中子俘获瞬发γ活化分析数据库

简要地介绍了热中子俘获瞬发γ射线数据的测量、评价、检验及其中子俘获瞬发γ射线活化分析数据库的研制、结构和基本数据内容等. The evaluation, measurement, and check of prompt γ-ray data for neutron capture are presented. The development of the database of prompt γ-ray activation analysis for neutron capture, and its structure and basical data are also described in the text.     

Method for measuring prompt γ-rays generated by D-T neutrons bombarding a depleted uranium spherical shell

The prompt γ-ray spectrum from depleted uranium(DU) spherical shells induced by 14 Me V D-T neutrons is measured. Monte Carlo(MC) simulation gives the largest prompt γ flux with the optimal thickness of the DU spherical shells 3–5 cm and the optimal frequency of neutron pulse 1 MHz. The method of time of flight and pulse shape coincidence with energy(DC-TOF) is proposed, and the subtraction of the background γ-rays discussed in detail. The electron recoil spectrum and time spectrum of the prompt γ-rays are obtained based on a 2 ×2 BC501 A liquid scintillator detector. The energy spectrum and time spectrum of prompt γ-rays are obtained based on an iterative unfolding method that can remove the influence of γ-rays response matrix and pulsed neutron shape.The measured time spectrum and the calculated results are roughly consistent with each other. Experimental promptγ-ray spectrum in the 0.4–3 Me V energy region agrees well with MC simulation based on the ENDF/BVI.5 library,and the discrepancies for the integral quantities of γ-rays of energy 0.4–1 Me V and 1–3 Me V are 9.2% and 1.1%,respectively.     

Maxwellian Averaged Neutron Capture Cross Sections in 56Fe and 57Fe

Measurements of the keV-neutron capture cross sections and radiative γ-ray spectrum of 56Fe and 57Fe are performed based on a 7 Li（p,n）7 Be reaction neutron source. The incident neutron spectrum on a capture sample is measured by means of a time-of-flight （TOF） method with a 6Li-glass detector. The radiative capture 7-rays emitted from an iron CS Fe or 57 Fe） or standard gold （197Au） sample are detected by a large anti-Compton NaI（TI） spectrometer covered with a heavy shield. The capture yields of samples are obtained by applying a pulse-height weighting technique to the corresponding capture γ-ray pulse-height spectrum. The Maxwellian averaged neutron capture cross sections of 56Fe and 5T Fe are derived according to the present capture cross section results.     

Observation of Rotational Bands in Neutron—Rich ^106Mo Nucleus

The rotational bands up to a spin of 16h in the neutron-rich ^106Mo nucleus have been ivestigated by measuring high-fold prompt γ-ray coincidence events following spontaneous fission of ^252Cf with a Gammasphere detector array.The ground-state band,the one-phonon and two-phonon γ-vibrational bands,as well as a quasi-particle hand have been confirmed and expanded.The other four collective rotational bands,three proposed as two-quasi-particle bands and one proposed as a β-vibrational band,have been newly observed.The characteristics of these collective bands and the possible configurations for the quasi-particle bands are discussed.     

137Eu衰变的在线测量

使用在线同位素分离器及快带传输系统研究了缺中子稀土核137Eu的衰变性质,测量了A＝137核的γ、X单谱及γ-X、γ-γ符合谱,得到了137Eu核的半衰期为9．8s,并观测到了137Eu的一条能量为209．0keV的衰变γ线． The decay properties of neutron-deficient rare earth nucleus 137Eu have been studied by means of on-line isotope separator combined with rapid tape transport system.The products were produced by 190 MeV 36Ar bombarding on Pd target via natPd (36Ar, pxn)137Eu reactions. γ, X singles and γ-X, γ-γ coincidence spectra of the nuclei with A=137 were measured. The half-life of 137Eu is obtained to be 9. 8 s. A γ-ray with energy of 209. 0 keV for 137Eu was observed.     

一个测量中子核数据的新技术——瞬发γ射线法

以测量2 3 9Pu(n ,2n)反应截面为例概述了直接测量的中子法和间接测量的瞬发γ射线法的原理及其优缺点 .阐明了瞬发γ射线法的物理内含 ,阐述了如何从测量的σm(k)约束程序中的反应机制及其参数和得到最小漏失的σm(0 ) ,并分析了σn ,2n的不确定度的来源及其贡献 .瞬发γ射线法适合不易采用直接方法的中子核数据的测量 ,具有一定的普适性 . The principles, merit and demerit of neutron and prompt γ-ray method are described through the cross section measurement for 239 Pu(n,2n) reaction. The population ways of low levels of the product nucleus are divided into a direct population from the (n,2n) reaction, a part from the upper level deexitation and a part from the all high level deexitation. The missed cross sections σ m(k) are defined. The minimum missed cross section σ m(0) that can not be measured experimentlly is obtained...     

