晕核6He（25 MeV/u）的单、双中子转移截面测量

实验测量了25 MeV/u 的6He+9Be反应中的单、双中子转移微分截面. 利用反应耦合道模型初步分析了实验数据, 计算大体重现截面值. 转移反应对末态有相当的选择性, 并且双中子转移截面主要来自到基态的一步过程. 后角度截面的上升可能与连续态的耦合有关. Differential cross sections for quasi elastic scattering at forward angles and for 1n and 2n transfer reaction at backward angles induced by 6He at 25 MeV/u from 9Be target were measured. The experimental data were analyzed in the framework of the CRC model. The raise at backward angle of the 1n and 2n transfer cross section can not reproduced by the current calculation.     

Measurement of One— and Two—Neutron Transfers in Reaction of ^6He＋^9Be at 25MeV／u

The cross sections one-and two-neutron transfers induced by 6He at 25MeV/u on a^9Be target were measured in RIKEN.Clear identification of the recoiled Be isotopes was achieved.In total five 11Be and 371 ^10Be events,the corresponding two-and one-neutron transfers were obtained and analysed for transfer reaction cross sections.The results are useful to determine the spectroscopic factors of the internal halo structure of the 6He nucleus.     

Measurement of the Breakup Cross Sections in ^6He＋^9Be Reaction at 25 MeV／Nucleon

The breakup reaction cross sections were measured for the reaction of^6He at 25 MeV/nucleon from ^9Be target with intensity of 10^5 pps. By fitting the energy spectra of breakup α particles with Gaussian functions, the angular distribution of differential cross sections in the laboratory system has been extracted and compared with the Serber model calculations. The good agreement between the calculation and the experimental data favours a dominant configuration of the ^4He core plus valence neutrons for the structure of^6He.     

晕核6He(25 MeV/u)在9Be上的弹性散射研究

分析了北京大学核物理实验小组在日本RIKEN实验室完成的25 MeV/u 6He和9Be的弹性散射实验数据，得到了弹性散射微分截面角分布. 利用双折叠模型，并通过拟合弹性散射微分截面得到了此弹靶体系在此能量下的弹性散射光学势. We analyzed the 6He elastic scattering from 9Be target at 25 MeV/u. A Center of Beam (CB) method was used to calibrate the particle tracking detectors and set the reference system of the detection system. The double folding model approach was used to calculate the real part of the optical model potential. The preliminary optical model potential parameters were extracted by fitting the experimental differential elastic scattering cross sections.     

质子滴线区新核素25P的鉴别

在兰州放射性束流装置RIBLL上 ,利用磁刚度B_ρ、飞行时间t_TOF和多重望远镜ΔE- E联合探测方法测量了69Me V/u 36Ar轰击Be靶产生的 P同位素碎片的同位素分布,并与 EPAX经验公式的计算结果进行了比较 ,在质子滴线区首次鉴别出了新核素25PThe mass distribution of the phosphor fragments induced by projectile fragmentation reaction of 69 MeV/u 36Ar + 9Be was measured at the projectile fragment separator RIBLL at IMP. The fragment products were identified by determining the magnetic rigidity Bρ , the time of flight t_TOF and their energy loss ΔE . The experimental isotope distribution was compared to the result of the empirical parameterization EPAX. Three events for the new nuclide 25P in the...     

丰中子核6He在28Si靶上的反应总截面测量

实验测量了20—40MeV u的轻丰中子核6He在Si靶上的反应总截面,并且结合6He的高能实验数据,采用双参数HO密度分布形式用Glauber模型计算得到较好的拟合.与Warner的实验数据比较,反应总截面数据系统性好,并与能量有明显的依赖关系. Total reaction cross section (σt) was measured for neuton rich nuclei 6He on 28Si target from about 20 to 40 MeV/u and compared with Warner s experimental data. It is found that the total cross section of 6He on 28Si depends on the energy and it can be fitted well by Glauber model using two term HO density distribution from high energy data of 6He.     

Single-Proton Pickup Reaction of the Halo Nucleus ^6He on a ^9Be Target at 25 MeV/nucleon

The inclusive differential cross sections of the ^7 Li nucleus in a reaction induced by ^6He on a ^9Be target are measured at an incident energy of 25 MeV/nucleon. Finite-range distorted-wave Born approximation calculations suggest that these ^7 Li particles are formed in a direct single-proton pickup reaction ^9Be（^6He,^7 Li）^8Li. The experimental data can be well reproduced by taking into account of the contributions of both the ground states and the first excited states of ^7Li and ^8Li.     

