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Common /GCPHYS/

The variables described above are stored in the common /GCPHYS/, one process per line:

      COMMON/GCPHYS/IPAIR,SPAIR,SLPAIR,ZINTPA,STEPPA
     +             ,ICOMP,SCOMP,SLCOMP,ZINTCO,STEPCO
     +             ,IPHOT,SPHOT,SLPHOT,ZINTPH,STEPPH
     +             ,IPFIS,SPFIS,SLPFIS,ZINTPF,STEPPF
     +             ,IDRAY,SDRAY,SLDRAY,ZINTDR,STEPDR
     +             ,IANNI,SANNI,SLANNI,ZINTAN,STEPAN
     +             ,IBREM,SBREM,SLBREM,ZINTBR,STEPBR
     +             ,IHADR,SHADR,SLHADR,ZINTHA,STEPHA
     +             ,IMUNU,SMUNU,SLMUNU,ZINTMU,STEPMU
     +             ,IDCAY,SDCAY,SLIFE ,SUMLIF,DPHYS1
     +             ,ILOSS,SLOSS,SOLOSS,STLOSS,DPHYS2
     +             ,IMULS,SMULS,SOMULS,STMULS,DPHYS3
     +             ,IRAYL,SRAYL,SLRAYL,ZINTRA,STEPRA
      COMMON/GCPHLT/ILABS,SLABS,SLLABS,ZINTLA,STEPLA
     +             ,ISYNC
     +             ,ISTRA
*

The first 9 processes (from PAIR production up to MUon NUclear interaction) and the RAYLeigh scattering and Light ABSorbtion have the same scheme. Let's take as an example the first one (for a complete description of the common see [BASE030]):

IPAIR

flag for secondaries:

0=: the process is turned off;
1=: generation of secondaries enabled;
2=: no generation of secondaries.

SPAIR

N

_λλ(x) &sp;= &sp;

remaining track-length before interaction, evaluated at the last point where the mechanism was active, i.e. IPAIR $≠0$ .

SLPAIR

track length at the time when the interaction last happened for the current particle. Only SLPAIR (direct pair production by

μ

), SLDRAY (

δ

-ray production), SLBREM (bremsstrahlung for

μ

), SLHADR (hadronic interactions), SLMUNU (muon-nucleus interactions) and SLRAYL (Rayleigh effect) are used. The variables SOLOSS, STLOSS, SOMULS, STMULS are obsolete. They have been kept for backward compatibility, but their value is undefined and should not be used.

ZINTPA

N

_λ&sp;= &sp; remaining number of interaction lengths (mean free paths) evaluated at the last point where the mechanism was active, i.e. IPAIR

≠0

STEPPA

λ(x) &sp;= &sp;

value of the interaction length at the last point where the mechanism was active, i.e. IPAIR

≠0

;

The evaluation and update of the quantities like STEPPA, SPAIR and ZINTPA are turned off in the media where the mechanism is not active (

IPAIR≠0

). Turning off a mechanism in one tracking medium may give incorrect physics results because not only will the mechanism not be active, but the interaction probabilities will not be updated, as if that medium had not been traversed at all. This feature of the tracking routines is used mainly in the vacuum, (defined as a medium with atomic number

Z< 1

), where all the mechanisms but DECAy (and SYNChrotron radiation, if activated) are inactive.

The DECAy in flight is simpler since the mean life time of the particle, $τ$ , is not material dependent and can be sampled directly.

SLIFE: not used.
SUMLIF: proper time left before the decay. At the beginning of the track $SUMLIF&sp;= &sp;-cτlog( η)$ .
SDCAY: distance left to decay point evaluated at the last point where the mechanism was active, i.e. $IDECA≠0$ .

Next: Cross-sectionenergy loss Up: PHYS010 Compute the Previous: Determination of the

Janne Saarela
Mon Apr 3 12:46:29 METDST 1995