3M⊙ AGB星中26Al核合成的网络计算和反应率灵敏度分析

研究了3$M_{\odot}$AGB星中26Al核合成的网络计算和核反应率的灵敏度分析。结合最新的核反应率数据,建立了一个从碳到硅完整的核反应网络,计算了26Al的丰度。结果表明,26Al首先在AGB星中有效合成,随着核反应的进行,然后被一系列的核反应消耗。MgAl循环出现在26Al的网络中。我们将核反应网络中的主要核反应分为三类:(n, ${\rm{\gamma }}$),(p,${\rm{\gamma }}$)和($\alpha$, ${\rm{\gamma }}$),并对核反应率的灵敏度进行了详细的分析。已经确定了每一类中最有影响的核反应,它们是25Mg(n, ${\rm{\gamma }}$)26Mg,25Mg(p, ${\rm{\gamma }}$)26Al,26Mg(p, ${\rm{\gamma }}$)27Al,21Ne(p, ${\rm{\gamma }}$)22Na,18O($\alpha$, ${\rm{\gamma }}$)22Ne和22Ne($\alpha$,${\rm{\gamma }}$)26Mg。在目前网络所涉及的所有核反应中,25Mg(p, ${\rm{\gamma }}$)26Al是对26Al的产量有最大的影响,它值得核实验物理学家的关注。     

利用18O(6Li,d)22Ne反应研究22Ne Eα=470 keV共振态的性质

慢速中子俘获过程（s过程）是合成比铁重元素的重要途径之一。22Ne（α,n）25Mg反应是大质量AGB星中s过程主要的中子源,其中的22Ne主要通过14N（α,γ）18F（β+）18O（α,γ）22Ne反应链合成。该反应链中关键反应18O（α,γ）22Ne在天体物理感兴趣能区的截面非常低,其天体反应率主要来自于22Ne α分离阈附近低能共振态的贡献,但目前相关能级的共振参数严重缺失。在HI-13串列加速器的Q3D磁谱仪上,通过测量18O（6Li,d）22Ne反应的角分布,利用DWBA分析确定了22Ne分离阈附近共振能级E_α=470 keV的自旋宇称为0+,为后续计算18O（α,γ）22Ne的天体反应率打下了基础。About a half of the abundances of elements heavier than iron comes from the so-called slowneutron capture process (s-process) in Asymptotic Giant Branch (AGB) stars, with the 22Ne(α, n)25Mg reaction as one of the main neutron sources. In the beginning phase of AGB thermal pulse, 22Ne is produced by the 14N(α, γ)18F(β+)18O(α, γ)22Ne reaction sequence, in which the 18O(α, γ)22Ne reaction plays a key role. While the reaction rate of the 18O(α, γ)22Ne is mainly affected by several resonant states lying closely to the α threshold in 22Ne, up to now, the relevant 22Ne parameters are fragmentary in the energy region corresponding to the typical temperatures of s-process. The direct measurement of the 18O(α, γ)22Ne reaction rate is extremely difficult due to the very low cross section. In this work, we investigated the 22Ne resonant states via the 18O(6Li, d)22Ne reaction at the Beijing HI-13 tandem accelerator of China Institute of Atomic Energy. Based on the DWBA analysis, preliminary results showed that the spin-parity of 22Ne E_α=470 keV resonant states was assigned as 0+, which would make contributions to subsequent calculation for the reaction rate of the 18O(α, γ)22Ne.     

Astrophysical ~(22)Mg(p,γ)~(23)Al reaction rates from asymptotic normalization coefficient of ~(23)Ne→~(22)Ne+n

The radionuclide ~(22)Na generates the emission of a characteristic 1.275 MeV γ-ray. This is a potential astronomical observable, whose occurrence is suspected in classical novae. The ~(22)Mg(p, γ)~(23)Al reaction is relevant to the nucleosynthesis of ~(22)Na in Ne-rich novae. In this study, employing the adiabatic distorted wave approximation and continuum discretized coupled channel methods, the squared neutron asymptotic normalization coefficients(ANCs)231 for the virtual decay of Ne → ~(22)Ne + n were extracted, and determined as(0.483 ± 0.060) fm~(-1) and(9.7 ± 2.3) fm~(-1) for the ground state and the first excited state from the experimental angular distributions of ~(22)Ne(d, p)~(23)Ne populating the ground state and the first excited state of ~(23)Ne, respectively. Then, the squared proton ANC of ~(23)Al_(g.s.) was obtained as C_(d5/2)~(2)(~(23)Al)(2.65 ± 0.33) × 10~3 fm~(-1) according to the charge symmetry of the strong interaction. The astrophysical S-factors and reaction rates for the direct capture contribution in ~(22)Mg(p, γ)~(23)Al were also presented. Furthermore, the proton width of the first excited state of ~(23)Al was derived to be(57 ± 14) eV from the neutron ANC of its mirror state in ~(23)Ne and used to compute the contribution from the first resonance of ~(23)Al. This result demonstrates that the direct capture dominates the ~(22)Mg(p, γ)~(23)Al reaction at most temperatures of astrophysical relevance for 0.33 T_9 0.64.     

