XN = 1.0E10
      RE = 2.818E-15
      BETAY = 400.
      GAMMA = 1.5E6
      SIGZ = 80.E-6
      C    = 3.0E8
      COND = 59.0E6
      EMITY= 4.8E-8/GAMMA
      SIGY = SQRT(EMITY*BETAY)
      XLMD = 1./COND/120./3.14
 
1     CONTINUE
           
cc      WRITE(6,*) 'Enter radial aperture of the collimator (m)'
cc      READ(5,*) A
cc      IF(A.LT.0.) GO TO 9999
      WRITE(6,*) 'Enter length of the collimator (m)'
      READ(5,*) XLNG
      IF(XLNG.LT.0.) GO TO 9999
      A = 10.*SIGY
      STEP = SIGY
      NTRY = 0
100   CONTINUE      
     
      THETA= ( 2.*XLMD*SIGZ/A/A )**0.25
      
      COEF = 1.77*XN*RE*BETAY/GAMMA
      DELTA= SQRT(XLMD/SIGZ)*(1./THETA/A/A + XLNG/A/A/A )
     *      + 0.69*THETA/A/SIGZ
      DELTA= COEF*DELTA
      
      DDELTA = DELTA**2/2.
      IF(DDELTA.GT.0.01) THEN
      IF(NTRY.GT.0) GO TO 200
      A    = A + STEP
CCC      print *,' +a =',a,'ddelta=',ddelta      
      GO TO 100
      ELSEIF(DDELTA.LT.0.011) THEN
      NTRY= 1
      A   = A - 0.1*STEP
CCC      print *,' -a =',a,'ddelta=',ddelta      
      GO TO 100
      ENDIF

200   CONTINUE            
      WRITE(6,600) XLMD,SIGY,A,A/SIGY,XLNG
     *,THETA,THETA*57.30,DELTA**2/2.
600   FORMAT(1X,'Resitive depth (Cu)=',E14.4,' m'/
     *,      1X,'sigma_y            =',E14.4,' m'/
     *,      1X,'Aperture           =',E14.4,' m (',F6.2,'/sigy )',/
     *,      1X,'Collimator length  =',F6.3,' m',/
     *,      1X,'THETA              =',E14.4
     *,1X,'(',F8.2,' deg.)'/
     *,      1X,'DELTA**2/2         =',E14.4)
     
      GO TO 1
9999  CONTINUE      
      STOP
      END