New detector system to measure (n,γ) reaction cross section precisely in China

Based on the urgent requirement of the (n,γ) reaction cross-section in the energy range of keV~MeV, 4π gamma total absorption facility (GTAF) is being constructed at China Institute of Atomic Energy (CIAE). In this paper, firstly the review of historic experimental facilities over the world is presented, and then measurement method of GTAF is described. Finally, the structure requirement for GTAF is presented. Neutron capture reactions are the key process of nucleosynthesis in astrophysics beyond iron element. The application of such facility will improve the experimental condition for the research of (n,γ) reaction.     

中子引起氘核破裂反应的实验研究

对25 MeV中子引起氘核破裂反应的中子-中子准自由散射和17.36 MeV中子引起氘核破裂反应的中子-中子末态相互作用进行了细致的研究。首先,以小于5%的不确定度,精确测量了25MeV中子-中子准自由散射出射的中子三重微分截面。实验数据用基于现实核子-核子势(CD-Bonn,Argonne!18,Nijm I和II)的理论计算配合Monte-Carlo模拟进行了分析。实验结果比基于CD-Bonn势的理论预言高(16.0±4.6)%,进一步证实了目前的理论在中子-中子准自由散射方面还无法准确描述实验数据。其次,通过运动学非完全测量,精确测量了17.36 MeV中子引起氘核破裂反应在0°角附近出射的质子能谱,用基于现实核子-核子势(CD-Bonn、Bonn-B和Nijm I)的理论计算以及Monte-Carlo模拟分析了所测得的质子能谱,确定了中子-中子散射长度ann=(-16.8±0.6)fm。     

Measurement of the neutron spectrum of a Pu-C source with a liquid scintillator

The neutron response function for a BC501A liquid scintillator （LS） has been measured using a series of monoenergetic neutrons produced by the p-T reaction. The proton energies were chosen such as to produce neutrons in the energy range of 1 to 20 MeV. The principles of the technique of unfolding a neutron energy spectrum by using the measured neutron response function and the measured Pulse Height （PH） spectrum is briefly described. The PH spectrum of neutrons from the Pu-C source, which will be used for the calibration of the reactor antineutrino detectors for the Daya Bay neutrino experiment, was measured and analyzed to get the neutron energy spectrum. Simultaneously the neutron energy spectrum of an Am-Be source was measured and compared with other measurements as a check of the result for the Pu-C source. Finally, an error analysis and a discussion of the results are given.     

Measurement of the response function and the detection effciency of an organic liquid scintillator for neutrons between 1 and 30 MeV

The light output function of a φ50.8 mm×50.8 mm BC501A scintillation detector was measured in the neutron energy region of 1 to 30 MeV by fitting the pulse height （PH） spectra for neutrons with the simulations from the NRESP code at the edge range. Using the new light output function, the neutron detection effciency was determined with two Monte-Carlo codes, NEFF and SCINFUL. The calculated effciency was corrected by comparing the simulated PH spectra with the measured ones. The determined effciency was verified at the near threshold region and normalized with a Proton-Recoil-Telescope （PRT） at the 8-14 MeV energy region.     

15N（p,n)15O反应中子源0°角激发函数测量

利用中国原子能科学研究院HI-13串列加速器上的多探测器快中子飞行时间谱仪, 测量了38个不同入射质子能量点下15N（p, n)15O反应0°角方向的激发函数。 测量数据用蒙特卡罗方法进行了模拟, 以进行中子注量衰减和入射窗厚度的不确定度修正。 实验在入射质子能量位于6.029—8.056 MeV之间时发现了3个共振峰, 这一点与DROSG 2000评价数据及PTB数据相符合, 但三家的截面数值存在差异, 对这些差异需要作进一步深入探讨。 The excitation function of 15N（p, n)15O reaction at 0 degree was measured at 38 energy points using the fast neutron Time of Flight (TOF) spectrometer at the HI 13 Tandem Accelerator in the China Institute of Atomic Energy（CIAE）. The measured data were analyzed by Monte Carlo simulation for the corrections of neutron flux attenuation and uncertainty of the thickness of the entrance foil. Three resonance peaks were observed in this experiment in the energy range from 6.029 to 8.056 MeV,which is comparable with the DROSG 2000 evaluated data and the PTB data. However,more experimental studies are needed since the cross sections deviate with each other.     

中子与9Be和6,7Li反应的次级中子发射谱实验研究

测量了8.17MeV与10.27MeV中子与⁹Be和^6,7Li作用的次级中子双微分截面. 对于10.27MeV, 为了消除从D(d,np)破裂反应来的源破裂中子对双微分截面测量结果的影响, 采用了常规多探测器快中子飞行时间谱仪和非常规多探测器快中子飞行时间谱仪相结合的办法. 用Monte-Carlo方法对实验测量得到的飞行时间谱进行了详细的模拟, 通过测量谱与模拟谱的比较, 得到了实验测量的次级中子双微分截面. 实验测量结果以n-p(常规谱仪)和n-C(非常规谱仪)弹性散射微分截面作为归一. 测量结果与评价数据以及其他测量数据进行了比较. 用一个基于Hauser-Feshbach和激子模型的轻核核反应理论模型对^6,7Li的次级中子双微分截面进行了计算, 理论计算结果与实验结果符合得较好.     

中子引起氘核破裂反应的实验研究

对25 MeV中子引起氘核破裂反应的中子-中子准自由散射和17.36 MeV中子引起氘核破裂反应的中子-中子末态相互作用进行了细致的研究。首先,以小于5%的不确定度,精确测量了25MeV中子-中子准自由散射出射的中子三重微分截面。实验数据用基于现实核子-核子势（CD-Bonn,Argonne!18,Nijm I和II）的理论计算配合Monte-Carlo模拟进行了分析。实验结果比基于CD-Bonn势的理论预言高（16.0±4.6）%,进一步证实了目前的理论在中子-中子准自由散射方面还无法准确描述实验数据。其次,通过运动学非完全测量,精确测量了17.36 MeV中子引起氘核破裂反应在0°角附近出射的质子能谱,用基于现实核子-核子势（CD-Bonn、Bonn-B和Nijm I）的理论计算以及Monte-Carlo模拟分析了所测得的质子能谱,确定了中子-中子散射长度ann=（-16.8±0.6）fm。