8.19 MeV中子与9Be作用的次级中子双微分截面测量

用中国原子能科学研究院HI13串列加速器上的多探测器快中子飞行时间谱仪, 测量了8.19 MeV中子与9Be作用时, 从20°到160°区间26个角度的次级中子双微分截面。测量截面以np散射截面作为标准进行归一。实验结果用Monte Carlo方法进行了中子注量率衰减、多次散射和有限几何修正, 并用MCNP4C程序对所用的Monte Carlo程序进行了验证。测量结果与评价数据以及其它实验室的数据进行了比较。The secondary neutron emission double differential cross section of 9Be induced by 8.19 MeV neutron was measured at 26 different angles from 20°to 150°by using the multi detector fast neutron TOF spectrometer at the HI 13 Tandem Accelerator at China Institute of Atomic Energy(CIAE). The results were normalized to np scattering measurement. A special Monte Carlo code which was validated with the MCNP 4C code was employed to analyze the measured data for the corrections of neutron flux attenuation, multiple scattering and finite geometry. The measured results were compared with the evaluated data and the other measurements.      

碳离子肿瘤治疗中弹核碎裂反应测量系统的研制

为了评估弹核碎裂反应在碳离子肿瘤治疗中产生的影响,中国科学院近代物理研究所建立了一套探测器系统用来测量相关反应产物。这套探测系统包括起始探测器、水靶系统、带电粒子鉴别系统和中子测量系统。利用中国科学院近代物理研究所250 MeV/u 12C6+ 束打50 mm水靶的实验在束测试了这套系统的性能。实验结果表明,通过ΔE-E 和TOF-ΔE 两种粒子鉴别方法这套探测系统清楚地区分了H,He,Li,Be,B和C 等元素。通过计算不同Z 值带电碎片的微分截面得到了这些带电碎片(本工作给出元素H 和He)相应的角分布。这套探测系统中的带电粒子测量系统性能达到了设计的预期目标。For estimating the influence of the projectile breakup reaction on carbon ion tumour therapy, a detector system was built by IMP(Institute of Modern Physics), Chinese Academy of Sciences(CAS), and used to detect the results of the reaction. The system is composed of start detector, water target system, charged fragments detector system and neutron detector system. The performance of the detector system was tested in the experiment of 5 cm thick water target bombarded by 250 MeV/u carbon beam. The results reveal that the charged fragments, such as elements H, He, Li, Be, B and C, were identified clearly by ΔE-E and ΔE-TOF techniques. The angular distributions of some charged fragments were obtained by calculating the charge-changing cross-sections of the fragments(e.g. elements H and He isotopes in our work). The test results prove that the charged fragment detector system achieves the design aim.     

轻核(n,x)反应微分截面的实验测量

对本课题组十几年来的(n,x)反应实验研究工作进行了评述.介绍了屏栅电离室的特点、构造与工作原理.用屏栅电离室在北京大学4.5MV静电加速器上测量了1—7MeV中子6Li(n,t)4He和10B(n,α)7Li反应的微分截面与截面,对实验结果进行了讨论. Our research work on (n, x) reaction for more than one decade is reviewed. The characteristics, structure, and working principle of the gridded ionization chamber are discussed. Differential cross sections and cross sections of the~(6)Li(n, t)~(4)He and~(10)B(n, α)~(7)Li reactions were measured in the neutron energy range of 1—7 MeV by using the GIC method. Experiments were carried out at the 4.5 MV Van de Graaff accelerator of Peking University. Results of the measurement are discussed.     

A Common Optical Potential for ~4He+~(12)C at Intermediate Energies

A common optical potential for ~4He+~(12)C at intermediate bombarding energies,which is essential in analyzing exotic nuclei with ~4He clusters,is obtained based on the Sao Paulo potential.Among systematic optical potentials for ~4He+~(12)C,this potential has the merit of using a fixed imaginary part of the Woods-Saxon form.By opticalmodel calculations,this potential reproduces the experimental elastic scattering angular distributions of ~4He+~(12)C well within the energy range of 26A-60 A MeV.It is also applied successfully in calculations of the breakup reactions of ~6Li+~(12)C and ~6He+~(12)C with a three-body continuum discretized coupled-channel method.     

