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。     

Reaction rate of 24Mg(p,γ)25Al

The proton-capture reaction on ²⁴Mg has been investigated in the bombarding energy range of E_p=0.2–1.7 MeV. Resonance properties (strengths, branching ratios and lifetimes) of low-energy resonances have been measured. From the experimental results, accurate proton partial widths, γ-ray partial widths and total widths (Γ_p, Γ_γ, and Γ) have been deduced. The present experimental information establishes the ²⁴Mg+p reaction rates over the temperature range T=0.02–2.0 GK with statistical uncertainties of 5% to 21%. Our recommended reaction rates deviate from previous estimates by 18% to 45%. Based on our results, we can rule out the recent suggestion that the total width of the E_R=223 keV resonance has a significant influence on the reaction rates. We also discuss several effects that might give rise to systematic uncertainties in the reaction rates. The astrophysical implications for hydrogen burning of ²⁴Mg at low stellar temperatures are presented.     

22Na(p,γ)23Mg反应的实验研究

讨论了目前有关22Na(p,γ)23Mg反应的实验研究工作,结合兰州放射性束流线上的放射性束流23Al的β+延发质子衰变实验的测量结果,给出了23Al延发衰变的质子能谱,并比较了近期实验给出的相关能级的自旋、宇称值,正是由于这种自旋、宇称和能级部分宽度的不确定性,导致了反应率计算的不确定性. 计算了同位旋相似态的共振强度. 对于测量到的新的延发衰变能级Ed=8.916MeV,由于没有相应的能级宽度值,实验仅给出其相对共振强度值.     

Search for low-energy resonances in 27Al(p, α)24Mg

The known low-energy resonances in ²⁷Al(p, γ)²⁸Si at e_R = 203, 223, 293 and 327 keV have been searched for in the ²⁷Al(p, α)²⁴Mg reaction. The observed upper limits for the resonance strength together with the results from previous work show that the MgAl cycle is not closed at all stellar temperatures of interest and that in the important temperature range near T₉ = 0.1 the (p, γ) reaction proceeds at least 100 times faster than the (p, α) reaction. The results might be of importance for the explanation of extinct ²⁶Al in meteoritic samples as well as of the 4 solar masses of ²⁶Al found in the interstellar medium via γ-astronomy.     

Polarization Features of the 24Mg(2+) Nucleus Produced in the Reaction 27Al(p, α)24Mg(2+)

At the proton energy of E_p = 7.4 MeV, the double-differential cross sections for the reaction ²⁷Al(p, α₁γ)²⁴Mg were measured for 11 values of the alpha-particle emission angle in the range of θ_α = 30°–160°(lab). All even components of the density-matrix spin-tensors were reconstructed for the oriented ²⁴Mg nucleus in the 2⁺ state at 1.369 MeV, and the polarization features of this nucleus, including the populations of magnetic sublevels of the nucleus for all spin projections, multipole-moment orientation tensors, and the quadrupole and hexadecapole tensor polarizations, were determined. Relevant experimental results were compared with their counterparts calculated for the triton-pickup mechanism within the coupled-channel method and in the statistical limit of the compound-nucleus model.

     

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.     

The Mg(p, γ)Al reaction at low astrophysical energies

In the present work we report on a new measurement of resonance strengths ωγ in the reaction ²⁵Mg(p, γ)²⁶Al at Ecm=92 and 189 keV. This study was performed at the LUNA facility in the Gran Sasso underground laboratory using a 4π BGO summing crystal. For the first time the 92 keV resonance was directly observed and a resonance strength ωγ=(2.9±0.6)×¹⁰−10 eV was determined. Additionally, the γ-ray branchings and strength of the 189 keV resonance were studied with a high resolution HPGe detector yielding an ωγ value in agreement with the BGO measurement, but 20% larger compared to previous works.     

Mg,O共掺杂实现p型AlN的第一性原理研究

采用密度泛函理论下的第一性原理平面波超软赝势方法研究了纤锌矿本征AlN,Mg单掺杂AlN和Mg,O共掺杂AlN体系的晶格参数、能带结构、电子态密度、差分电荷密度及电子布居数.计算结果显示:在Mg,O共掺杂AlN体系中,激活施主O原子的引入能使受主能级降低,形成浅受主掺杂.同时,体系的非局域化特征显著,受主能带变宽.因而提高了Mg原子的受主掺杂浓度和系统的稳定性.Mg,O共掺杂更有利于制备p型AlN.     

