTIVE IONISATION POTENTIAL FOR SHELL (RYD)
C      ZETA=EFFECTIVE NUMBER OF EQUIVALENT ELECTRONS IN SHELL
C      TE=ELECTRON TEMPERATURE (K)
C UNIX-IDL PORT:
C	   WILLIAM OSBORN, TESSELLA SUPPORT SERVICES PLC.
C
C DATE:    22ND APRIL 1996
C
C VERSION: 1.1				DATE: 22-04-96
C MODIFIED: WILLIAM OSBORN
C	    - FIRST VERSION. NO CHANGES TO IBM CODE.
C
C VERSION: 1.2				DATE: 16-05-07
C MODIFIED: Allan Whiteford
C	    - Updated comments as part of subroutine documentation
C             procedure.
C
C-----------------------------------------------------------------------

       RBCHID=0.0D0
       C=2.3D0
       BETA=0.25D0*(DSQRT((100.0D0*Z+91.0)/(4.0D0*Z+3.0D0))-5.0D0)
       ATE=1.5789D5/TE
       Y=ATE*XI
C      WRITE(6,1001) ATE,XI,Y
C      WRITE(7,1001) ATE,XI,Y
 1001  FORMAT(1H0,' ATE,XI,Y = ',1P,3D12.2)
       IF(Y.GT.150.0D0)GO TO 10
       T1=ZETA*DSQRT(Y)*DEXP(-Y)*EEI(Y)/XI**1.5D0
       P=1.0D0+1.0D0/Y
       W=(DLOG(P))**(BETA/P)
       RBCHID=2.1715D-8*C*T1*W
   10  RETURN
      END
      REAL*8              TE,          XI,          Z,           ZETA