Shape co-existence and structural evolution of the Vi13/2 band in 157Yb

The high-spin states of 157Yb have been studied via the reaction of 144Sm(16O, 3n) at 16O energy of 90 MeV using techniques of in-beam γ-ray spectroscopy. Measurement of γ-γ-t coincidences was performed with 11 BGO(AC)HPGe detectors. Based on the γ-γ coincidence relationships and the measured results of γ-ray anisotropies and DCO ratios, the level scheme for 157Yb was established. The shape co-existence and structural evolution of the Vi13/2 band with increasing angular momentum in 157Yb have been discussed. The systematics of the Vi13/2 bands in the N = 87 odd-A isotones have been compared.     

Level Structure in ^190Tl

The high-spin states of very neutron-deficient doubly odd nucleus ^190T1 have been investigated via the ^160Gd(^35C1, 5n)^190T1 reaction by using techniques of in-beam γ-ray spectroscopy. Measurements of X-γ and γ-γ-t coincidences were performed with 12BGO(AC)HPGe detectors. Based on the gated spectra, γ-γ coinci-dence relationships, γ ray energy sums, γ ray relative intensities and the previous work, the level scheme     

Halo Effect on Direct Neutron Capture Process

We calculate the capture cross sections of the ^10Be(n,γ) ^11Be reaction by means of the asymptotic normalization coefficient method and demonstrate the halo effects on the capture cross sections for the direct radiative neutron capture where a p-, s- or d-wave neutron is captured into an s-orbit or p-orbit in ^11Be by emitting an E1 γ-ray, respectively. The result shows that the enormous enhancement of the capture cross section is just due to the large overlap of the incident neutron wave with the extended tail of the ha/o, which is clearly illustrated by the reduced transition amplitude function.     

Nuclear uncertainties in the s-process simulation

The heavy elements in the Universe are formed during the s- and r-processes mainly in AGB stars and supernovae, respectively. Simulation of s- and r-nucleosynthesis critically depends on the neutron capture and weak decay rates for all the nuclei on the reaction chain. The present work analyzes systematically the neutron capture rates (cross sections) for the s-process nuclei, including ～3000 rates on ～200 nuclei. The network calculations for the constant temperature s-process have been performed using the different data sets selected as the nuclear inputs to investigate the uncertainties in the predicted s-abundances. We show that the available cross sections of neutron capture on many s-process nuclei still carry large uncertainties, which lead to low accuracy in the determination of s-process isotope abundances. We analyze the neutron capture cross section data for the same unique isobar nucleus accorded by year from previous work. Such an analysis indicates that the s-process has been studied for more than fifty years and there exist two research stages around 1976 and 2002, respectively. The needs and opportunities for future experiments and theoretical tools are highlighted to remove the existing shortcomings in the neutron capture rates.     

Monte Carlo simulation of prompt γ-ray spectra from depleted uranium under D-T neutron irradiation and electron recoil spectra in a liquid scintillator detector

To overcome the problem of inefficient computing time and unreliable results in MCNP5 calculation, a two-step method is adopted to calculate the energy deposition of prompt γ-rays in detectors for depleted uranium spherical shells under D-T neutron irradiation. In the first step, the γ-ray spectrum for energy below 7 MeV is calculated by MCNP5 code; secondly, the electron recoil spectrum in a BC501 A liquid scintillator detector is simulated based on EGSnrc Monte Carlo Code with the γ-ray spectrum from the first step as input. The comparison of calculated results with experimental ones shows that the simulations agree well with experiment in the energy region 0.4–3 MeV for the prompt γ-ray spectrum and below 4 MeVee for the electron recoil spectrum. The reliability of the two-step method in this work is validated.     

1032－A型可控中子源

本文介绍一种适用快中子与介质发生非弹散射,同时产生非弹γ射线,以及用于测量非弹γ特征能量、检测炸药和其它物质成分而研制的脉冲中子源──１０３２－Ａ型可控中子源． The study on 1032-A type controllable neutron source is described in this paper. The source can meet with inelastic scattering of fast neutron and material, generate inelastic γ-ray and measured its characteristic energy, and examined explosive material andother substance component.     

