Influence of breakup on elastic and α-production channels in the ~6Li+~(116)Sn reaction

The effects of breakup reactions on elastic and α-production channels for the ~6Li+~(116)Sn system have been investigated at energies below and near the Coulomb barrier. The angular distributions of α-particle production differential cross sections have been obtained at several projectile energies between 22 and 40 MeV. The measured breakup α-particle differential cross sections and elastic scattering angular distributions have been compared with the predictions of continuum-discretized coupled channels(CDCC) calculations. The influence of breakup coupling has also been investigated by extracting dynamic polarization potentials(DPP) from the CDCC calculations. From the predictions of CDCC calculations the relative importance of the nuclear, Coulomb, and total breakup contributions have also been investigated. The nuclear breakup couplings are observed to play an important role in comparison to the Coulomb breakup for the direct breakup mechanisms associated in the reaction of ~6Li projectile with ~(116)Sn target nuclei. The influence of strong nuclear breakup coupling exhibits suppression in the Coulomb-nuclear interference peak. The direct breakup cross sections from the CDCC calculations under-predict the measured α-particle differential cross sections at all energies. This suggests that the measured α particles may also have contributions from other possible breakup reaction channels.     

Coulomb and nuclear interactions in the dynamics of weakly-bound neutron-halo breakup on heavy target

Within our aim to clarify some aspects of the breakup dynamics of loosely-bound neutron-halo projectiles on a heavy target,we apply the continuum discretized coupled-channel formalism to investigate the beryllium¹¹Be breakup on a lead²⁰⁸Pb target atE_lab=140 MeV incident energy.By evidencing that the continuum–continuum couplings are much stronger in the nuclear breakup than in the Coulomb breakup,we conclude that the strength of these couplings in the total breakup is dominated by the nuclear contribution,with the diagonal monopole nuclear potential in the projectile–target center-of-mass having negligible effect on the total and nuclear breakup cross-sections.For this kind of reaction,we show that the condition for the total breakup to approach its dominant component in the absorption region is strongly dependent on the continuum–continuum couplings and the diagonal monopole nuclear potential.     

Deuteron inelastic scattering on 6Li and 7Li nuclei within the three-body cluster model

The problem of the deuteron interaction with lithium nuclei,treated as a system of two coupled pointlike clusters,is formulated to calculate the cross sections of the d+Li reaction.The d+Li reaction mechanism is described using the Faddeev theory for the three-body problem of deuteron-nucleus interaction.This theory is slightly extended for calculation of the stripping processes ^6Li(d,p)^7Li,^7Li(d,p)^8 ,^6Li(d,n)^7 Be,and ^7Li(d,n)^8 Be,as well as fragmentation reactions yielding tritium,a-particles,and continuous neutrons and protons in the initial deuteron kineticenergy region Ed=0.5-20 MeV.The phase shifts found for d+^6Li and d+^7Li elastic scattering,as part of the simple optic model with a complex central potential,were used to find the cross sections for the 6^Li(d,yM)^8 and ^7Li(d,yE1)^9 Be radiation captures.The three-body dynamics role is also summarized to demonstrate its significant influence within the d+^7Li system.     

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上的破裂反应

25 MeV/u 6He+9Be反应的实验中利用多个探测器望远镜对反应产物进行了测量, 对实验中各个角度测量到的4He进行观察, 将其中两个有高能峰成分的探测器划分成三部分, 得到不同角度4He的单举能谱和破裂产生4He的微分截面. Different products of 6He nuclei from 9Be target has been measured with a 6He beam at energy of 25 MeV/u. The energy spectra at different angles for 4He isotope were analyzed and the experiment differential cross sections for the direct breakup reaction were obtained.     

