ZGOUBI USERS' GUIDE - HEP

4.3 Declaration of options 53·{N$§7>77>'''2ZφθZ 1,21Y1,2YMP 2P 1T 1T 2X1,2XFigure 7: At "$ "e position, particle 1 decays into 2 and 3; zgoubi then calculates the trajectoryof 2, while 3 is discarded.and are the scattering angles of particle 2 relative to the direction of the incoming particle 1;Åthey transform to ¥ and in zgoubi frame.2 "$¤ In ESL and CHANGREF, is compared to at the end of the element. If the decay occurs inside the element,the particle is considered as having decayed at its actual limit path length , and its coordinates at are recalculated bytranslation.< GThe limit path length of all particles (¤ For the same purpose (e.g., use of HISTO), any particle of type 2 (resulting from decay of 1) will be tagged with anat the decay point are stored in"$¤ FDES , ., IMAX ) is stored in the arrayGFDESqstanding for “secondary”. When a particle decays, its O coordinates , , , ¥|{,"$¤ , for further statistical purposes." qNOTE on negative drifts:The use of negative drifts with MCDESINT is allowed and correct. For instance, negative drifts may occur in a structurefor some of the particles when using CHANGREF (due to the -axis rotation or negative XCE), or when using DRIFT§„¨ ïª\with . Provision has been made to take it into account during the MCDESINT procedure, as follows.If, due to a negative drift, a secondary particle reaches back the decay spot of the primary particle from which it originated,then that primary particle is regenerated with its original coordinates at that spot. Then the secondary particle is discardedwhile ray-tracing resumes in a regular way for the primary particle which is again susceptible of decay at the same time-offlight.This procedure is made possible by prior storage of the coordinates of the primary particles (in array "$¤ FDES )each time a decay occurs.Negative steps (XPAS ï \ ) in optical elements are not compatible with MCDESINT.}{