High-spin States in Odd-odd ^140Pr Nucleus

The high-spin level structures of doubly odd nucleus ^140Pr have been investigated by means of the ^130Te(^14N,4n)^140Pr reaction. The ^14N beam was obtained from the HI-13 tandem accelerator of China Institute of Atomic Energy, Beijing. The target is an enriched ^130Te metallic foil of 1.67mg/cm^2 thickness with a 10.37mg/cm^2 Pb backing. Measurements of γ-ray singles, γ-γ-t coincidences and γ-ray excitation function were performed with twelve BGO(AC)HPGe detectors. Based on detailed analysis of γ-γ coincidence relationships, γ-ray     

奇奇核90Nb的高自旋态研究

用能量为80MeV的19F束通过反应76Ge(19F,5n)90Nb布居了90Nb的高自旋态.通过在束γ测量分析90Nb退激γ射线的符合级联关系,发现了19条新的属于90Nb的γ跃迁,建立了90Nb的高自旋态能级纲图.通过经验壳模型计算指定了部分能级的组态,并结合实验DCO比值和与相邻N=49核素的系统比较,确认了新能级的自旋和宇称. The high spin states of~(90)Nb have been populated via reaction~(76)Ge(~(19)F, 5n)~(90)Nb at beam energy of 80 MeV. The de-exciting γ-rays have been measured with in-beam γ-ray spectroscopy method. After γ-γ coincidence analysis, 19 new γ transitions were identified and assigned to~(90)Nb. The new level scheme of~(90)Nb was established. Based on the semi-empirical shell model calculations, the configurations of the levels have been suggested. In addition, the spins and parities of the new levels ...     

Evaluation of the 1077 keV γ-ray emission probability from 6SGa decay

6SGa decays to the excited states of aSzn through the electron capture decay mode. New recommended values for the emission probability of 1077 keV γ-ray given by the ENSDF and DDEP databases all use data from absolute measurements. In 2011, JIANG Li-Yang deduced a new value for 1077 keV γ-ray emission probability by measuring the 69Ga（n,2n） 6SGa reaction cross section. The new value is about 20% lower than values obtained from previous absolute measurements and evaluations. In this paper, the discrepancies among the measurements and evaluations are analyzed carefully and the new values are re-recommended. Our recommended value for the emission probability of 1077 keV γ-ray is （2.72±0.16）%.     

High-spin states in neutron-rich ~(102)Mo nucleus

High-spin states in neutron-rich 102Mo nucleus have been studied by measuring the prompt γ-rays in the spontaneous fission of 252Cf. The previous level scheme has been updated and some new levels and transitions are identified. The one-phonon γ-band is expanded and a band head level of the two-phonon γ- band is proposed. The systematic characteristics of yrast bands, one-phonon γ-bands, two-phonon γ-bands and quasi-particle bands in 102Mo, 104Mo and 106Mo are discussed.     

短寿命核转轮传送装置

在中国原子能科学研究院的串列式静电加速器上建立了传送短寿命核的转轮装置,可用于鉴别和研究寿命短至几秒的核素．该装置已用于新的缺中子核素９０Ｒｕ的鉴别及其半衰期和衰变γ的测量． A wheel device for transporting short-lived nuclei has been constructed at the HI-13 tandem accelerator of CIAE. The device can be used in the identification and investigation of nuclides with life-times as short as a few seconds. With the aid of this device a new nutron-deficient nuclide 90Ru has been identified. Its half-life and decay γ-rays have been measured.     

A Monte Carlo simulation and setup optimization of output ef f iciency to PGNAA thermal neutron using ~(252)Cf neutrons

We present the design and optimization of a prompt γ-ray neutron activation analysis(PGNAA) thermal neutron output setup based on Monte Carlo simulations using MCNP5 computer code. In these simulations, the moderator materials, reflective materials, and structure of the PGNAA252 Cf neutrons of thermal neutron output setup are optimized. The simulation results reveal that the thin layer paraffin and the thick layer of heavy water moderating effect work best for the252 Cf neutron spectrum. Our new design shows a significantly improved performance of the thermal neutron flux and flux rate, that are increased by 3.02 times and 3.27 times, respectively,compared with the conventional neutron source design.     

New multi-phonon gamma vibrational bands in A～110 neutron-rich nuclei

The high spin states of neutron-rich 103Nb, 107Tc and 109Tc nuclei in A~110 region have been investigated by measuring prompt γ-γ-γ coincident measurements populated with the spontaneous fission of 252Cf with the Gammasphere detector array. In 103Nb, one-phonon K = 9/2 and two-phonon K = 13/2 γ-vibrational bands have been identified. In 107Tc and 109Tc, one-phonon K = 11/2 and two-phonon K = 15/2 γ-vibrational bands, in which the zero-phonon bands are based on K=7/2 excited states, have also been identified...     

Calculation of prompt fission neutron spectrum for 233U（n,f） reaction by the semi-empirical method

The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the nth＋233U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.