活性靶技术熔合截面测量极限研究

天体环境中丰中子核素熔合反应率对研究中子星表面超级暴现象的点火机制有重要意义。由于次级束流强过低,无法使用传统固体靶实验技术测量垒下熔合反应截面。活性靶技术的发展为垒下丰中子核素熔合反应截面的测量提供了可行的途径。基于Geant4模拟详细地分析了多重采样电离室（MUSIC）与时间投影室（TPC）两种活性靶探测器中熔合反应与弹性散射的运动学性质,给出了4种熔合反应鉴别判据,并且计算了由这些判据误判引起的熔合截面系统误差。在E_cm=13.6 MeV时,MUSIC与TPC的弹性散射误判截面分别为0.5 mb和2.9×10-3 mb,都远小于此时熔合截面（877 mb）。在垒下,MSUIC的熔合截面系统误差已经超出实验测量要求,而TPC能够进行实验测量的能量可以降低至E_cm=4.7 MeV。Reaction rates of fusion reactions among neutron-rich nuclei in the astrophysical environment are of great significance to understand the ignition of superbursts on neutron stars. Since beam intensity is rather low for radioactive ion beams, it is extremely difficult to operate a direct measurement for cross sections of such fusion reactions below the Coulomb barrier using thick target technique. In this case, a novel technique, active target technique, has been developed recently. To study the energy limit for measurement below Coulomb barrier, the kinematics of elastic scattering and fusion reaction in MUSIC and TPC are discussed with Geant4 simulation. Four identification methods are used and uncertainties of cross sections resulted from misjudgments are calculated. With E_cm=13.6 MeV, the uncertainties of cross sections for MUSIC and TPC are 0.5 mb and 2.9×10-3 mb, respectively. The uncertainties for MUSIC become far beyond measurement when below coulomb barrier, while TPC remains to be a suitable detector for measuring fusion cross sections until E_cm=4.7 MeV.     

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.     

MEND——-—个计算250 MeV以下中重核数据的程序(英文)

基于球型光学模型、 预平衡发射和Hauser Feshbach统计等理论, 编制了MEND程序（Medium Energy Nuclear Data）, 该程序适用于中重原子核在入射粒子能量低于250 MeV的中低能区的全套核数据计算。对于中子和质子在250 MeV以下诱发的核反应, 其全截面、 反应截面、 弹性散射微分截面、 双微分截面和能谱等理论计算值与相应的实验值基本一致。MEND是计算中低能核反应的基础程序, 在我国已被广泛用于核数据计算及建立中能核数据库Based on the spherical optical model, pre equilibrium statistical theory, and Hauser Feshbach theory, etc., the code MEND (Medium Energy Nuclear Data) is written for calculating the complete set of nuclear data of medium heavy nuclei in medium low energy region (≤250 MeV). For the reactions induced by neutron and proton below 250 MeV, the total cross sections, reaction cross sections, elastic scattering differential cross sections, double differential cross sections and energy spectra, etc. calculated by the code MEND, generally agree with those corresponding experimental data. MEND is a foundational program for nuclear reaction in medium low energy region and is wildely used for nuclear data calculation and establishing ENDF/B6 format files of medium low energy region in China.     

Theoretical Analysis of Neutron Double-Differential Cross Sections of n ＋^9Be Reactions

By using the nuclear reaction model for light nuclei, the calculations of the double-differential cross sections of outgoing neutrons from n ＋^9Be reactions are performed. The total outgoing neutrons are only come from the （n, 2n）2a reaction channel. The （n, 2n）2a reaction channel is achieved through six different reaction approach, which are illustrated in this paper. The calculated results agree very well with the measured data at En = 7.1, 8.09, 8.17, 9.09, 9.97 and 10.26 MeV, because the updated level schemes related to the n ＋ ^9Be reactions have been employed in this calculations.     

