Last version:
FLUKA 2021.2.2, September 25th 2021
(last respin )
flair-2.3-0b 30-Jul-2021


-- Fluka Release
( 25.09.2021 )

FLUKA 2021.2.2 has been released.
Fluka Release 30.07.2021 FLUKA 2021.2.1 has been released.
Fluka Major Release 18.05.2021 FLUKA 2021.2.0 has been released.
Congratulations from INFN: ,
Dear Paola,
I wish to congratulate you and all the authors and collaborators for this new Fluka release, which looks at the future and confirms the support of INFN in the development and continuous improvement of this code.
best regards
Diego Bettoni
INFN Executive Committee

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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
             Default = no radioactive decays

     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
                          radiation only
                    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
                      b = hadron/muon leading particle  biasing (not defined at
                          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
                    decay radiation (equivalent to 0001000010.)

     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

     Default (option RADDECAY not given): no radioactive decay is activated, and
             no multiplication factors are applied to transport energy cutoffs


  • 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.)


 * In this example, radioactive decays are activated for requested cooling
 * times, with an approximated isomer production. Each radioactive nucleus
 * produced will be duplicated.
 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.

© FLUKA Team 2000–2021

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