(p,n)和(p,2n)反应激发函数的系统学研究

从普朗克(Planck)黑体辐射公式和实验测量数据出发,采用唯象的方法提出了包含两个可调参量,入射质子能量从阈能到150MeV,靶核质量数在44相似文献   

p,p在北京谱仪(Ⅱ)中的行为研究

从Monte Calor模拟和北京谱仪(BESⅡ)所取的实验数据入手,分析了p和p产生次级带电径迹和中性径迹的几率以及好径迹选择条件对这些次级径迹的去除情况、p在探测器中的能量损失和p的湮没、p和p在桶部簇射计数器中沉积能量的分布以及3种不同的粒子鉴别方法的优劣.给出了BES目前可以正确重建出的p和p的动量的最小值和利用TOF和dE?dx的联合信息鉴别p和p的优越性.     

Resonant nuclear reaction ~(23)Mg(p,γ) ~(24)Al in strongly screening magnetized neutron star crust

Based on the relativistic theory of superstrong magnetic fields(SMF), by using three models those of Lai(LD), Fushiki(FGP), and our own(LJ), we investigate the influence of SMFs due to strong electron screening(SES) on the nuclear reaction ~(23)Mg(p,γ) ~(24)Al in magnetars. In a relatively low density environment(e.g., ρ_7 0.01)and 1 B_(12) 10~2, our screening rates are in good agreement with those of LD and FGP. However, in relatively high magnetic fields(e.g., B_(12) 10~2), our reaction rates can be 1.58 times and about three orders of magnitude larger than those of FGP and LD, respectively(B_(12), ρ~7 are in units of 10~(12)G, 10~7 g cm~(-3)). The significant increase of strong screening rate can imply that more ~(23)Mg will escape from the Ne-Na cycle due to SES in a SMF. As a consequence,the next reaction, ~(24)Al(+β, ν) ~(24)Mg, will produce more ~(24)Mg to participate in the Mg-Al cycle. Thus, it may lead to synthesis of a large amount of A20 nuclides in magnetars.     

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.     

The first excited state in 23Al and its influence on 22Mg(p,γ)23Al

The excitation energy of the first excited state in ²³Al was determined by the ²⁴Mg(⁷Li, ⁸He) reaction. The state is observed to be at 460 ± 60 keV and belongs to the first excited A = 23 isospin quartet. The results are used to compute the coefficients of the isobaric multiplet mass equation. The influence of this state, a resonance in the ²²Mg(p,γ) channel, on the reaction flow in rp-process nucleosynthesis is discussed in detail.     

关于介分子离子(αp,μ~-)和(αp,2μ~-)

应用ACQM理论和方法研究介分子离子(αp,μ~-)和(αp,2μ~-).发现(αp,μ~-)的基态(X~2Σ~+)为排斥态;(αp,2μ~-)为束缚态,平衡核间距R_e=0.0078bohr,能量极小值E=-551.78a.u.     

Direct measurements of ²²Na(p,γ)²³Mg resonances and consequences for ²²Na production in classical novae

The radionuclide 22Na is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the 22Na(p,γ)23Mg reaction. We have measured the strengths of low-energy 22Na(p,γ)23Mg resonances directly and absolutely using a radioactive 22Na target. We find the strengths of resonances at Ep=213, 288, 454, and 610 keV to be higher than previous measurements by factors of 2.4-3.2, and we exclude important contributions to the rate from proposed resonances at Ep=198, 209, and 232 keV. The 22Na abundances expected in the ejecta of classical novae are reduced by a factor of ≈2.     

Excitation functions of 40Ar(p,p′γ)40Ar and 40Ar(p,γ)41K reactions

The excitation functions of ⁴⁰Ar(p,p′γ)⁴⁰Ar and ⁴⁰Ar(p,γ)⁴¹K reactions are measured in the E _p = 1.0–3.0 eV range of accelerated protons. The excitation function in the E _p > 2.6 MeV range of accelerated protons is measured for the first time. The strengths of all (more than 200) measured resonance states are calculated.     

~(58)Ni(n,p),~(60)Ni(n,p),~(62)Ni(n,α)和~(54)Fe(n,p)反应截面的测量与评价

本实验用活化法测量了中子能量在13.60 MeV—17.77 MeV的~(58)Ni(n,p)~(58m+g)Co,~(60)Ni(n,p)~(60)Co和~(62)Ni(n,α)~(59)Fe三个反应道的反应截面值,并计算了反应截面测量误差的协方差矩阵。实验的测量误差在3％—7％范围内。本文还对上述三个反应截面及~(54)Fe(n,p)~(54)Mn反应截面进行了编译,推荐了从阈能到20MeV能区的激发曲线。