~(20)Mg β衰变谱学与~(15)O(α,γ)~(19)Ne反应（英文）

~(15)O(α,γ)~(19)Ne(p,γ)~(20)Na反应链是高温CNO循环向快速质子俘获过程突破的一条关键路径,相关的反应率输入量可通过~(20)Mg的β衰变可布居~(19)Ne共振态并测量其衰变性质来获得。通过高效率高精度地测量~(20)Mgβ衰变中产生的质子与γ射线得到了~(20)Mg衰变的详细信息,并构建了完整的衰变纲图,还进行了~(19)Ne 4 033 keV共振态衰变性质的探索,获得了该态在~(20)Mgβ衰变中被布居的分支比上限。通过比~(20)Mg和~(20)O镜像能级跃迁的结果确认了同位旋非对称性,为检验相关理论模型提供了精确的实验数据。对于突破路径中有重要影响的~(19)Ne 4 033 keV共振态的性质,有待更高统计的实验进一步研究。     

Direct measurement of the resonance strengths and branching ratios of low-energy(p, γ) reactions on Mg isotopes

Proton capture reactions on Mg isotopes are significant in the Mg-Al cycle in stellar H-burning.In particular,the resonance strengths and branching ratios of low-energy resonances in Mg(p,y)26 A1 reactions determine the production of ~(26)Al,which is one of the most important long-lived radioactive nuclei in nuclear astrophysics.In this article,we report our first experiment using the intense proton beam of approximately 2 mA provided by the JUNA accelerator ground laboratory and a new technique that can minimize the composition change of targets under intense beam irradiation.The resonance strengths and branching ratios of E=214,304,and 326 keV resonances in the reactions of ~(24)Mg(p,γ)~(26)Al,~(25)Mg(p,γ)~(26)Al,and ~(26)Mg(p,γ)~(27)Al,respectively,were measured with high accuracy.The success of this experiment provides a good calibration for the nuclear astrophysical experiment at the Jinping underground laboratory.     

Determination of the ~(25)Mg(p,γ)~(26)Al resonance strength at E_(c.m.)=58 keV via shell model calculation

The observation of 26 Al is an useful tool for γ-ray astronomy and in studies of galactic chemical evolution. The most likely mechanism for 26A1 nucleosynthesis is in the hydrogen burning Mg Al cycle, and the 26A1 production reaction 25Mg(p,γ)26Al at the important temperature range below T = 0.2 GK is still not well known. The spectroscopic factor of 58 ke V resonance level in 26A1 is determined with shell model calculation and then used to deduce the resonance strength of the 25Mg(p,γ)26Al reaction. The result provides a reference for the future 25Mg(p,γ)26Al direct measurement at Jinping underground laboratory.     

Progress of Jinping Underground laboratory for Nuclear Astrophysics (JUNA)

Jinping Underground laboratory for Nuclear Astrophysics(JUNA) will take the advantage of the ultra-low background of CJPL lab and high current accelerator based on an ECR source and a highly sensitive detector to directly study for the first time a number of crucial reactions occurring at their relevant stellar energies during the evolution of hydrostatic stars. In its first phase, JUNA aims at the direct measurements of~(25)Mg(p,γ)~(26)Al,~(19)F(p,α)~(16)O,~(13)C(α,n)~(16)O and ~(12)C(α,γ)~(16)O reactions. The experimental setup,which includes an accelerator system with high stability and high intensity, a detector system, and a shielding material with low background, will be established during the above research. The current progress of JUNA will be given.     

中国著名的物理学家——张文裕

张文裕教授是我国著名的物理学家.1910年1月9日生于福建省惠安县.1931年毕业于燕京大学物理学系.1934年考取英庚款公费赴英留学,1935年在剑桥大学卡文迪什实验室研究核物理,1938年在E.卢瑟福,C.D.艾利斯和J.D.考克饶夫指导下完成博士论文《核反应过程的共振效应与人工放射性同位素的产生》,取得博士学位.在剑桥大学期间,先后与D.W.B.路易斯,W.E.伯切姆,M.格尔德哈伯和嵯峨根等人合作,首先研究天然α射线引起~(30)P、~(28)Al和~(25)Mg的共振效应,验证了N.玻尔的液滴模型.首次研究高压倍加器产生~8Li衰变过程和激发态~8Be~*跃迁为2α,测得α连续谱线,证明~8Be~*有很宽的激发态.用倍加器产生的γ和n轰击出多种元素,形成放射性同位素.首次发现(γ,n)和(n,2n)过程并发现~(16)O(n,p)~(15)N,可预防反应堆建造和运行时冷却水的~(16)O变为~(15)N引起的辐射危害.这些成果得到物理学界好评.1943年在法国物     

