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Neutron transport below 14.5 MeV

Neutron transport below 14.5 MeV in the SHIELD code is simulated by the original neutron transport code LOENT (Low Energy Neutron Transport) using the 28 group neutron data system ABBN [1]. The LOENT [2] code may be used both separately and as a part of the SHIELD code. SHIELD and LOENT have common geometric module (Combinatorial Geometry) [3,4] as well as several common subroutines.

The LOENT code uses the following information from the neutron data system ABBN:

  • σt - total cross section;
  • σf - fission cross section (n,f);
  • ν - mean number of fission neutrons;
  • σc - capture cross section (n,c);
  • σin - inelastic scattering cross section (n,n'), including the reaction (n,2n);
  • σe - elastic scattering cross section (n,n);
  • μ - mean cosine of the angle of the elastic scattering;
  • σin(g,g+k) - matrix of inter group transitions at the inelastic scattering.

The LOENT code gets neutrons from an external neutron source and follows them, one by one, till the end of the neutron trajectory. The multiplication of neutrons in the reactions (n,2n) and (n,f) is possible. Each neutron has its statistical weight attached as well as the cumulative timer, which accumulates the time from the beginning of the neutron history. After transition of the neutron to thermal group, its energy does not change in the further collisions. Such neutron is transported inside the thermal group until the end of its history.

  1. L.P.Abagyan, N.O.Bazazyants, M.N.Nikolaev, A.M.Tsibulya. Group Constants for Reactor and Shielding Calculations. Energoizdat, Moscow, 1981 (in Russian).

  2. L.N.Latysheva, N.M.Sobolevsky. LOENT - the code for Monte Carlo simulation of neutron transport in complex geometries. Preprint INR RAS 1200/2008, Moscow, 2008 (in Russian).

  3. M.B.Emmet. The MORSE Monte Carlo Radiation Transport Code System, ORNL 4972 (1975).

  4. A.V.Dementyev. GEMCA-the Module for Description of Geometric Configurations. Preprint INR RAS 872/94, Moscow, 1994 (in Russian).
Contact person: Prof. Nikolai Sobolevsky, e-mail:, . (495)850 42 61
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