Simulation of radionuclide neutron sources with Monte Carlo codes

Auditorium B. Touschek (Laboratori Nazionali di Frascati, Via Enrico Fermi 40, Frascati)

Auditorium B. Touschek

Laboratori Nazionali di Frascati, Via Enrico Fermi 40, Frascati

Via Enrico Fermi 40 00044 Frascati

In the ISO Standard 8529 series, "Reference neutron radiations", the reference 241AmBe spectrum is based on the Kluge and Weise publication (Radiat. Prot. Dosim. 2, 85-93 (1982). The presented tabulated data are valid for 1) "small" sources with "light" encapsulation, 2) neutron energy above 0.11 MeV 3) neutron spectrum outside the source.
For many applications (calibration of radiation protection dosimetry devices), this energy distribution is used independently of the source size. In order to take some account of the spectral alterations resulting from the sources characteristics (size, mixture density, encapsulation) the ISO spectrum may be considered as a "primary" spectrum, isotropically emitted at each site in the radioactive material. Then the (241AmBe) emitted spectrum can be derived from transport calculations of that "primary" spectrum through the source assembly.
Two other approaches may be applied: either inferring the primary spectrum by a recursive calculation (NPL method) or calculating a primary spectrum by starting from the (a,n) reaction kinetics as done by Geiger and Van der Zwan (NIM 131, 315-321 (1975).
Some new results, derived from the second method that takes into account a modelling of the AmO2 cluster size, are presented. Two series of results were obtained by using the following codes: 1) SOURCES-4C / -5A by E.F. Shores (LANL) distributed by NEA Data Bank; 2) a home-made code kindly distributed by Norio Tsujimora (Tokai RDC -JAEN).
These simulations are intended to provide new data for the incoming revision of the ISO Standard 8529-1 within the working group TC85 / SC2 / WG2 “Reference Radiation fields”.

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