25Mg(p, γ)26Al实验研究进展

长寿命放射性核素26Al是星际介质、$\gamma$射线天文学和太阳系形成研究中最重要的核素之一。最可能合成26Al的三种天体场所都与25Mg(${\rm p},\,{\rm{\gamma }}$)26Al反应相关,因此精确测量其近阈能级的共振强度和天体物理反应率对人们认识宇宙26Al的来源具有重要意义。本文回顾了25Mg(${\rm p},\,{\rm{\gamma }}$)26Al反应的实验研究方法和最新研究进展,特别是介绍了我国对该反应的间接测量实验以及直接实验测量计划。当前的间接测量结果提升了25Mg(${\rm p},\,{\rm{\gamma }}$)26Al天体物理反应率的精度,也可以帮助我们估算直接测量的产额,并优化深地直接测量的实验设计。高能点的直接测量结果与国际上其它实验结果在误差范围内符合很好,表明本项目研制的探测装置工作状态良好,能够胜任锦屏深地核天体物理实验研究。     

Measurements on diproton emission from the break-up channels of ~(23)Al and ~(22)Mg

Two-proton relative momentum distributions from the break-up channels 23Al→p+p+21Na and 22Mg→p+p+20Ne at an energy of 60-70 A MeV have been measured together with two-proton opening angles at the projectile fragment separator beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The results demonstrate the existence of diproton emission component from single-step 2He for highly excited 23Al and 22Mg.     

平面阻塞效应测量E_p=1565keV时~(27)Al(p,α)~(24)Mg共振反应寿命

采用(111)面阻塞效应测量了E_p=1565keV共振时~(27)Al(p,α)~(24)Mg核反应寿命。用解析方法分析实验数据。测到的核寿命τ=17.9_(-4.0)~(+4.4)as,与<110>轴阻塞效应测量结果和文献给出的结果在误差范围内一致。测量了E_p=1183.4keV时(111)面的α粒子的阻塞分布,并与理论计算作了比较。     

Theoretical studies of proton capture reactions in A～25 proton-rich nuclei

The direct proton capture and resonance proton capture properties of stellar reactions 22Mg(p,γ)23Al and 26Si(p,γ)27P are studied by employing a mean-field potential obtained from the Skyrme-Hartree-Fock(SHF) model.Calculations with the SHF potential reproduce well the loosely-bound structure of the ground states as well as the widths of the resonant states in these nuclei.With the obtained potential we estimate the reaction rates of direct proton capture and resonance proton capture to nuclei 23Al and 27P....     

~(50,48,46)Ti的(n,p)(n,α)和~(58)Ni的(n,2n)(n,p)反应截面的测量

本文叙述了从13.50 MeV到14.81 MeV中子能区用活化法相对~(21)Al(n,α)~(24)Na的反应截面,对~(50)Ti(n,α)~(47)Ca、~(48)Ti(n,p)~(48)Sc、~(46)Ti(n,p)~(46)Sc、~(58)Ni(n,2n)~(57)Ni、~(58)Ni(n,p)~(58m+g)Co五个反应截面的测量。并将所得的结果和其他作者的结果进行了比较。     

Proton and Two-proton Emissions from Proton-rich Nuclei with 10≦Z≦20

Proton (p) and two-proton (2p) emissions from the proton-rich nuclei with 10≦Z≦20 have been explored by the in-fight decay and implantation decay methods, respectively, in a series of experiments at the HIRFL-RIBLL facility. The in-flight 2p emissions from the excited states of 28,29S /26,27P and 17;18Ne were studied by complete-kinematics measurements. Mechanisms of 2p decay and related p-p correlations have been explored. Obvious 2p correlated emissions have been observed in the cases of 28,29S but not in 27,28P, indicating the 2p halo plays an important role in the diproton emission. In the 17;18Ne cases, a small 2p opening angles were deduced by the HBT analyses, implying the BCS-BEC crossover may occur in the dilute nuclear matter. Moreover, 27S/26P/25Si, 22Si/20Mg, 23Si/22Al/21Mg, 24Si/23Al, and 36;37Ca were implanted in a thin double-sided-silicon-strip detector and their -delayed p and 2p decays have been measured by a surrounding silicon detector array under the continuous-beam mode. Important information on the nuclear spectroscopy, such as energy, lifetime, branching-ratio, and so on, has been extracted, which helps us to understand the nuclear structures of proton-rich exotic nuclei close to the drip-line.     

