PHOTONUC card, SDUM=MUMUPAIR, biasing, suppress the photon

Physics, Transport and Magnetic Fields
3

Dear @acelenta ,

Thank you for your question. If I understand it correctly, it is not possible to activate the bias in the PHOTONUC card (SDUM=MUMUPAIR) without activating at least the Russian Roulette to create a photon replica.

Nevertheless, you can achieve that feature by means of user routines which prevent the replica from being transported. This would be performed in two steps:

  1. First, the photon replica should be identified, for which the following points are important:

    • The photon is created during the bias stage, after the interaction, so it can not be accessed by mdstck.f. Hence, it must be flagged later, when it is loaded in the stack, by means of stupre.f and the variable LOUEMF.
    • In order to identify the pair production, the event flag LPAIRP from evtflg.inc can be used. However, in order to differentiate it from the electron-positron pair production, one can use the fact that the muon pair production implies no variation in the EMF stack (no electrons, positrons or photons involved) and then NPEMF=NPSTRT.

Hence, I suggest you insert the following IF condition in stupre.f:

52       CONTINUE
           LOUEMF(NPNW) = LLOUSE
           
           IF ( LPAIRP .AND. (NPEMF .EQ. NPSTRT) ) THEN
              LOUEMF(NPNW) = 1
           END IF

500 CONTINUE
  1. Once properly identified, the photon replica can be discarded while being transported by means of usrmed.f (activated with the MAT-PROP card). The variable LOUEMF becomes LLOUSE in trackr.inc (to be added explicitly) so that you can include in usrmed.f these lines:
INCLUDE 'trackr.inc'
IF ( LLOUSE .EQ. 1 ) THEN
   WEE = ZERZER
END IF

Please let me know if this helps.
Best regards,

Mario Sacristan

2 Likes