FLUKA: PART-THRes
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PART-THRes
sets different energy transport cutoffs for hadrons, muons and
neutrinos
See also EMFCUT, LOW-BIAS, THRESHOLd
The meaning of WHAT(1)
depends also on the value of WHAT(5)
.
For WHAT(5)
= 0.0 :
WHAT(1)
< 0.0 : kinetic energy cutoff (GeV)
> 0.0 : momentum cutoff (GeV/c)
For WHAT(5)
>= 1.0 :
WHAT(1)
< 0.0 : gamma cutoff (Lorentz factor, = E/mc**2)
> 0.0 : eta cutoff (= beta*gamma = v/c E/mc**2)
Default
(WHAT(1)
= 0.0): the cutoff is 0 for neutrinos,
and 1.E-14 GeV for neutrons.
For any other hadrons, and for muons:
if option DEFAULTS is missing, or is present with
SDUM
= NEW-DEFAults or SHIELDINg, the default cutoff
kinetic energy is 0.01 GeV.
If SDUM
= HADROTHErapy, ICARUS or PRECISIOn, the default
cutoff kinetic energy is 0.0001 GeV.
If SDUM
= CALORIMEtry, the default cutoff kinetic energy
is = 0.001 * m/m_p GeV (m = particle mass, m_p = proton mass)
In any other case, the default cutoff is 0.050 GeV.
(For e+e- and photons the threshold is set by EMFCUT, see
Note 3 below).
WHAT(2)
= lower bound of the particle id-numbers to which the cutoff
applies ("From particle WHAT(2)
...").
Default
= 1.0
WHAT(3)
= upper bound of the particle id-numbers to which the cutoff
applies ("...to particle WHAT(3)
...").
Default
= WHAT(2)
WHAT(4)
= step length in assigning numbers
("...in steps of WHAT(4)
")
Default
= 1.0.
WHAT(5)
: depending on its value, cutoff values indicated by
WHAT(1)
are assigned to kinetic energy, momentum, gamma or
eta (see WHAT(1)
)
WHAT(6)
= 1.0 restricts the given cutoff to charged particles only
Default
: the cutoff applies to all particles indicated by
WHAT(2-4)
SDUM
: not used
Default
(option PART-THR not given): thresholds as described above
for WHAT(1)
= 0.0.
Notes:
1) If low-energy neutron transport is not requested (explicitly via
LOW-NEUT or implicitly via DEFAULTS), the energy of neutrons
below threshold is deposited on the spot.
2) The total momentum cutoffs of heavy ions are derived from that
of a 4He ion (4-HELIUM) by scaling the latter with the ratios
of the atomic weights of the heavy ions and the 4He ion.
The total momentum cutoffs for light ions (4-HELIUM, 3-HELIUM,
TRITON and DEUTERON) can be defined by PART-THRes. If this is not
done, they are derived from that of a proton by scaling the
latter with the ratios of the atomic weights of the light ions and
a proton.
3) Option PART-THR acts on all particles excepted e+ e- and
photons, while EMFCUT option is used to set to transport electrons,
positrons and photons.
4) When the energy of a heavy charged particle becomes lower than the
cutoff defined by PART-THR, and if such cutoff is lower
than 100 MeV, the particle is not stopped, but is ranged
out to rest in an approximate way. Its kinetic energy is
deposited uniformly over the residual range if the latter
is contained within a single region; otherwise a new residual
range is calculated at each boundary crossing and the residual
kinetic energy is distributed accordingly. If applicable, such
a particle eventually decays at rest or is captured. All other
forms of transport are ignored excepted curved paths in
magnetic fields (multiple scattering, delta ray production,
inelastic or elastic collisions, and INCLUDING DECAY IN
FLIGHT). Magnetic fields are taken into account but only
very roughly, since the continuous slowing down of the
particles is not simulated. Antiprotons and pi-minus are
always ranged out to rest (without allowance for decay) and
made to annihilate on a nucleus.
5) If the cutoff is higher than 100 MeV, however, the
particles are stopped in place without any further treatment.
If this happens at a boundary crossing where the material of
the region entered is vacuum, a printed message warns the
user that energy is being deposited in vacuum.
6) By default the neutron threshold is set at 1.E-14 GeV (1.E-5 eV, the
lowest boundary of the group structure). So, normally it is not
necessary to issue a PART-THR command at all for neutrons.
A note of caution: if a PART-THR has been issued spanning all
particles, it is generally necessary to override it with another one
resetting the threshold for neutrons to 1.E-14 GeV.
As a general rule however, if a neutron transport threshold is
set < 20 MeV, it is rounded to the closest lower group boundary.
* Start_Devel_seq
d.1) As a back compatibility patch, in a run which asks for the 72 group
library (with LOW-NEUT), a neutron PART-THR exactly at 0.0196 GeV
is still interpreted as in old FLUKA versions, namely as the
upper energy of the multi-group library.
* End_Devel_seq
Example:
PART-THR -0.002 1.0 11.0 0.0 0.0 1.0
PART-THR -2.0 13.0 16.0 1.0 1.0 0.0
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