利用加速器质谱方法测量14N(16O,α)26Al反应截面

Al是核天体物理非常重要的一个核素,14N(16O,α)26Al的反应截面可能是天体26Al的一个来源.介绍了利用AMS方法测量14N(16O,α)26Al反应截面的过程,包括靶的照射、化学分离、26Al原子数的AMS方法测量及最后的核反应截面值.The~(26)Al is one of the important nuclide in the astrophysics. The reaction, namely~(14)N(~(16)O, α)~(26)Al, may be one of the origin of the source of~(26)Al in the cosmic. The procedures of the cross section measurement with accelerator mass spectrometry (AMS) method are discussed, In this paper, the irradiation experiment, chemical separation and~(26)Al measurement are described. The results of cross-section (around) sub-barrier energies are also represented.     

特洛伊木马方法及其应用最新进展

特洛伊木马方法是实验核天体物理中一种重要的间接测量方法,特别适合极低能区带电粒子裸核反应截面测量。在介绍特洛伊木马方法基本原理的基础上,重点讨论该方法近期在核天体物理应用中的一些重要实验结果,以及对未来研究的展望。主要介绍:AGB星s-过程关键中子源反应$ ^{{\rm{13}}}{\rm{C(\alpha ,n}}{{\rm{)}}^{{\rm{16}}}}{\rm{O}}$的间接测量,AGB星氟丰度超常现象相关核反应间接测量,以及最近热点–中等以上质量恒星碳燃烧核反应间接测量结果及相关争议。     

星际26Al核合成的研究进展

介绍了星际 26Al衰变所发射1 809 keV γ射线的最新空间探测结果， 综述了目前关于星际 26Al起源的各种天体模型的研究进展。最后， 简要阐述了14N(p,γ)15O反应截面的最新测量结果及其对 26Al起源研究的影响， 探讨了一种星际 26Al合成的可能新途径。The recently detection outcome about interstellar 26Al is introduced, as well as the investigation progresses of interstellar 26Al nucleosynthesis in all models are reviewed. Finally, the new nuclear physics experimental results for the14N(p,γ)15O reaction effect on sources of interstellar 26Al and an alternative new way for nucleosynthesis 26Al in SNIa are discussed.     

19F+27Al深部非弹性碰撞产物的角分布

完成了19F+27Al深部非弹性碰撞产物的角分布测量.初步分析了反应产B,C,N,O,F,Ne,Na,Mg和Al的实验室系角分布,展现出深部非弹性反应机制的特点,显示了反应系统随时间的演化过程. Angular distributions of fragments produced in the deep inelastic collision of~(19)F+~(27)Al have been measured for incident energy of 114 MeV at θ_(lab)= 9~(o), 24~(o), 40~(o), 55~(o), 70~(o) and 85~(o). Angular distributions of dissipative products B, C, N, O, F, Ne, Na, Mg and Al are analyzed to provide an evolution process of the intermediate dinuclear system formed in the reaction.     

A=130区缺中子核122Cs与134Ce高自旋态研究

通过重离子核反应与在束γ谱的实验技术,对A=130缺中子核区122Cs与134Ce核的高自旋态进行了研究,所用核反应分别为107Ag(19F,1p3n)与122Sn(16O,4n).实验结果扩展了122Cs与134Ce的能级纲图.在122Cs中发现可能是属于手征二重带的结构,而在134Ce核的高自旋态结构中呈现出重要的具有不同γ形变的形状共存特性.Through heavy ion nuclear reaction and in-beam γ-ray spectroscopy technique, the high spin states of neutron-deficient~(122)Cs and~(134)Ce nuclei in A=130 region have been studied. The~(107)Ag(~(19)F, 1p3n) and~(122)Sn(~(16)O, 4n) reactions were used. The previous level schemes of~(122)Cs and~(134)Ce have been extended. Possible chiral doublet bands in~(122)Cs have been observed and a shape coexistence with different γ values in~(134)Ce are suggested.     

~(100)Mo(n,2n)~(99)Mo,~(96)Mo(n,p)~(96)Nb和~(92)Mo(n,α)~(89m+g)Zr反应截面测量

本文报告了在E_n=13.40—14.79MeV中子能区用活化法以~(27)Al(n,α)~(24)Na截面为中子注量标准测得的~(100)Mo(n,2n)~(99)Mo,~(96)Mo(n,p)~(96)Nb和~(92)Mo(n,α)~(89m+g)Zr的反应截面,中子能量是用铌锆截面比法测定的。文中将实验测量值与理论计算值进行了比较,还对上述三个反应的截面进行了编评,给出了推荐的激发曲线。