利用磁谱仪研究原子核的β衰变

在原子核β衰变费米理论的基础上,利用近代物理实验中的磁谱仪测量了90Sr-90Y β放射源的动量分布,进而研究它的库里厄(Kurie)图.结合β衰变容许跃迁和禁戒跃迁的库里厄图特征,对实验数据进行了形状因子S1的改正,得到的数据能和90Sr-90Yβ放射源的跃迁性质、原子核能级自旋和宇称相吻合,有助于学生对原子核β衰变更深入的认识和进一步扩展近物实验的研究内容.     

等待点N=82附近核素β~-衰变寿命的研究

利用提出的远离稳定线附近的原子核β-衰变寿命的指数规律理论计算公式,对N=82附近快中子过程中等待点核素的β-衰变寿命进行了理论计算,比较了所获得的计算结果与最新的理论结果和实验结果并加以讨论.研究表明,相对于理论复杂和计算时间长的微观理论计算而言,利用考虑壳效应的远离稳定线的原子核β-衰变寿命指数规律理论计算公式能较快且准确地得出快中子俘获过程(R过程)等待点核素的β-衰变寿命.这能为R过程核素合成网络计算研究提供有效可靠的重要物理输入,并对今后天体中核素的合成研究具有重要意义.     

原子核双β衰变和轻子数不守恒

 原子核双β衰变实质上是二个单β衰变同时发生的过程,是一个二级弱相互作用过程.原子核单β衰变的一个典型过程是中子衰变为质子,并放出电子和反中微子,即n→p+e^-+（?）_e。自从1914年查德威克测量β衰变的连续谱以来,β衰变的研究一直是原子核物理和粒子物理的重要研究课题之一.我们知道,李政道和杨振宁提出的宇称不守恒定律,就是吴健雄通过原子核的β衰变研究而得到实验证实的.无独有偶的是原子核双β衰变的研究和自然界的另一重要守恒定律--轻子数守恒律是否破坏密切相关.     

丰中子氮同位素β-衰变的理论研究

使用壳模型系统地研究了丰中子氮同位素的β^-衰变,并对其衰变子核^18,19,20,21O的能级结构性质给出理论计算,所得结果与实验符合较好.研究了^18,19,20N核的Gamow-Teller允许型β^-衰变的特性,对与近期实验观测不一致之处进行了讨论和分析.预言了²¹N的β^-衰变及其子核高激发态的能级结构性质.这些计算将对氮同位素的实验研究很有帮助. 关键词： 中子滴线 -衰变')" href="#">β^-衰变 氮同位素 壳模型     

原子核Gamow-Teller共振和β衰变寿命的超越平均场描述

原子核的β衰变是决定宇宙中从铁到铀重元素合成的关键核过程之一。原子核β衰变的主导核跃迁是Gamow-Teller(GT)跃迁,因此,研究原子核β衰变寿命的关键是准确描述原子核的GT跃迁。描述原子核GT跃迁和β衰变寿命最常用的理论模型之一为无规相位近似(RPA)模型。然而,由于该模型仅考虑了一粒子一空穴激发组态,因此无法给出GT共振宽度,并容易高估β衰变寿命。为了克服上述困难,基于Skyrme密度泛函,发展了包含粒子振动耦合效应的无规相位近似(RPA+PVC)模型。相比于RPA模型,该模型在组态空间进一步考虑了一粒子一空穴和声子的耦合组态,从而包含了超越平均场的多体关联效应。为了推广至开壳原子核的研究,进一步考虑了对关联效应,发展了包含准粒子振动耦合效应的准粒子无规相位近似(QRPA+QPVC)模型。基于上述模型,研究了幻数原子核和超流原子核的GT跃迁、β衰变和β+/电子俘获。研究发现,采用同一组Skyrme相互作用参数SkM*,上述模型能够重现实验测量的GT共振宽度和跃迁强度分布,部分解释实验观测的GT跃迁强度压低问题,并同时改进对β衰变寿命的描述。该文针对上述最新研究进展进行了综述,并对将来的发展方向给出展望。     

利用多普勒移动衰减法研究46Ti核的激发态能级寿命

原子核的能级寿命直接反映了其内部的结构信息,是核性质研究中一个十分重要的物理参量。本工作报道了依托兰州重离子加速器装置,首次采取多普勒移动衰减法(DSAM)开展的原子核能级寿命测量。采取核反应¹²C(³⁶Ar,2p)来布居⁴⁶Ti的高激发态,利用新组建的大型高纯锗(HPGe)探测器阵列进行符合测量。根据γ能谱分别提取了4⁺、5^-、6^-态的能级寿命,并得到了这些态的跃迁概率。理论上采取大规模组态混合壳模型进行计算,并得出了能级的组态信息。     

