EMFCUT¶

Summary

Sets the energy thresholds for electron and photon production in different materials, and electron and photon transport cutoffs in selected regions.
It also allows to set an arbitrary energy threshold for all electron and photon interactions managed by EMF ​ on a material basis. This is of course non-physical and it is provided primarily for particular studies where the user wants to switch off selectively a physical process.
Only meaningful when the EMF option is chosen (explicitly or implicitly via option DEFAULTS). ​​ ​​ ​

See also EMF, PART–THR, MATERIAL

For SDUM = PROD–CUT:

|WHAT(1)| =: Energy threshold for electron and positron production in GeV:
> 0.0:: Energy threshold for electron and positron production is expressed as total energy (kinetic plus rest mass)
< 0.0:: Energy threshold for electron and positron production is expressed as kinetic energy
= 0.0:: not allowed
Default: : equal to the lowest electron transport cutoff in all regions made of this material (see Note 1)
WHAT(2) > 0.0:: Energy threshold for \(\rm{\gamma}\) production in GeV
= 0.0:: not allowed
Default: : equal to the lowest photon transport cutoff in all regions made of this material (see Note 1)
WHAT(3) :: FUDGEM parameter. This parameter takes into account the contribution of atomic electrons to multiple scattering. For production and transport cutoffs larger than 100 keV it must be set = 1.0, while in the keV region it must be set = 0.0
Default: : there is no default, 0 is an allowed value but rarely the correct one (see above)
WHAT(4) =: lower bound (or corresponding name) of the FLUKA material number where e\(^{\pm}\) and photon production thresholds respectively equal to WHAT(1) and WHAT(2) apply. The material numbers or names are those pre-defined or assigned using a MATERIAL card.

(“From material ``WHAT(4)``…”)
Default: = 3.0
WHAT(5) =: upper bound (or corresponding name) of the FLUKA material number where \(e^{\pm}\) and photon production thresholds respectively equal to WHAT(1) and WHAT(2) apply. The material numbers or names are those pre-defined or assigned using a MATERIAL card.

(“…to material ``WHAT(5)``…”)
Default: = WHAT(4)
WHAT(6) =: step length in assigning the material number.

(“…in steps of ``WHAT(6)`` ”)
Default: = 1.0
Default: (option EMFCUT with SDUM = PROD–CUT not requested): production cutffs in a material are set equal to the lowest transport cutoffs in the regions with that material.

For SDUM = blank, or PROMPT, or DELAYED:

|WHAT(1)| =: electron and positron transport energy cutoff in GeV. If SDUM = blank, the cutoff refers to all e\(^\pm\); if SDUM = PROMPT, it concerns only prompt ones; if SDUM = DELAYED, only electrons and positrons emitted as decay radiation.
> 0.0:: electron and positron cutoff is expressed as total energy (kinetic plus rest mass)
< 0.0:: electron and positron cutoff is expressed as kinetic energy
= 0.0:: not allowed.

This value can be overridden in the user routine UBSSET by assigning a value to variable ELECUT
Default: : the e\(^\pm\) transport cutoff is set equal to the production threshold for discrete electron interactions
WHAT(2) > 0.0:: photon transport energy cutoff (GeV). If SDUM = blank, the cutoff refers to all photons; if SDUM = PROMPT, it concerns only prompt ones; if SDUM = DELAYED, only photons emitted as decay radiation.
= 0.0:: not allowed.

This value can be overridden in the user routine UBSSET by assigning a value to variable GAMCUT
Default: : the photon transport cutoff is set equal to threshold for photon production by electron bremsstrahlung
WHAT(3): : not used
WHAT(4) =: lower bound (or corresponding name) of the region indices with electron cutoff equal to |WHAT(1)| and/or photon cutoff equal to WHAT(2).

(“From region ``WHAT(4)``…”)
Default: = 2.0
WHAT(5) =: upper bound (or corresponding name) of the region indices with electron cutoff equal to |WHAT(1)| and/or photon cutoff equal to WHAT(2).

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

(“…in steps of ``WHAT(6)`` ”)
Default: = 1.0
Default: (option EMFCUT with SDUM = blank not requested): transport cutoffs in a region are set equal to the production cutoffs in the material of that region.

