Physics  settings

If you simply use a standard keys, the following standard settings are possible, selected with one of the following keyword in  dept geometry command:

 Hadr_on  -  all Geant Physics On. Then this option is applied to the geometry.g, the values of flags are:

IDCAY, IANNI, IBREM, ICOMP, IHADR, IMUNU, IPAIR, IPHOT, ILOSS, IDRAY, IMULS  equal to 1,
IRAYL, ISTRA equal to 0.

IDCAY, IANNI, IBREM, ICOMP, IMUNU, IPAIR, IPHOT, ILOSS, IDRAY, IMULS  equal to 1,
IHADR, IRAYL, ISTRA equal to 0.

IDCAY, IMULS  equal to 1,
IANNI, IBREM, ICOMP, IHADR, IMUNU, IPAIR, IPHOT, IDRAY, IRAYL, ISTRA equal to 0,
ILOSS  equal to 2. (No separate delta rays are generated).

IDCAY, IANNI, IBREM, ICOMP, IHADR, IMUNU, IPAIR, IPHOT, IDRAY, IMULS, IRAYL, ISTRA equal to 0,
ILOSS  equal to 2. (No separate delta rays are generated).

process_name flag_value

These commands set the appropriate variable in the /GCKING/ common block as the described in the  GEANT3 manual (see except below).

For example, if you use option Hadr_on and  need to study multiple scattering effect, you can get a sample with no scattering
at all by typing:

MULS    0

Do not forget to issue gclose allcommand after you redefine some of the default values - these command forces GEANT to recalculate process cross-section according to your modifications.

Here we describe briefly the meaning of different process flags as they are understood by GEANT.  For more details see the  GEANT3 manual .
As a general rule if the variable is set to

• 0 The process is completely ignored.
• 1 The process is considered and possible secondary particles generating from the interaction are put into the /GCKING/ common. If the interacting particle disappears in the interaction, then the process is stopped with ISTOP=1 (common /GCTRAK/)
• 2 The process is considered. If secondary particles result from the interaction, they are not generated and their energy is simply added in the variable DESTEP (common /GCTRAK/). If the interacting particle disappears in the interaction, the variable ISTOP is set to 2.

Keyword        Related process
DCAY

Decay in flight. The decaying particle stops. The variable IDCAY controls this process. See [CONS310, PHYS400].
0 - No decay in flight.
1 - Decay in flight with generation of secondaries. Default setting.
2 - Decay in flight without generation of secondaries.

MULS

Multiple scattering. The variable IMULS controls this process. For more information see [PHYS320 or 325 or 328].
0 - No multiple scattering.
1 - Multiple scattering according to Molière theory. Default setting.
2 - Same as 1. Kept for backward compatibility.
3 - Pure Gaussian scattering according to the Rossi formula.

Nuclear fission induced by a photon. The photon stops. The variable IPFIS controls this process. See [PHYS240].
0 - No photo-fission. Default setting.
1 - Photo-fission with generation of secondaries.
2 - Photo-fission without generation of secondaries.

Muon-nucleus interactions. The muon is not stopped. The variable IMUNU controls this process. See [PHYS431] for more details.
0 - No muon-nucleus interactions.
1 - Muon-nucleus interactions with generation of secondaries. Default setting.
2 - Muon-nucleus interactions without generation of secondaries.

Continuous energy loss. The variable ILOSS controls this process.
0 - No continuous energy loss, IDRAY is set to 0.
1 - Continuous energy loss with generation of delta rays above DCUTE (common/GCUTS/) and restricted Landau fluctuations below  DCUTE.
2 - Continuous energy loss without generation of delta rays and full Landau-Vavilov-Gauss fluctuations. In this case the variable IDRAY is forced to 0 to avoid double counting of fluctuations. Default setting.
3 - Same as 1, kept for backward compatibility.
4 - Energy loss without fluctuation. The value obtained from the tables is used directly.

Photoelectric effect. The interacting photon is stopped. The variable IPHOT controls this process. More info [PHYS230].
0 - No photo-electric effect.
1 - Photo-electric effect with generation of the electron. Default setting.
2 - Photo-electric effect without generation of the electron.

Compton scattering. The variable ICOMP controls this process. For additional information see [PHYS220].
0 - No Compton scattering.
1 - Compton scattering with generation of e^-. Default setting.
2 - Compton scattering without generation of  e^-.

Pair production. The interacting gamma is stopped. The variable IPAIR controls this process. More info [PHYS210]
0 - No pair production.
1 - Pair production with generation of e^-/e⁺. Default setting.
2 - Pair production without generation of  e^-/e⁺.

Bremsstrahlung. The interacting particle e⁺, e^-, mu⁺, mu^-  is not stopped. The variable IBREM controls this process. More details in [PHYS340].
0 - No bremsstrahlung.
1 - bremsstrahlung with generation of  gamma. Default setting.
2 - bremsstrahlung without generation of gamma.

Rayleigh effect. The interacting  gamma is not stopped. The variable IRAYL controls this process. See [PHYS250] for details.
0 - No Rayleigh effect. Default setting.
1 - Rayleigh effect.

delta ray production. The variable IDRAY controls this process. See [PHYS430]
0 - No delta rays production.
1 - delta rays production with generation of . Default setting.
2 - delta rays production without generation of .