sd壳层极丰质子核的β延迟衰变谱学

远离β稳定线原子核的结构是当前核物理领域的一个前沿热点。β衰变谱学是研究核结构的重要方法,尤其适用于低产额的滴线核。本文回顾了近年来在RIBLL1装置上开展的sd壳区极丰质子核β延迟衰变谱学的实验研究。该工作获得了15个原子核精确的半衰期、衰变子核的质量、β延迟的质子和双质子发射以及$\gamma $跃迁的能谱、分支比和比较半衰期等数据,并重建了衰变纲图,大大丰富了此区域内质子滴线附近原子核的衰变谱学信息。还介绍了探测器阵列和实验方法,概括了所研究核的衰变性质和半衰期等。特别地,对几个典型核,20Mg和22Si以及26P和27S的衰变性质进行了阐述。此外,对相关话题,如三体力、镜像核衰变不对称性、与银河系中26Al超丰问题相关的热核反应率等问题进行了探讨。     

质子放射性和质子衰变

“质子衰变”一词,可以有两个意思:其一,如同α衰变、β衰变,指原子核在衰变过程中释放出α粒子、β粒子,质子衰变,即指放射出质子;其二,指质子本身可能不稳定,要衰变为其它的粒子.为了区分两者,现巳把前一种现象称之为质子放射性,后一种称为质子衰变.无论对那一种现象的研究,在近年来都取得了很大的进展.1.质子放射性 在稳定的原子核中,中子数和质子数有一定比例。当原子核内的中子数少到一定程度时(缺中子核素),从原子核的结合能的变化规律可以知道,原子核能够以释放质子来达到稳定[1].但是,在1982年之前,在实验中只找到一个从原子核同质…     

理论研究OH+离子电子态光谱及跃迁性质

采用高精度的内收缩多参考组态相互作用方法（icMRCI）计算OH⁺离子基态和低激发态的势能曲线和A³П-X³Σ^-跃迁体系的跃迁偶极矩。计算过程中考虑了能量的Davidson修正（+Q）效应和标量相对论修正。根据势能曲线,通过求解核的一维Schrödinger方程得到OH⁺的光谱参数。通过计算A³П-X³Σ^-体系的跃迁偶极矩研究这一跃迁体系的Einstein系数、F-C因子。研究了A³П（ν'=0~6）态的跃迁辐射寿命,结果显示其数量级为10^-6 s。     

β衰变对物理学基本规律的两次冲击

 β衰变是一种放射性衰变过程,在此过程中原子核放出一个正（或负）电子,或者吸收一个在轨道上的电子而衰变成另一种原子核。β衰变的研究对原子核物理和粒子物理的发展作出了巨大的贡献。特别应该指出的是,它曾经两次冲击物理学的基本规律:一次是在查德威克发现β射线能量的连续分布以后,尼尔斯·玻尔怀疑在β衰变中能量是否仍然守恒,后来泡利提出中微子假说成功地解释了β连续谱,“挽救”了能量守恒定律;另一次是在1956年,为了解释“θ-t”之谜,李政道和杨振宁提出了在弱作用中宇称不守恒的假说,后来吴健雄等人通过极化⁶⁰Coβ衰变实验证实了李、杨的预言。     

β~--Decay Half-Lives for Waiting Point Nuclei Around N=126

We have systematically analyzed the experimental β--decay half-lives of waiting point heavy nuclei around neutron number N = 126. A new set of parameters for the exponential formula of β~--decay half-lives is proposed. The forbidden transition effects are included in the new set of parameters self-consistently. Theoretical β~--decay half-lives of nuclei around N = 126 are compared with recent theoretical results and experimental data. It is found that the new theoretical results are in better agreement with experimental data. The unknown β~--decay half-lives of some nuclei in this region are predicted for studies on nuclear structure far from stability and the nucleosynthesis in stars.     

r-过程路径核β——衰变半衰期的估算

分析了20 < A < 190范围内丰中子核β衰变的实验数据,根据半衰期随质子数、中子数以及衰变能变化所呈现的壳效应和对效应等特点,提出了一种有效估算丰中子核β衰变寿命的公式。新的计算公式形式简单包含了较少的参数、计算量小。用该公式能较为准确地再现丰中子核的β衰变半衰期。用RIKEN最新测量丰中子核半衰期检验了该公式的外推能力,本工作可以为r-过程研究提供可靠的输入数据。Experimental data of the β--decay half-lives for the nuclei with atomic number between 20 and 190 are investigated. We have systematically studied the shell effects and pairing effects on β--decay half-lives versus the decay energy Q and nucleon numbers (Z, N). An empirical formula has been proposed to calculate the β--decay half-lives of neutron-rich nuclei. The empirical formula is simple and has relatively few parameters. Experimental β--decay half-lives of the neutron-rich nuclei are well reproduced by the new formula. In addition, the extrapolating capacity of this formula has been checked with the very recent experimental data from RIKEN. The predicted half-lives for r-process relevant nuclei with the current formula can be served as the reliable input of r-process model calculations.     