For SDUM = ELPO–THR:

WHAT(1) > 0.0:: kinetic energy threshold (GeV) for \(\rm{e}^{\pm}\) bremsstrahlung
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(2) > 0.0:: kinetic energy threshold (GeV) for Bhabha/Møller scattering
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(3) > 0.0:: kinetic energy threshold (GeV) for \(\rm{e}^{\pm}\) photonuclear interactions
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(4): – WHAT(6): see below

For SDUM = ANNH–THR:

WHAT(1) > 0.0:: kinetic energy threshold (GeV) for \(e^+\) annihilation
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(2): – WHAT(3): not used
WHAT(4): – WHAT(6): see below

For SDUM = PHOT–THR:

WHAT(1) > 0.0:: energy threshold (GeV) for Compton scattering
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(2) > 0.0:: energy threshold (GeV) for photoelectric effect
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(3) > 0.0:: energy threshold (GeV) for gamma pair production
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(4): – WHAT(6): see below

For SDUM = PHO2–THR:

WHAT(1) > 0.0:: energy threshold (GeV) for Rayleigh scattering
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(2) > 0.0:: energy threshold (GeV) for photonuclear interactions
= 0.0:: ignored
< 0.0:: resets to default
Default: = 0.0
WHAT(3): : not used
WHAT(4): – WHAT(6): see below

For SDUM = ELPO–THR, ANNH–THR, PHOT–THR, PHO2–THR:

WHAT(4) =: lower bound (or corresponding name) of the material indices in which the respective thresholds apply

(“From material ``WHAT(4)``…”)
Default: = 3.0
WHAT(5) =: upper bound (or corresponding name) of the material indices in which the respective thresholds apply.

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

(“…in steps of ``WHAT(6)`` ”)
Default: = 1.0
Default: (option EMFCUT not requested): Transport cutoffs are set equal to production thresholds for discrete electron interactions and for discrete photon production.

Notes

Default values are available for the electron and photon production thresholds in electromagnetic interactions, but they are generated by a complex logic based on possible other settings (transport cutoffs, delta-ray production thresholds, DEFAULTS card, other defaults). It is not always guaranteed that the resulting values be appropriate to the problem of interest. Therefore, in order to have a good control of the physics, the user is recommended to provide explicit threshold values, or at least to check them on the main output.
Electron and positron transport cutoffs (indicated in the main output with Ecut) and photon transport cutoffs (Pcut) are assigned by region, while electron/positron production cutoffs (Ae) and photon production cutoffs (Ap) are assigned by material.

When the transport cutoffs in a given region are larger than those of production for discrete interactions in the corresponding material, particles with energy higher than production thresholds and lower than transport cutoffs are not transported but are still generated (their energy is deposited at the point of production). It is suggested to avoid such a situation unless it is really necessary, as particle generation demands a considerable computer time and partially offsets the gain due to a higher transport cutoff.

When instead the transport cutoffs are lower than the production ones, they are increased to be equal to them.
The minimum threshold energy for transport and production of photons is 100 eV. For electrons and positrons, it is 1 keV.
Different transport cutoffs for prompt and decay e\(^+\)/e\(^-\)/\(\gamma\) can be set also by WHAT(5) of command RADDECAY, but only identically for all regions, while EMFCUT with SDUM = PROMPT or DELAYED can be tuned per region.

Example 1 (number-based):

*...+....1....+....2....+....3....+....4....+....5....+....6....+....7...
EMFCUT       -1.0E-5    1.0E-5       0.0       4.0       8.0          PROD-CUT
*   A production threshold of 10 keV is set for electrons, positrons and
*   photons in all materials from 4 to 8.

The same example, name-based:

EMFCUT       -1.0E-5    1.0E-5       0.0    HELIUM    OXYGEN          PROD-CUT

Example 2 (number-based):

EMFCUT        -0.002     2.E-4       1.0       1.0      15.0
EMFCUT       -1.0E-4     1.E-5      -1.0       7.0      11.0       2.0
*   A kinetic energy transport cutoff for electrons and positrons is set
*   at 100 keV in regions 7, 9 and 11 and at 2 MeV in all other regions from 1
*   to 15. Photon transport cutoff is set equal to 10 keV in regions 7, 9, 11
*   and to 200 keV in the other regions.

The same example, name-based, assuming that the 15 regions are all the regions of the problem:

::

EMFCUT -0.002 2.E-4 1.0 FirstReg @LASTREG EMFCUT -1.0E-4 1.E-5 -1.0 Seventh Eleventh 2.0