activates low-energy neutron transport
(see also LOW-MAT, LOW-BIAS)
WHAT(1) = number of neutron groups in the cross-section set used.
The ENEA standard neutron library has 72 groups (see 10}).
Default = 72
WHAT(2) = number of gamma groups
No default if WHAT(1) is given, 22 otherwise. (The ENEA
neutron library has 22 gamma groups).
WHAT(3) = maximum energy of the low-energy cross-section neutron library.
For the ENEA neutron library, the maximum energy is 0.0196 GeV.
Note that rounding (for instance 20 MeV instead of 19.6)
is not allowed!
Default = 0.0196 GeV.
WHAT(4) = printing flag: from 0.0 to 3.0 increases the amount of
output about cross-sections, kerma factors, etc.
1.0 : Standard output includes integral cross sections,
kerma factors and probabilities
2.0 : In addition, downscattering matrices and group
neutron-to-gamma transfer probabilities are printed
3.0 : In addition, scattering probabilities and angles are
printed
Default: 0.0 (minimum output)
WHAT(5) = number of neutron groups to be considered thermal ones. (The
ENEA neutron library has one thermal group).
= 0, ignored
< 0: resets to the default = 1.0
Default = 1.0
WHAT(6) = i0 + 10 * i1:
i0 = 1: available pointwise cross sections used (see Note
below) and explicit and correlated 6-Li(n,gamma)7-Li,
10-B(n,t gamma)4-He, 40-Ar(n,gamma)41-Ar,
x-Xe(n,gamma)x+1-Xe and 113-Cd(n,gamma)114-Cd
photon cascade requested
= 0: ignored
=<-1: resets to the default (pointwise cross sections
are not used)
i1 = 1, fission neutron multiplicity forced to 1, with
proper weight
= 0, ignored
=<-1: resets to the default (normal fission multiplicity)
Default = -11., unless option DEFAULTS is present with
SDUM = CALORIMEtry, ICARUS, NEUTRONS or PRECISIOn,
in which case the default is 1.0 (pointwise cross sections
are used when available and fission multiplicity is not
forced)
SDUM: Not used
Default (option LOW-NEUT not given): if option DEFAULTS is used with
SDUM = CALORIMEtry, EET/TRANsmut, HADROTHErapy, ICARUS, NEUTRONS,
NEW-DEFAults, PRECISIOn or SHIELDINg, low-energy neutrons are
transported and a suitable cross section library must be
available.
In all other cases, low-energy neutrons are not transported, and
their energy is deposited as explained in the note below.
Notes: Evaporation option is mandatory by default or explicitly
(see EVENTYPE) if LOW-NEUT is requested (by default or
explicitly).
If low-energy neutrons are not transported (because of the chosen
DEFAULTS, or because a DEFAULTS card is absent), the energy
of neutrons below threshold (default or set by PART-THR)
is deposited on the spot.
This is true also for evaporation neutrons.
If there is no interest in low-energy neutron transport, but that
feature is implicit in the DEFAULTS option chosen, it is suggested
to use LOW-BIAS with a group cutoff WHAT(1) = 1.0.
Gamma data are used only for gamma generation and
not for transport (transport is done via the FLUKA
ElectroMagnetic module EMF using continuous cross sections).
The actual precise energy of a photon generated by (n,gamma)
or by inelastic reactions such as (n,n') is sampled randomly within
the gamma energy group concerned, except for a few important
reactions where a single monoenergetic photon is emitted. By
default, for the 1-H(n,gamma)2-H reaction the actual photon energy
of 2.226 MeV is used. It is possible to do the same with the
capture gammas in 6-Li, 10-B, 40-Ar, x-Xe and 113-Cd, by
setting WHAT(6) = 1.0 or 11.0.
Pointwise neutron transport is available, by setting
WHAT(6) = 1.0 or 11.0, for the following nuclides: 1-H (above
10 keV), 6-Li (all reactions), 10-B (only for the reaction
10-B(n,t gamma)4-He). Recoil protons are always transported
explicitly, and so is the proton from the 14-N(n,p) reaction,
for which a pointwise treatment is always applied
The groups are numbered in DECREASING energy order (see 10}
for a detailed description).
Note that the energy limits of the thermal neutron group
in the ENEA neutron library are:
1.E-14 GeV (1.E-5 eV) and 4.14E-10 GeV (0.414 eV)
Here are the settings for transport of low-energy neutrons
corresponding to available DEFAULTS options:
CALORIMEtry, ICARUS, NEUTRONS, PRECISIOn: low-energy neutrons
are transported, using pointwise cross section when available
EET/TRANsmut, HADROTHErapy, NEW-DEFAults, SHIELDINg: low-energy
neutrons are transported using always multigroup cross sections
Any other SDUM value, or DEFAULTS missing: no low-energy neutron
transport
Example:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
LOW-NEUT 72.0 22.0 0.0196 2.0 1.0 11.0
* The low-energy neutron library used is the (72n, 22gamma) multigroup ENEA
* library. The user requests a printout of cross sections, kerma factors,
* probabilities, downscattering matrices and n-->gamma transfer probabilities.
* Pointwise cross sections will be used where available, and only one
* neutron per low-energy fission will be emitted, with an adjusted weight.
