FLUKA: RADDECAY
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RADDECAY
requests simulation of radioactive decays and sets the corresponding
biasing and transport conditions
See also DCYTIMES, DCYSCORE, IRRPROFI
WHAT(1)
= flag for activating radioactive decays
= 1: radioactive decays activated for requested cooling times
= 2: radioactive decays activated in semi-analogue mode
= 0: ignored
= -1: reset to default
Default
= no radioactive decays
WHAT(2)
= flag for "patching" isomer production, while waiting for a better
production model
= 1: isomer production "patching" activated
= -1: 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 "abcdefghi", where each "a-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
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 "activation
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 (pSv/s, cm-2/s, Bq, etc.)
8) When the source is a radioactive isotope (defined by command BEAM with
SDUM
= ISOTOPE and by command HI-PROPErt), RADDECAY must be used in
semi-analogue mode (WHAT(1)
> 1). The detector results are then
expressed per isotope decay. Note that command DCYSCORE must be issued
with WHAT(1)
= -1, and must be applying to all relevant estimators
and detectors. Without DCYSCORE, no scoring will occur (see Note 8 to
command BEAM).
9) Different transport cutoffs for prompt and decay e+/e-/gamma can be set
also differently for each region by command EMFCUT with SDUM
= PROMPT or
DELAYED. With WHAT(5)
of RADDECAY it is possible only to define a ratio,
identical for all regions.
Example:
RADDECAY 1.0 1.0 2.0 111000. 200.
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