Measurement of the ~2H(~7Be,~6Li)~3He reaction rate and its contribution to the primordial lithium abundance

In the standard Big Bang nucleosynthesis(SBBN) model, the lithium puzzle has attracted intense interest over the past few decades, but still has not been solved. Conventionally, the approach is to include more reactions flowing into or out of lithium, and study the potential effects of those reactions which were not previously considered.~7Be(d,~3He)~6Li is a reaction that not only produces~6Li but also destroys~7Be, which decays to~7Li, thereby affecting~7Li indirectly. Therefore, this reaction could alleviate the lithium discrepancy if its reaction rate is sufficiently high.However, there is not much information available about the~7Be(d,~3He)~6Li reaction rate. In this work, the angular distributions of the~7Be(d,~3He)~6Li reaction are measured at the center of mass energies Ecm = 4.0 Me V and 6.~7Me V with secondary~7Be beams for the first time. The excitation function of the~7Be(d,~3He)~6Li reaction is first calculated with the computer code TALYS and then normalized to the experimental data, then its reaction rate is deduced. A SBBN network calculation is performed to investigate its influence on the~6Li and~7Li abundances. The results show that the~7Be(d,~3He)~6Li reaction has a minimal effect on~6Li and~7Li because of its small reaction rate. Therefore,the~7Be(d,~3He)~6Li reaction is ruled out by this experiment as a means of alleviating the lithium discrepancy.     

Atomic structure of the Zr–He,Zr–vac,and Zr–vac–He systems: First-principles calculation

The ab initio investigations have been performed for the atomic structure of the Zr–He, Zr–vac, and Zr–vac–He systems with concentrations of helium atoms and vacancies (vac) of ~6 at %. A heliuminduced instability of the zirconia lattice has been revealed in the Zr–He system, which disappears with the formation of vacancies. The most preferred positions of impurities in the metal lattice have been determined. The energy of helium dissolution and the excess volume introduced by helium have been calculated. It has been established that the presence of helium in the Zr lattice leads to a significant decrease in the energy of vacancy formation.     

厚靶D（d,n）^3He反应加速器中子源的产额、能谱和角分布

给出一种计算氘钛厚靶D(d,n)3He反应加速器中子源的产额、能谱和角分布的方法,并发展了一个计算机模拟程序,程序能够计算氘束流能量小于1.0 MeV的中子源的产额、能谱和角分布.计算时使用推荐的D(d,n)3He反应截面数据和来自SRIM-2003程序的氘在氘钛靶中的阻止本领数据.给出一些典型计算结果,包括中子积分产额、中子能谱和角分布.     

氦同位素与氢分子碰撞的振转激发分波截面研究

用密耦近似方法和Tang-Toennies势模型计算了E=0·7eV时,氦原子的四种同位素3He,4He,9He,10He与氢分子H2碰撞体系的振转激发分波截面.通过分析各碰撞体系分波截面的差异,探讨了He(3He,4He,9He,10He)-H2碰撞体系的弹性碰撞、纯转动激发和振转激发情况下,其分波截面随量子数和体系约化质量的变化规律.     

Study of ~3He inelastic scattering on ~(13)C and ~(14)C at 37.9 MeV

The differential cross sections of elastic and inelastic scattering of ³He ions on ¹³C and ¹⁴C have been studied at an energy of 37.9 MeV with a double folding model based on M3Y-Reid effective nucleon-nucleon interaction. The resulted parameters have been used for the standard Distorted Wave Born Approximation calculations of angular distributions corresponding to different excitations levels of ¹³C and ¹⁴C and deformation parameters have been deduced.     

25MeV/u 6He在9Be靶上的弹性转移反应研究

报告了25MeV/u ⁶He在⁹Be靶上的弹性散射和弹性转移的实验结果. 用光学模型和一阶DWBA的方法计算了弹性散射和³He集团转移的截面, 计算结果和实验测量基本一致. 计算表明³He在⁹Be中的谱幅度应该明显大于壳模型的理论计算值0.70.     

非束缚核9He的实验研究

简要介绍了目前有关非稳定核^9He的实验和理论研究现状．现代壳模型理论计算表明。He的基态自旋宇称为1／2^+，而不是1／2^-，即存在自旋宇称翻转现象．到目前为止，实验上虽然观测到了^9He的几个共振态，但还不能确认其基态的能量和自旋宇称值．利用新的实验技术——逆运动学弹性共振散射，对^9He核进行研究，给出了共振态的自旋宇称可能的取值范围．在ISOL型次级束装置上的实验有望能给出^9He核能级的精确测量．The status of theoretical and experimental investigations on unbound nucleus()~(9)He is briefly introduced. The results of modern shell model suggest that the ground state of~(9)He should be 1/2~(+) instead of 1/2~(- )as expected by the normal shell ordering. Therefore, it means that the parity inversion which was well known in~(11)Be occurs also in~(9)He ground state. Recently, some resonance states were observed in transfer reactions and final-state reaction, but their spin-parities cannot be exact...