THE EGS5 CODE SYSTEM

! backwards in region 1
!
! | |
! Region 1 | Region 2 | Region 3
! | |
! e- =========> | | e- or photon ====>
! | |
! vacuum | Ta | vacuum
!
! DESCRIPTION - PLAN2P is generally called from subroutine HOWFAR
! whenever a particle is in a region bounded by two planes that
! ARE parallel. Both subroutines PLANE1 and CHGTR are called
! by PLAN2P (the second PLANE1 call is not made if the first
! plane is hit, or if the trajectory is parallel).
!------------------------------------------------------------------
! NPL1 = ID number assigned to plane called first (input)
! NRG1 = ID number assigned to region particle trajectory
! will lead into
! ISD1 = 1 normal points towards current region (input)
! = -1 normal points away from current region (input)
! NPL2 = Same (but for plane called second)
! NRG2 = Same (but for plane called second)
! ISD2 = Same (but for plane called second)
!***********************************************************************
subroutine howfar
implicit none
include ’include/egs5_h.f’
! Main EGS "header" file
include ’include/egs5_epcont.f’ ! epcont contains irnew, ustep
! and idisc
include ’include/egs5_stack.f’ ! stack contains x, y, z, u, v,
! w, ir and np
! ----------------------
! Auxiliary-code COMMONs
! ----------------------
include ’auxcommons/aux_h.f’
! Auxiliary-code "header" file
include ’auxcommons/pladta.f’
integer irl
! Local variable
irl=ir(np)
! Set local variable
if (irl.ne.2) then
idisc=1 ! Terminate this history if not in plate
else
! We are in the Ta plate - check the geometry
call plan2p(irl,irl+1,1,irl-1,irl-1,-1)
end if
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