subroutine generate_xy (event_type, x, y)

      implicit NONE

c  constants

      real        pi
      parameter   (pi = 3.14159265)
      real        r0
      parameter   (r0 = 2.)
      real        sigma
      parameter   (sigma = 0.5)

c  arguments

      integer     event_type
      real        x, y

c  local variables

      real        r, theta, x0, y0
      
c  begin

      if ( event_type .eq. 1 ) then

         call RNORML (x,1)
         call RNORML (y,1)
         x = x*sigma
         y = y*sigma

      elseif ( event_type .eq. 2 ) then

         call RANMAR (r,1)
         theta = r*pi*0.7
         x0 = r0*COS(theta)
         y0 = r0*SIN(theta)
         call RNORML (x,1)
         call RNORML (y,1)
         x = x0 + x*sigma
         y = y0 + y*sigma

       endif

       return
       END