Last version:
FLUKA 2021.2.5, February 18th 2022
(last respin )
flair-2.3-0b 30-Jul-2021

News:

-- Fluka Release
( 18.01.2022 )

FLUKA 2021.2.5 has been released.

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requests simulation of radioactive decays and sets the corresponding biasing and transport conditions

     WHAT(1) = flag for activating radioactive decays
= 1: radioactive decays activated for requested cooling times
> 1: radioactive decays activated in semi-analogue mode
= 0: ignored
< 0: reset to default


     WHAT(2) = flag for "patching" isomer production, while waiting for a better
production model
> 0: isomer production "patching" activated
< 0: isomer production "patching" disabled
= 0: ignored
Default: activated if non-analogue radioactive decays is requested,
disabled otherwise


     WHAT(3) = number of "replicas" of the decay of each individual residual
= 0: ignored
< 0: reset to default
Default: 1 for analogue decays, 3 otherwise


     WHAT(4) = switch for applying various biasing features only to prompt
particles, or only to particles originated in radioactive decays,
or to both
> 0.0: a 9-digit number äbcdefghi", where each ä-i" digit is
interpreted as follows (but see Note 4):
0.0 = ignored
1.0 = the corresponding biasing is applied to prompt
2.0 = applied to decay radiation only
3.0 = applied to both prompt and decay radiation
and the digit position is interpreted as follows:
a = hadron/muon interaction length or decay biasing, as
defined by command LAM-BIAS
the moment)
c = hadron/muon importance and Weight Window biasing, as
defined by commands BIASING and WW-FACTOr
d = e+/e-/gamma interaction length biasing, as defined by
command EMF-BIAS
e = e+/e-/gamma leading particle biasing, as defined by
command EMF-BIAS
f = e+/e-/gamma importance and Weight Window biasing, as
defined by commands BIASING and WW-FACTOr
g = low-energy neutron biased downscattering, as defined
by command LOW-DOWN, and non-analogue absorption, as
defined by LOW-BIAS
h = no meaning for the time being
i = low-energy neutron importance and Weight Window
biasing, as defined by commands BIASING and WW-FACTOr
= 0.0: ignored
< 0.0: reset to default
Default: all biasing is applied to prompt showers only (equivalent
to 111111111.)


     WHAT(5) = multiplication factors to be applied to e+/e-/gamma transport
energy cutoffs, respectively for prompt and decay radiation
> 0.0: a 10-digit number xxxxxyyyyy, where the first and the last 5
digits are interpreted as follows (see Note 5):
xxxxx * 0.1 = transport energy cutoff multiplication factor for
beta+, beta- and gamma decay radiation
yyyyy * 0.1 = transport energy cutoff multiplication factor for
prompt e+, e- and gamma radiation
= 0.0: ignored
< 0.0: reset to default
Default: e+, e- and gamma transport energy cutoffs are unchanged:
the multiplication factors are set = 1.0 for both prompt and


     WHAT(6) = flag for generating beta+/beta- spectra with Coulomb and
screening corrections.
> 0.0: Coulomb and screening corrections activated
= 0.0: ignored
< 0.0: Coulomb abd screening corrections ignored
Default: Coulomb and screening corrections are considered


     SDUM    = not used

no multiplication factors are applied to transport energy cutoffs


Notes:

• 1) FLUKA allows for two different ways of simulating radioactive decay. In the semi-analogue mode, (WHAT(1) >
• 1) each single radioactive nucleus is treated in a Monte Carlo way like all other unstable particles: a random decay time, random daughters, random radiation are selected and tracked. This allows for event-by-event analysis, with the time structure recorded in the particles age variable. It is called semi-analogue because the radiation spectra are inclusive (i.e. no correlated $\gamma$ cascade is reproduced, etc.) In the äctivation study" mode (WHAT(1)=1) the time evolution is calculated analytically and all daughter nuclei and all associated radiation are considered, but at fixed times. (See Note 6). In both cases, the emitted particles are transported like all other secondaries, within the same run.

• 2) In the analytical evolution, each radioactive nucleus can be "decayed" several times, in order to improve statistics on, for instance, energy deposition, as set by WHAT(3).

• 3) Although FLUKA allows to simulate in a same run the transport of cascade particles and that of particles generated by decay of the produced residual nuclei, transport and biasing need in general to be set at very different levels. For instance, in a study of induced activity due to photonuclear reactions, it is recommended to set the photon transport threshold not lower than the photonuclear reaction threshold. However, gammas produced in the decay of those residual nuclei have in general lower energies and need to be transported with much lower energy cutoffs (see Note 5 below).

• 4) Biasing can be applied to radiation products. At present, for the biasing switch represented by WHAT(4), only the d, e and f choices are relevant since only beta+, beta- and gamma decays are considered for the time being.

• 5) Both multiplication factors imbedded in WHAT(5) must be >= 1.0. If any of the multiplication factors is set to a value larger than 9999.0, it is effectively considered as infinite, i.e., WHAT(5) = 0000099999. will kill the electromagnetic cascade in the prompt part, while leaving it untouched in the decay part. WHAT(5) = 9999900000. will do the opposite.

• 6) It is possible to perform on-line time evolution of decay radiation, and to score all standard quantities (energy deposition, residuals...) according to a user-defined irradiation profile (IRRPROFI command) and one or more user-defined decay times (DCYTIMES command). Radiation transport will be performed only once, and the evolution will be applied as a weight depending on the setting of the estimator, to be defined with the DCYSCORE command.

• 7) If decays are simulated in semi-analogue mode, detector results are expressed per unit primary weight (possibly scoring together prompt and decay particles, if requested by DCYSCORE with WHAT(1) = -1.0). If decays are instead calculated for requested cooling times, the results are expressed per unit time (Sv/s, cm-2/s, Bq, etc.)

Example:

 * In this example, radioactive decays are activated for requested cooling
* times, with an approximated isomer production. Each radioactive nucleus
* produced will be duplicated.
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
RADDECAY         1.0       1.0       2.0   111000.      200.
* Any biasing of electrons, positrons and photons is applied only to
* prompt particles in the electromagnetic shower, and not to beta and
* gamma particles from radioactive decay.
* The transport energy cutoffs set by EMFCUT (or by DEFAULTS) are
* applied as such to decay betas and gammas, but are multiplied by a
* factor 20 when applied to prompt particles.