PHOTONUC¶

Summary

Activates gamma, electron and positron interactions with nuclei.

See also LAM–BIAS, MUPHOTON

For all SDUM except ELECTNUC/MUMUPAIR/MUMUPRIM:

WHAT(1) :: flag to switch on nuclear interactions of photons:
≤ -1.0:: resets to default (no photonuclear interactions)
= 0.0:: ignored
= 1.0:: photonuclear interactions are activated at all energies
= 2.0:: photonuclear interactions are activated only in the high energy range (> 0.7 GeV)
= 3.0:: photonuclear interactions are activated only in the energy region of the \(\Delta\) Resonance
= 4.0:: only Quasi-Deuteron interactions are activated
= 5.0:: only Giant Dipole Resonance interactions are activated
≥ 10.0:: interpreted as ih + id*10 + iq*100 + ig*1000

where	`ih = 1`	to activate High-energy interactions
	`id = 1`	to activate \(\Delta\) Resonance
	`iq = 1`	to activate Quasi-Deuteron
	`ig = 1`	to activate Giant Dipole Resonance

and each is = 0.0 otherwise

Default: = 0.0 (no photonuclear interaction)
WHAT(2),: WHAT(3): not used
WHAT(4) =: lower index bound (or corresponding name) of materials where the indicated photonuclear interactions are activated

(“From material ``WHAT(4)``…”)
Default: = 3.0
WHAT(5) =: upper index bound (or corresponding name) of materials where the indicated photonuclear interactions are activated

(“…to particle ``WHAT(5)``…”)
Default: = WHAT(4)
WHAT(6) =: step length in assigning indices

(“…in steps of ``WHAT(6)`` ”)
Default: = 1.0
SDUM: : blank

For SDUM = ELECTNUC:

WHAT(1) :: flag to switch on electronuclear interactions:
≤ -1.0:: resets to default (no electronuclear interactions)
= 0.0:: ignored
= 1.0:: electronuclear interactions are activated at all energies
= 2.0:: electronuclear interactions are activated only in the high energy range (> 0.7 GeV)
= 3.0:: electronuclear interactions are activated only in the \(\Delta\) Resonance energy region
= 4.0:: electronuclear interactions are activated only in the Quasi-Deuteron energy region
= 5.0:: electronuclear interactions are activated only in the Giant Dipole Resonance energy region
≥ 10.0:: interpreted as ih + id*10 + iq*100 + ig*1000

where	`ih = 1`	to activate High-energy interactions
	`id = 1`	to activate \(\Delta\) Resonance
	`iq = 1`	to activate Quasi-Deuteron
	`ig = 1`	to activate Giant Dipole Resonance

and each is = 0.0 otherwise

Default: = 0.0 (no electronuclear interaction)
WHAT(2),: WHAT(3): not used
WHAT(4) =: lower index bound of materials (or corresponding name) where the indicated electronuclear interactions are activated

(“From material ``WHAT(4)``…”)
Default: = 3.0
WHAT(5) =: upper index bound of materials (or corresponding name) where the indicated electronuclear interactions are activated

(“…to particle ``WHAT(5)``…”)
Default: = WHAT(4)
WHAT(6) =: step length in assigning indices

(“…in steps of ``WHAT(6)`` ”)
Default: = 1.0
SDUM: = ELECTNUC

For SDUM = MUMUPAIR/MUMUPRIM:

WHAT(1) :: flag to switch on muon pair production by photons:
= -1: : resets to default (no muon pair production)
= 0: : ignored
> 0: : interpreted as ich + iqe*10 + iin*100 + ids*1000

where	`ich = 1`	to activate muon pair coherent production
	`iqe = 1`	to activate muon pair incoherent quasielastic production
	`iin = 1`	to activate muon pair incoherent inelastic production
	`ids = 1`	to activate muon pair deep inelastic production

and each is = 0.0 otherwise

Default: = 0.0 (no muon pair production by photons)
WHAT(2) :: interaction length biasing factor
= 0.0: : ignored
0 <: |WHAT(2)| < 1 : the interaction length of the photon is reduced by a multiplying factor |WHAT(2)|
1 ≤: |WHAT(2)| : a possible previous biasing factor is reset to the default value (no biasing)
0 <: WHAT(2) < 1 : the primary particle always survives with reduced weight
-1 <: WHAT(2) < 0 : Russian Roulette is played to decide if the primary particle will be killed, or survive with its original weight
Default: : no biasing
WHAT(3) :: not used
WHAT(4) =: lower bound of the indices of materials where the indicated photomuon production mechanisms are activated

(“From material ``WHAT(4)``…”)
Default: = 3.0
WHAT(5) =: upper bound of the indices of materials where the indicated photomuon production mechanisms are activated

(“…to particle ``WHAT(5)``…”)
Default: = WHAT(4)
WHAT(6) =: step length in assigning indices

(“…in steps of ``WHAT(6)`` ”)
Default: = 1.0
SDUM: = MUMUPAIR: photomuon production biasing applied to all photons

MUMUPRIM: photomuon production biasing applied to primaries only
Default: (option PHOTONUC not given): photon or electron interactions with nuclei as well as photomuon production are not simulated

Notes

Muon photonuclear interactions (via virtual photons) are not handled by PHOTONUC but by MUPHOTON.
Because photonuclear and electronuclear cross sections are much smaller than photon cross sections for electromagnetic interactions with atoms and electrons, analogue simulations of photonuclear and electronuclear interactions are very inefficient. Generally, it is recommended to use PHOTONUC in combination with LAM–BIAS to increase artificially the frequency of photonuclear and electronuclear interactions. See Notes 9 and 10 to option LAM–BIAS for more details.
Also photomuon production cross sections are much smaller than photon cross sections for electromagnetic interactions with atoms and electrons, as discussed in Note 2. But in this case, the artificial increase of interactions can be performed directly with the PHOTONUC command (see WHAT(2) with SDUM = MUMUPAIR or MUMUPRIM)

Example 1:

* Giant Resonance and Quasi-Deuteron photonuclear interactions are requested
* in material 18. The photon hadronic interaction length is artificially
* shortened by a factor 0.02 in order to improve statistics
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
PHOTONUC      1100.0       0.0       0.0      18.0       0.0       0.0
LAM-BIAS         0.0      0.02      18.0       7.0       0.0       0.0

Example 2:

* Photonuclear interactions are requested at all energies in materials
* 3, 7, 11 and 15. The photon hadronic interaction length is shortened
* by a factor 0.025
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
PHOTONUC         1.0       0.0       0.0       3.0      15.0       4.0
LAM-BIAS         0.0     0.025       0.0       7.0       0.0       0.0