The effects of shielding around the source on neutron energy spectra |
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Authors: | B Pehlivanovic P Marinkovic S Avdic |
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Institution: | 1. Faculty of Educational Science , University of Bihac , Bosnia and Herzegovinamarinkovic@etf.rs;3. Faculty of Electrical Engineering , University of Belgrade , Belgrade, Serbia;4. Department of Physics, Faculty of Science , University of Tuzla , Bosnia and Herzegovina |
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Abstract: | The knowledge of neutron energy spectra contributes to unambiguous identification of neutron sources in the fields of nuclear safeguards and nuclear non-proliferation. Since a real scenario situation includes the presence of shielding around the source, we have investigated the influence of the potential shielding surrounding the source on the shape of energy spectra for a few neutron sources. We have applied the maximum-likelihood, expectation–maximisation (MLEM) method with one-step-late (OSL) algorithm for neutron spectra unfolding. The pulse height distributions used in the unfolding procedures were simulated with the high accuracy by using the MCNP-PoliMi code based on the Monte Carlo method. A possibility to identify the shielded neutron sources by using the unfolding method was examined with two continuous-in-energy sources, such as 252Cf and 241Am–Be in source-shielding configurations with lead (Pb) and polyethylene (PE) blocks. The results of calculations have shown that the identification of 252Cf and 241Am–Be sources with 2.5 cm of Pb and PE shield can be achieved successfully by using the MLEM method with the OSL algorithm. However, the unfolded results for 252Cf and 241Am–Be sources with 10 cm of PE shield significantly deviate from the reference spectra and the sources cannot be correctly identified on the basis of their unfolded energy spectra. |
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Keywords: | shielded neutron source unfolding procedure pulse height distribution neutron energy distribution maximum-likelihood method Monte Carlo method |
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