Mehrdad Shahmohammadi Beni, D. Krstic, D. Nikezic, et al. Studies on unfolding energy spectra of neutrons using maximum-likelihood expectation-maximization method. [J]. Nuclear Science and Techniques 30(9):134(2019)
Mehrdad Shahmohammadi Beni, D. Krstic, D. Nikezic, et al. Studies on unfolding energy spectra of neutrons using maximum-likelihood expectation-maximization method. [J]. Nuclear Science and Techniques 30(9):134(2019) DOI： 10.1007/s41365-019-0662-7.
Studies on unfolding energy spectra of neutrons using maximum-likelihood expectation-maximization method
Energy spectra of neutrons are important for identification of unknown neutron sources and for determination of the equivalent dose. Although standard energy spectra of neutrons are available in some situations, e.g., for some radiotherapy treatment machines, they are unknown in other cases, e.g., for photoneutrons created in radiotherapy rooms and neutrons generated in nuclear reactors. In situations where neutron energy spectra need to be determined, unfolding the required neutron energy spectra using the Bonner Sphere Spectrometer (BSS) and Nested Neutron Spectrometer (NNS) have been found promising. However, without any prior knowledge on the spectra, the unfolding process has remained a tedious task. In this work, a standalone numerical tool named "NRUunfold" was developed which could satisfactorily unfold neutron spectra for BSS or NNS, or any other systems using similar detection methodology. A generic and versatile algorithm based on maximum-likelihood expectation-maximization method was developed and benchmarked against the widely used STAY’SL algorithm which was based on the least squares method. The present method could output decent results in the absence of precisely calculated initial guess, although it was also remarked that employment of exceptionally bizarre initial spectra could lead to some unreasonable output spectra. The neutron count rates computed using the manufacturer’s response functions were used for sensitivity studies. The present NRUunfold code could be useful for neutron energy spectrum unfolding for BSS or NNS applications in the absence of a precisely calculated initial guess.
J. Chadwick, The existence of a neutron. Proc. R. Soc. Lond. A 136, 692-708 (1932).
N. Feather, The collisions of neutrons with nitrogen nuclei. Proc. R. Soc. Lond. A 136, 709-727 (1932). DOI: 10.1098/rspa.1932.0113http://doi.org/10.1098/rspa.1932.0113
B. Maglich, Adventures in experimental physics, (World Science Education, Princeton, 1972).
F.D. Brooks, H. Klein, Neutron spectrometry—historical review and present status. Nucl. Instr. Meth. Phys. Res. A 476, 1-11 (2002). DOI: 10.1016/S0168-9002(01)01378-Xhttp://doi.org/10.1016/S0168-9002(01)01378-X
R.L. Bramblett, R.I. Ewing, T.W. Bonner, A new type of neutron spectrometer. Nucl. Instr. Meth. 9, 1-12 (1960). DOI: 10.1016/0029-554X(60)90043-4http://doi.org/10.1016/0029-554X(60)90043-4
R. Maglieri, A. Licea, M. Evans, et al., Measuring neutron spectra in radiotherapy using the nested neutron spectrometer. Med. Phys. 42, 6162-6169 (2015). DOI: 10.1118/1.4931963http://doi.org/10.1118/1.4931963
J. Dubeau, S.S. Hakmana Witharana, J. Atanackovic et al. A neutron spectrometer using nested moderators. Radiat. Prot. Dosim. 150, 217-222 (2011). DOI: 10.1093/rpd/ncr381http://doi.org/10.1093/rpd/ncr381
F.G. Perey, Least-squares dosimetry unfolding: The program STAY'SL, (Oak Ridge National Laboratory/TM-6062, 1977).
R. Maglieri, A study of photoneutron spectra around high-energy medical linear accelerators using Monte Carlo simulations and measurements, (McGill University, Quebec, 2014).
G.J. Jacobs, H. Liskien, Energy spectra of neutrons produced by α-particles in thick targets of light elements. Ann. Nucl. Energy 10, 541-552 (1983). DOI: 10.1016/0306-4549(83)90003-8http://doi.org/10.1016/0306-4549(83)90003-8
S.I. Ahmad, N. Ahmad, Aslam, Effect of new cross-section evaluations on criticality and neutron energy spectrum of a typical material test research reactor. Ann. Nucl. Energy 31, 1867-1881 (2004). DOI: 10.1016/j.anucene.2004.06.005http://doi.org/10.1016/j.anucene.2004.06.005