Positron annihilation. The  e⁺ is stopped. The variable IANNI controls this process. For reference see [PHYS350].
0 - No positron annihilation.
1 - Positron annihilation with generation of photons. Default setting.
2 - Positron annihilation without generation of photons.

Hadronic interactions. The particle is stopped in case of inelastic interaction, while in case of elastic  interaction it is not stopped. To simulate the interactions of hadrons with the nuclei of the matter traversed, four alternatives are provided:
1. The generator of the FLUKA  hadron shower MonteCarlo and the interface routines to GEANT. See [PHYS520] for more information.
2. The generator of the GHEISHA  hadron shower MonteCarlo and the interface routines to GEANT. See [PHYS510] for more details.
3. The generator of the MICAP  hadron shower MonteCarlo and the interface routines to GEANT.
4. The generator of the GCALOR  hadron shower MonteCarlo and the interface routines to GEANT.

The variable IHADR controls this process.
0 - No hadronic interactions.
1 - Hadronic interactions with generation of secondaries using GHEISHA package. Default setting.
2, 3 - Same as 1.
4 - Hadronic interactions are simulated using FLUKA package.
5 - Hadronic interactions are simulated using MICAP package.
6 - Hadronic interactions are simulated using GCALOR package.

Light ABSorption. This process is an absorption of light photons (particle type 7) in dielectric materials. It is turned on by default when the generation  of Cerenkov light is requested (data record CKOV). For more information see [PHYS260].
This process controlled by ILABS.
0 - No absorption of photons.
1 - Absorption of photons with possible detection.

This flag turns on the collision sampling method to simulate energy loss in thin materials, particularly gases.  For more information see [PHYS334].
The control variable is ISTRA .
0 - Collision sampling is switched off. Default setting.
1 - Collision sampling is activated.

Synchrotron radiation in magnetic field. Defined by variable ISYNC. See [PHYS360].
0 - The synchrotron radiation is not simulated. Default setting.
1 - Synchrotron photons are generated, at the end of the tracking step.
2 - Photons are not generated, the energy is deposited locally.
3 - Synchrotron photons are generated, distributed along the curved path of the particle.

Particle decay modes are coded in GEANT as follows:
 

1NEXT particle has reached the boundary of current volume	2 MULS multiple scattering	3 LOSS continuous energy loss	4 FIEL bending in magnetic field	5 DCAY particle decay	6  PAIR photon pair-production or muon direct pair production	7 COMP Compton scattering	8 PHOT photoelectric effect	9 BREM bremsstrahlung	10 DRAY δ -ray production
11 ANNI positron annihilation	12 HADR hadronic interaction	13 ECOH hadronic elastic coherent scattering	14 EVAP nuclear evaporation	15 FISS nuclear fission	16 ABSO nuclear absorption	17 ANNH anti-proton annihilation	18 CAPT neutron capture	19 EINC hadronic elastic incoherent scattering	20 INHE hadronic inelastic scattering
21 MUNU muon-nuclear interaction	22 TOFM exceeded time of flight cut	23 PFIS nuclear photo-fission	24 SCUT particle due to bending in magnetic field was unexpectedly crossing volume boundaries and  step has been halved to avoid      this	25 RAYL Rayleigh effect	26 PARA parametrisation activated	27 PRED error matrix computed	28 LOOP not used	29 NULL no mechanism is active, usually at the entrance of a new volume	30 STOP Particle has fallen below energy threshold and tracking stops
31 LABS Cerenkov photon absorption	32 LREF Cerenkov photon reflection/refraction	33 SMAX step limited by STEMAX	34 SCOR  correction against loss of precision in boundary crossing	35 CKOV Cerenkov photon generation	36 REFL Cerenkov photon reflection	37 REFR Cerenkov photon refraction	38 SYNC synchrotron radiation generation	39 STRA PAI or ASHO model used for energy loss fluctuations

(for the processes not described here, please refer to the GEANT manual).

Besides of  physics settings described in the previous section, user can specify the value of each available physics cut by means of
CUTS  command. The usage of this command is:

CUTS[cutgam cutele cuthad cutneu cutmuo bcute bcutm dcute dcutm ppcutm tofmax gcuts]

If no parameter is given, the list of the current cuts is printed. The meanings of the parameters listed above are:

cutgam -  "cut for gammas". The default GEANT value is 0.001.
cutele   - "cut for electrons". The default GEANT value is 0.001.
cuthad  - "cut for charged hadrons". The default GEANT value is 0.01.
cutneu  - "cut for neutral hadrons". The default GEANT value is 0.01.
cutmuo - "cut for muons". The default GEANT value is 0.01.
bcute    - "cut for electron brems". The default GEANT value is -1.
bcutm   - "cut for muon brems". The default GEANT value is -1.
dcute    - "cut for electron delta-rays". The default GEANT value is -1.
dcutm   - "cut for muon delta-rays". The default GEANT value is -1.
ppcutm- "cut for e+e- pairs by muons". The default GEANT value is 0.01.
tofmax - "time of flight cut". The default GEANT value is 1.E+10.
gcuts    - "5 user words". Default is 0.

If you are running standard  GSTAR session  for all cuts default value is 0.001, which means 1 MeV threshold for all particles. If the
default values for bcutm, bcutm, dcute, dcutm are not modified, they will be set to cutgam, cutele  respectively. If one of
parameters from cutgam to ppcutm included is modified, cross-section and energy loss tables must be recomputed via command  physi. In GSTAR for this purpose user should use the command

gclose all