| 1 | Studies on unfolding energy spectra of neutrons using maximumlikelihood expectation–maximization method显示文摘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) has 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. | Mehrdad Shahmohammadi Beni D.Krstic D.Nikezic K.N.Yu | 2019 | Nuclear Science and Techniques2019，30，9： | 2 |
| 2 | 活动星系核的γ辐射(英文)显示文摘本文第1部份,描述从SAS-2卫星得到的能量大于100MeV的宇宙Υ射线数据来证认有Υ射线的活动星系核。11个类星体、3个BLLac天体和1个射电星系的Υ射线辐射已得到证认。 本文第2部分描述活动星系核对河外Υ射线背景辐射的影响。SAS-2的Υ辐射数据,已被用来测定类星体和赛弗特星系的Υ辐射绝对光度与光学绝对光度间的函数关系,并由此导出它们对河外Υ射线背景辐射的贡献。我们指出,类星体(B<20)、赛弗特星系(1型和1.5型)对35—100MeV能量范围的弥散Υ射线背景辐射有相当大的贡献(59%)。由此我们得出河外Υ射线背景辐射可能是由类星体和赛弗特星系这类活动星系产生的结论。 本文第3部份我们对3个有Υ辐射的活动星系核综合其Υ波段和其他波段的数据,以探索这些天体辐射的发射机制。这些综合的数据对发射机制给出严格的限制。我们指出,对这3个天体的数据,与同步自康普顿模型(SSC)的预计是一致的。 | E.C.M.Young K.N.Yu | 1989 | 天文学进展1989，，3： | 0 |
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