核反应总截面和奇异结构研究

本文总结了晕和皮等奇异核子结构研究的现状 ,介绍了发现晕和皮现象的实验证据。然后集中介绍了利用奇异核反应总截面的实验测量和理论模型 ,从中提取奇异核物质半径、核内核子分布以及介质中的核子 核子碰撞截面等重要信息 ,我们将特别强调通过实验测量和理论模型之间的联系来研究奇异结构性质。     

Scaling of anisotropic flows and nuclear equation of state in intermediate energy heavy ion collisions

Elliptic flow ($v_2$) and hexadecupole flow ($v_4$) of light clusters have been studied in detail for 25 MeV/nucleon $^{86}$Kr + $^{124}$Sn at large impact parameters by using a quantum molecular dynamics model with different potential parameters. Four sets of parameters including soft or hard equation of state (EOS) with or without symmetry energy term are used. Both number-of-nucleon ($A$) scaling of the elliptic flow versus transverse momentum ($p_{\rm t}$) and the scaling of $v_4/A^{2}$ versus $(p_{\rm t}/A)^2$ have been demonstrated for the light clusters in all above calculation conditions. It is also found that the ratio of $v_4/{v_2}^2$ maintains a constant of 1/2 which is independent of $p_{\rm t}$ for all the light fragments. Comparisons among different combinations of the EOS and the symmetry potential term show that the above scaling behaviours are sound and independent of the details of potential, while the strengths of flows are sensitive to the EOS and the symmetry potential term.     

“颈”发射过程中的中等质量碎片的研究

系统地研究“颈”发射过程中的中等质量碎片,能使我们更好地理解中能核反应的动力学和热力学性质.采用具有不同的同位旋靶核研究了靶同位旋与中等质量碎片的关系,以及区分反应过程中类弹、类靶产生的中等质量碎片和“颈”发射过程中产生的中等质量碎片.HJ4/9] By systematic study of the IMF produced the “neck”emission process, one can understand much better about the dynamics and thermodymanics of the intermediate energy nuclear reaction. The isospin dependence of IMF emission was studied for the reaction system with different isospin target nucleus and the different IMF production mechanisms that originate from projectile like、 target like and the “neck” were distinguished.     

上海激光电子γ源

激光具有高强度、 高极化度等优异的性能。 用激光束轰击高能电子束就可以产生高强度、 高极化度的γ射线束。 上海激光电子γ源就是上海同步辐射装置上的这样一条束线站。 预计可以获得能量范围为1—22 MeV的准单色、 高强度（109—1011 s-1）和高极化度（线极化或圆极化）的γ射线束。 介绍了这条束线站目前的进展情况。 Shanghai Laser Electron Gamma Source (SLEGS) is a high intensity,short pulse and compact γ ray source which is based on inverse Compton scattering via interaction between pulsed high power laser beams and picosecond relativistic electron bunches. One of the attractive features of the laser Compton scattering is the easy control of polarization of the produced high energy photons that duplicates polarization of the applied laser beam. The γ ray with energy up to 22 MeV and intensity of 109—1011s 1 are expected to be produced by Compton backscattering of CO2 laser photons on the 3.5 GeV electrons bunches in the Shanghai Synchrotron Radiation Facility (SSRF). In this communication, we report same simulation results and the progressing status of SLEGS.     

Phenomenological Scaling of Rapidity Dependence for Anisotropic Flows in 25 MeV/nucleon Ca＋Ca by Quantum Molecular Dynamics Model

Anisotropic flows （v1, v2, v3 and v4） of light fragments up to the mass number 4 as a function of rapidity are studied for 25 MeV/nucleon ^40Ca ＋ ^40Ca at large impact parameters by a quantum molecular dynamics model. A phenomenological scaling behaviour of rapidity dependent flow parameters vn （n = 1, 2, 3 and 4） is found as a function of mass number plus a constant term, which may arise from the interplay of collective and random motions. In addition, v4/v2^2 keeps to be almost independent of rapidity and remains a rough constant of 1/2 for all light fragments.     

用修正的擦碎模型研究碎裂反应的同位素分布

对统计擦碎模型(SAA)的计算方法进行修正和优化,并引入参数化的介质中核子-核子碰撞截面和核物质密度分布弥散度,可很好符合从中能到高能下碎裂反应产生同位素分布的实验截面,并能计算和拟合远离峰位、很低截面的同位素分布.     

弹核碎裂反应中同位旋效应的系统研究

用统计擦碎模型对中能区不同弹靶体系在弹核碎裂反应中的同位旋效应和同位旋标度率现象进行了系统研究. 发现归一的同位素分布峰位差和约化的同位旋标度率参数随(Z_proj－Z)/Z_proj or (N_proj－N)/N_proj呈指数下降, 与反应系统大小无关. 指出约化的同位旋标度率参数可以用来研究中能重离子碰撞中反应系统的激发程度和非对称核物质的状态方程.     

Determination of the stellar reaction rate for 12C（α,γ）16O： using a new expression with the reaction mechanism

The astrophysical reaction rate of 12C(α, γ)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9=0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(α, γ)16O reaction rates are calculated in the temperature range from T9=0.3 to 2 according to all the available cross section data. A new analytic expression of the 12 C(α, γ)16 O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3σ fit errors, are obtained from fit to our calculated reaction rate from T9=0.3 to 2. Using the fit results, the analytic expression of 12C(α, γ)16O reaction rate is extrapolated down to T9=0.05 based on the underlying physics. The 12C(α, γ)16 O reaction rate at T9=0.2 is (8.78 ± 1.52) × 1015 cm3s-1mol-1. Some comparisons and discussions about our new 12 C(α, γ)16 O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9=2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(α, γ)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(α, γ)16O reaction rates.     

Measurement of 232Th (n,γ) cross section at the CSNS Back-n facility in the unresolved resonance region from 4 keV to 100 keV

The neutron capture cross section of ²³²Th was measured at the neutron time-of-flight facility Back-n of China Spallation Neutron Source (CSNS) for the first time. The measurement was performed with 4 hydrogen-free deuterated benzene C₆D₆ liquid scintillation detectors, in the ES#2 experiment station on the beam line, at a distance of about 76 m from the neutron-production assembly. The total energy detection principle in combination with the pulse height weighting technique (PHWT) was applied to analyze the measured data. Results of the ²³²Th (n,γ) reaction cross section in the unresolved resonance region from 4 keV to 100 keV were obtained, which shows a good agreement with the existing experimental data from EXFOR, as well as with the evaluated data from the ENDF/B-VIII.0 and CENDL-3.1. In addition, the excitation function of ²³²Th (n,γ)²³³Th reaction in the unresolved resonance region was theoretically calculated by using the code TALYS-1.95. By fitting the experimental cross section and theoretical data, the average parameters in the unresolved resonance region were extracted. The datasets are openly available at http://dx.doi.org/10.11922/sciencedb.j00113.00015.     

Studies on the exotic structure of 23Al

The longitudinal momentum distribution (P_//) of fragments after one-proton removal from ²³Al and reaction cross sections (σ_R) for ^23,24Al on carbon target at 74A MeV have been measured simultaneously. An enhancement in σ_R is observed for ²³Al compared with ²⁴Al. The full width at half maximum of the P_// distribution for ²²Mg fragments has been determined to be 232±28 MeV/c. Analysis of P_// using the Few-Body Glauber Model indicates a dominant d-wave configuration for the valence proton in the ground state of ²³Al. The exotic structure in ²³Al is discussed.