Measurement of(n,α)and(n,2n)reaction cross sections at a neutron energy of 14.92±0.02 MeV for potassium and copper with uncertainty propagation

Experimentally measured neutron activation cross sections are presented for the ⁶⁵Cu(n,0)^62mCu,⁴¹ K(n,a)^38Cl,and ⁶⁵Cu(n.2n)⁶⁴Cu reactions with detailed uncertainty propagation.The neutron cross secions were measured at an incident energy of 14.92±0.02 MeV,and the neutrons were based on the(d,n)a fusion reaction.The ²⁷ Al(n,a)²⁴Na reaction was used as a reference reaction for the normalization of the neutron flux.The pre-calib-rated lead-shielded HPGe detector was used to detect the residues'γ-ray spetra.The data from the measured cross sections are compared to the previously measured cross sections from the EXFOR database,theoretically calculated cross sections using the TALYS and EMPIRE codes,and evaluated nuclear data.     

Proton Elastic Scattering from ^14Be and Halo Effects

The elastic scattering of p-^14Be system at Elab = 200 MeV is evaluated within the relativistic impulse approximation. We discuss the effects of the halo neutrons on the three observables of the elastic scattering system, such as differential cross section dσ/ dΩ, analyzing power Ay and spin rotation Q. The results of the three observables of the elastic scattering of p-^14Be system are compared with those of p-^12C and p-^16O systems at the same energy as E1ab = 200 MeV. We have found that in the small angular region the Ay and Q, as well as dσ/dΩ, are quite sensitive to the nucleon density distributions on the surface of the target nucleus and offer some unique behaviors of halo nuclei.     

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.     

THE STUDIES OF NON-RUTHERFORD BACKSCATTERING CROSS SECTIONS OF 4He FROM 16O

In this article, we report the 170° backscattering cross sections of ⁴He from ¹⁶O in the energy range of 2.0-9.0 MeV. Our measurements show that the alpha-oxygen scattering remains Rutherford scattering up to E_α=2.35 MeV, and there exist two energy regions, namely 5.55-5.85MeV and 8.50-8.80MeV, where the cross sections are enhanced and show a smooth variation. The measured laboratory cross sections are 9.50-9.97 and 35.0-33.0 times greater than the Rutherford values, respectively. In the 8.50-8.80MeV region, the cross sections at scattering angles of 160°, 165°, 170° and 175° were measured and found to be strongly angle-dependent. A most strong resonance occurred at 7.60 MeV, where the cross section is 200 times of its Rutherford value. This resonance has been used to measure the ¹⁶O concentration on a Cu surface, with a sensitivity of 1×10¹⁵ oxygen atoms/cm², Besides, we have studied the backscattering angle dependence of the threshold energy, i.e., the energy at which the elastic cross section begins to deviate from its Rutherford value. The experimental result seems not in agreement with the prediction made from the analytical formula developed by Bozoian et al.     

Theoretical Prediction of Differential Cross Sections for Reaction pp → pK^＋A in a Resonance Model

The reaction of pp → pK^＋A is a very good channel to study N^＊ resonances through their KA decay mode, because there is no mixing of isospin I = 1/2 and I = 3/2 due to isospin conservation. In this work, we extend a resonance model, which can reproduce the total cross section very well, to offer differential cross section information about this reaction. It can serve as a reference to build the scheduled hadron detector at Lanzhou Cooler Storage Ring （CSR）. Experiment measurement of these differential cross sections in the future will supply us more constraints on the model and help us understanding the strangeness production dynamics better.     

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.     

Theoretical Study of Isotopic Effect of Oxygen Atom on the Stereodynamics for the O（^3P） ＋ D2 → OD ＋ D Reaction

Quasi-classical trajectory theory is used to study the isotope effect of oxygen atoms on the vector correlations in the O（^3P） ＋ D reaction at a collision energy of 25kcal/mol using accurate potential energy surface of the 3A＇ triplet state. The distributions of p（θr） and the distribution of dihedral angel p（φr） as well as p（θr,φr） are calculated. Moreover, four polarization-dependent generalized differential cross sections （PDDCSs） of product are presented in the center-of-mass frame. The results indicate that the polarization of the product presents different characters for the isotope effect of oxygen atoms. Isotopic substitute can cause obviously different effects on the four PDDCSs.     

