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
> 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 "abcdefghi", where each "a-i" digit is
interpreted as follows (but see Note below):
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 cut-offs, 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 below):
xxxxx * 0.1 = transport energy cut-off multiplication factor for
beta+, beta- and gamma decay radiation
yyyyy * 0.1 = transport energy cut-off multiplication factor for
prompt e+, e- and gamma radiation
= 0.0: ignored
< 0.0: reset to default
Default: e+, e- and gamma transport energy cut-offs 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 cut-offs
Notes:
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 below).
In both cases, the emitted particles are transported like all other
secondaries, within the same run.
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).
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 cut-offs (see Note below).
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.
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.
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.
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...
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 cut-offs 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.
