Study of neutron activation yields in spallation reaction of 400 MeV/u carbon on a thick lead target

The spallation-neutron yield was studied experimentally by bombarding a thick lead target with 400 MeV/u carbon beam. The data were obtained with the activation analysis method using foils of Au, Mn, Al, Fe and In. The yields of produced isotopes were deduced by analyzing the measured γ spectra of the irradiated foils. According to the isotopes yields, the spatial and energy distributions of the neutron field were discussed. The experimental results were compared with Monte Carlo simulations performed by the GEANT4+FLUKA code.     

Study of neutron spectra in a water bath from a Pb target irradiated by 250 MeV protons

Spallation neutrons were produced by the irradiation of Pb with 250 MeV protons. The Pb target was surrounded by water which was used to slow down the emitted neutrons. The moderated neutrons in the water bath were measured by using the resonance detectors of Au, Mn and In with a cadmium (Cd) cover. According to the measured activities of the foils, the neutron flux at different resonance energies were deduced and the epithermal neutron spectra were proposed. Corresponding results calculated with the Monte Carlo code MCNPX were compared with the experimental data to check the validity of the code. The comparison showed that the simulation could give a good prediction for the neutron spectra above 50 eV, while the finite thickness of the foils greatly effected the experimental data in low energy. It was also found that the resonance detectors themselves had great impact on the simulated energy spectra.     

Configuration of the valence neutrons of 17B

The reaction cross section of ¹⁷B on ¹²C target at (43.7±2.4)MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (R_rms) was deduced to be (2.92±0.10)fm, while the R_rms of the core and the valence neutron distribution are 2.28fm and 5.98fm respectively. Assuming a ``core plus 2n' structure in ¹⁷B, the mixed configuration of (2s_1/2) and (1d_5/2) of the valence neutrons is studied and the     

小角度范围内弱束缚核17F弹性散射微分截面的奇异行为

在兰州放射性束流线(RIBLL)上完成了¹⁷F/¹⁷O+²⁰⁸Pb的弹性散射微分截面角分布测量. 分析了¹⁷F/¹⁷O弹性散射产物微分截面的对数(ln(dσ/dθ))随散射角平方(θ²)的依赖关系. 结果表明, 在所测量的角度范围内(6°—20°), ¹⁷O的这一依赖关系可以用一条直线很好地拟合, 而¹⁷F的这一依赖关系需要两条不同斜率的直线才能拟合. ¹⁷F数据拟合中的这种斜率改变可能起因于¹⁷F的奇异结构. 对其他实验组数据的分析支持以上的结论, 即在一定的角度范围内, 弱束缚核与稳定核相比, 弹性散射产物微分截面的对数与散射角平方的依赖关系有明显的差异, 这可以作为深入研究“晕核”和“皮核”的一个新探针.     

高次谐波开槽回旋行波放大管自洽非线性数值模拟

 :在未考虑电子注速度零散、引导中心零散以及波导壁损耗的情况下,采用四阶龙格库塔法,对均匀截面开槽高次回旋行波放大管注波互作用进行了数值计算,得出一些重要的互作用规律。电子注绕轴作大回旋运动。在π模式、四次谐波、35.05GHz、58kV、8A、v⊥/v∥＝1.5的情况下,饱和效率达到24.4%,增益为34dB,峰值功率为113.2kW,饱和带宽为4%。     

弱束缚核17F弹性散射角分散

在兰州放射性束流线(RIBLL)上完成了¹⁷O/¹⁷F+²⁰⁸Pb的弹性散射微分截面角分布测量. 分析了¹⁷O/¹⁷F弹性散射产物的角分散, 即微分截面的对数ln(dσdθ)随散射角平方θ²的依赖关系. 结果表明, 在所测量的角度范围内(6°—20°), ¹⁷O的这一依赖关系可以用一条直线很好地拟合, 而¹⁷F的这一依赖关系需要两条不同斜率的直线才能拟合. ¹⁷F数据拟合中的这种斜率改变可能 起因于¹⁷F的奇异结构. 对其他实验组数据的分析支持以上的结论, 即在一定的角度范围内, 弱束缚核与稳定核相比, 弹性散射产物的微分截面与散射角平方的依赖关系有明显的差异, 这可以作为深入研究"晕/皮核"的一个新探针.     

基于双核模型对准裂变产物质量分布的研究

在双核模型基础上引入一维的Kramers公式，计算了⁴⁸Ca+²⁴⁴Pu，⁴⁸Ca+²³⁸U和⁵⁸Fe+²³²Th这三个反应准裂变碎片的质量分布，得到了与实验比较符合的结果.同时提取出了碎片质量分布随时间的演化关系，为理解熔合与准裂变竞争过程提供了非常有用的信息.由于准裂变在重离子熔合反应中起着重要作用，理论计算与实验结果的比较是对现有熔合模型的重要检验. 关键词： 超重元素 熔合反应 准裂变产物 质量产额     

超重复合核的存活概率

考虑角动量相关性的情况下计算了超重核259Db的裂变位垒Bf.计算了258Rf,259Db,266Hs和267Mt 4个超重核单中子蒸发的存活概率Wsur及其随角动量分波的变化关系.给出了中子蒸发宽度、裂变宽度和超重核蒸发一个中子的概率对激发能与角动量分波的依赖关系. Considering the dependence on angular momentum， the fission barriers of super heavy nuclei 259Db have been calculated. The survival probability for 258Rf， 259Db，266Hs，267Mt compound and its relation with angular momentum have been estimated. The neutron emission width， the fission width and the realization probability for one neutron emission and their relation with excitation energy and angular momentum are also presented.     

Angular Dispersion and Deflection Function for Heavy Ion Elastic Scattering

The differential cross sections for elastic scattering products of ^17F on ^208Pb have been measured. The angular dispersion plots of ln（dσ/dθ） versus θ^2 are obtained from the angular distribution of the elastic scattering differential cross sections. Systematical analysis on the angular dispersion for the available experimental data indicates that there is an angular dispersion turning angle at forward angular range within the grazing angle. This turning angle can be clarified as nucleal rainbow in classical deflection function. The exotic behaviour of the nuclear rainbow angle offers a new probe to investigate the halo and skin phenomena.     

丰中子奇异核17B的实验研究

在兰州重离子加速器国家实验室(HIRFL)放射性次级束流线(RIBLL)上,用束流透射法测量了丰中子奇异核17B与C靶反应的总截面.假定17B具有15B(核芯) 2n结构,采用Gauss HO形式的密度分布和零力程Glauber模型进行计算的结果可以很好地拟合实验数据,并得出17B的密度分布有一个很大的弥散,表明17B是双中子晕核.