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10} Low-energy neutrons in FLUKA

Low-energy neutron transport is activated by option LOW-NEUT, but it is requested by defaults with most of the options available with the DEFAULTS command (CALORIMEtry, EET/TRANsmut, HADROTHErapy, ICARUS, NEUTRONS, NEW-DEFAults, PRECISIOn, SHIELDINg). The only exception is the DEFAULTS option EM-CASCAde. However, command LOW-NEUT may be still necessary in order to give information about the cross section library used, or to issue special requests. The FLUKA traditional way for neutron transport below 20 MeV is a multi-group approach, which is fast, compact, and very reliable. It is particularly suited for shielding problems. This approach is inherently inclusive and it does not preserve correlations. Energy and momentum are conserved on average. However for some problems where the fine structure of the cross sections (resonances) must be explicitly treated, and/or correlations among products are important, the multigroup approach cannot be used. Starting with FLUKA2021.2 an alternative approach based on fully correlated continuous (pointwise) cross sections is available.

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