1H(17F,α)14O反应截面测量

14O （α,p）17F是天体X射线暴中重要的突破反应。本工作通过厚靶方法测量其逆反应1H （17F,α）14O的反应截面来研究这一关键反应。本实验工作是在日本东京大学原子核科学研究中心（CNS）的低能次级束流线（CRIB）上完成的,后续的扣除本底实验是在兰州放射性束流线（RIBLL1）上完成的。CRIB实验是通过2H （16O,n）17F转移反应产生17F次级束,经过CRIB分离提纯之后,利用该次级束轰击氢气靶。在氢气靶后布置了三套望远镜探测器系统,用以探测不同实验角度的反冲α粒子,在数据处理的过程中经过动力学重构后得到了1H （17F,α）14O反应在质心系能区E_c.m.=2.7~3.4 MeV的反应截面。实验结果在3 MeV以上的高能区与前人的薄靶实验数据是一致的,在低能区本工作获得了新的实验数据,倾向于支持干涉相消的理论预言结果。The 14O(α, p)17F reaction is one of the important breakout reactions in type I X-ray burst. This work reported a new cross section measurement of its reverse reaction of 1H(17F,α)14O. The experiment was performed using the CNS radioactive ion beam separator (CRIB), located at the Center for Nuclear Study (CNS), the University of Tokyo. The sequent background measurement was carried out at Radioactive Beam Line in Lanzhou (RIBLL1). 17F beam was produced via the transfer reaction of 2H(16O, n)17F, subsequently separated and purified by CRIB and bombarded a thick hydrogen H₂ gas target. The recoiling α particles were measured by three △E-E silicon telescopes at three different angles. The total cross sections of 1H(17F,α)14O have been derived at E_c.m.=2.7~3.4 MeV based on an isotropic angular distribution assumption. Our results are consistent with the previous ones in the energy region of E_c.m.>3 MeV, and we also obtained some new data in the low energy region, which partly support the destructive interference between the direct and resonant reaction mechanism predicted by the theory.     

Differential and Integral Cross Sections for Electron Impact Excitation of Lithium

The differential and integral cross sections for electron impact excitation of lithium from the ground state 1s22s to excited states 1s22p, 1s23l （l=s, p, d） and 1s24l （l=s, p, d, f）at incident energies ranging from 5 eV to 25 eV are calculated by using a full relativistic distorted wave method. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbitals are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. A part of the cross sections are compared with the available experimental data and with the previous theoretical values. It is found that, for the integral cross sections, the present calculations are in good agreement with the time-independent distorted wave method calculation, for differential cross sections, our results agree with the experimental data very well.     

MENDF—一个计算200 MeV以下裂变核数据的程序(英文)

基于球型光学模型、 预平衡发射和Hauser-Feshbach统计等理论, 编制了MENDF（Medium Energy Nuclear Data for Fission）程序, 该程序适用于裂变核在入射粒子能量低于200 MeV的中低能区的全套核数据计算。 对于中子和质子在200 MeV以下诱发的核反应, 其全截面、 反应截面、 弹性散射微分截面、 裂变截面和裂变中子谱、 5种发射粒子的单举截面和相应的能谱等理论计算值与相应的实验值基本符合。 MENDF在我国已被广泛用于核数据计算及建立中能核数据库。Based on the spherical optical model, pre equilibrium and Hauser Feshbach statistical theory, the code MENDF (Medium Energy Nuclear Data for Fission) is written to calculate a complete set of nuclear data for fission nuclei in the medium low energy region (≤200 MeV). For neutron and proton induced reactions below 200 MeV, the total cross sections, reaction cross sections, elastic scattering differential cross sections, fission cross section, energy spectra of fission neutron and five kinds of emitting particles, etc. are calculated by MENDF. The calculated data generally agree with their corresponding experimental data. MENDF is widely used for nuclear data calculation and to establish ENDF 6 formatted files for the medium low energy region in China.