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[ <--- prev -- ] [ HOME ] [ -- next ---> ] ## LOW-NEUTActivates low-energy neutron transport
WHAT(1) = number of neutron groups in the cross section set used. The FLUKA standard neutron library has 260 groups (see (10)). Default = 260 WHAT(2) = number of gamma groups No default if WHAT(1) is given, 42 otherwise. (The standard FLUKA neutron library has 42 gamma groups). WHAT(3) = maximum energy of the low-energy cross section neutron library. For the standard FLUKA neutron library, the maximum energy is 0.020 GeV. Default = 0.020 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 4.0 : In addition, information on residual nuclei is printed Default: 0.0 (minimum output) WHAT(5) = number of neutron groups to be considered thermal ones. (The standard FLUKA neutron library has 31 thermal groups). = 0, ignored < 0: resets to the default = 31.0 Default = 31.0 WHAT(6) = i0 + 10 * i1: i0 = 1: available pointwise cross sections used (see Note 4 below) and explicit and correlated 6-Li(n,t)4He, 10-B(n,alpha)7-Li, 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 Note 2). Notes: - 1) In FLUKA, transport of neutrons with energies lower than a certain threshold is performed by a multigroup algorithm. For the neutron cross section library currently used by FLUKA, this threshold is 0.020 GeV. The multigroup transport algorithm is described in Chap. (10).
- 2) 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 request LOW-NEUT, and to use PART-THRes with an energy cutoff WHAT(1) = 0.020.
- 3) 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.
- 4) Pointwise neutron transport is available, by setting WHAT(6) = 1.0 or 11.0, for the following nuclides: 1-H (above 10 eV), 6-Li (all reactions), 10-B (only for the reaction 10-B(n,alpha)7-Li). 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
- 5) The groups are numbered in DECREASING energy order (see (10) for a detailed description). The energy limits of the thermal neutron groups in the standard FLUKA neutron library neutron library are reported in 10.4.1.1}
- 6) Here are the settings for transport of low-energy neutrons corresponding to available DEFAULTS SDUM options:
CALORIMEtry, ICARUS, NEUTRONS, PRECISIOn: low-energy neutrons are transported, using pointwise cross section when available EET/TRANsmut, HADROTHErapy, NEW-DEFAults (or DEFAULTS missing), SHIELDINg: low-energy neutrons are transported using always multigroup cross sections Any other SDUM value of DEFAULTS: no low-energy neutron transport Example: *...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8 LOW-NEUT 260.0 42.0 0.020 2.0 31.0 11.0 * The low-energy neutron library used is the (260n, 42gamma) standard * multigroup 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. |

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