Simple Formula of β+-Decay Half-Lives of Nuclei Far From β-Stable Line

We generalize the formula of β⁺-decay half-lives [Phys. Rev. C 73 (2006) 014305] to include all available data of nuclei far from the β-stable line. Good agreement with experimental data is obtained by taking into account the even-odd (e-o) effect. It is shown that the e-o effect on β⁺-decay half-life is apparent for the allowed β⁺-transition, whereas it is not apparent for the first and second forbidden transitions. This demonstrates that the allowed β⁺-transition is more sensitive to the nuclear even-odd effect than the forbidden β⁺-transition. The underlying physics is discussed. This formula can be used to predict the β⁺-decay half-lives of the nuclei far from β-stability. It is useful to experimental physicists for analyzing the data of β⁺-decay.     

Calculations of the β-decay half-lives of neutron-deficient nuclei

In this work,β~+/EC decays of some medium-mass nuclei are investigated within the extended quasiparticle random-phase approximation(QRPA),where neutron-neutron,proton-proton and neutron-proton(np) pairing correlations are taken into consideration in the specialized Hartree-Fock-Bogoliubov(HFB) transformation.In addition to the pairing interaction,the Br¨uckner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions.Calculations are performed for even-even proton-rich isotopes ranging from Z =24 to Z =34.It is found that the np pairing interaction plays a significant role inβ-decay for some nuclei far from stability.Compared with other theoretical calculations,our calculations show good agreement with the available experimental data.Predictions of β-decay half-lives for some very neutron-deficient nuclei are made for reference.     

Skyrme张量相互作用对可能的等待点原子核β衰变半衰期的影响(英文)

使用基于Skyrme相互作用的HFB+QRPA模型研究N~82和126的同中子异位素链的β-衰变的半衰期。在计算中所使用的张量相互作用和同位旋标量（IS）对相互作用都是很好地被约束了的。比较了张量相互作用和IS对相互作用对半衰期的影响。IS对相互作用的强度与相应的同位旋矢量（IV）对相互作用的强度相当时,对N~82和126的同中子异位素链中有大的中子过剩的原子核的半衰期影响很微弱。而张量相互作用采用最近约束的强度时对半衰期的影响非常显著。The β-decay half-lives of N ~ 80 and 126 isotonic chains are calculated with HFB+QRPA models based on Skyrme force. In the calculations, the well constrained Skyrme tensor interaction and isoscalar spin-triplet (IS) pairing interaction are included so that to study their effects on the half-lives. The effects of tensor interaction and IS pairing interaction on the half-lives are compared. The IS pairing interaction with strength similar to that of isovector (IV) one produces only a trivial effect in N ~82 nuclei, and N ~126 nuclei with big neutron excess. While the tensor interaction with presently constrained strengths produces an obvious effect.     

Systematic study of decay properties of heaviest elements

Decay properties and stability of heaviest nuclei with Z ?? 132 are studied within the macro-microscopical approach for nuclear ground-state masses. We use phenomenological relations for the half-lives with respect to ??-decay, ??-decay and spontaneous fission. Our calculations demonstrate that the ??-stable isotopes ²⁹¹Cn and ²⁹³Cn with a half-life of about 100 years are the longest-living superheavy nuclei located on the first island of stability. We found the second island of stability of superheavy nuclei in the region of Z ?? 124 and N ?? 198. It is separated from the ??continent?? by the ??gulf?? of short-living nuclei with half-lives shorted than 1 ??s.     

Empirical formula for <Emphasis Type="Italic">β</Emphasis><Superscript>−</Superscript>-decay half-lives of r-process nuclei

Experimental data of β ^?-decay half-lives of nuclei with atomic number between 20 and 190 are investigated. A systematic formula has been proposed to calculate β ^?-decay half-lives of neutron-rich nuclei, with a particular consideration on shell and pair effects, the decay energy Q as well as the nucleon numbers (Z, N). Although the formula has relatively few parameters, it reproduces the experimental —decay half-lives of neutron-rich nuclei very well. The predicted half-lives for the r-process relevant nuclei obtained with the current formula serve as reliable input in the r-process model calculations.     

A self-consistent mean-field study of Z = 120 nuclei and α-decay chains of 292,298,299,300,304120 isotopes

A self-consistent mean-field investigation is done to test the model accuracy, model dependence, and the dependence on different model parameters in the study of superheavy nuclei. This is done within the self-consistent mean-field models-the Skyrme-Hartree-Fock-Bogoliubov (HFB), and the Relativistic-Hartree-Bogoliubov (RHB) with density-dependent couplings. A systematic comparison is made with experimental data, as well as with the macro-microscopic Finite Range Droplet Model(FRDM). The bulk ground state properties and the microscopic structure of Z=120 superheavy nuclei are investigated. Further investigation is made of α-decay series for the five isotopes ^{292,298,299,300,304}120 of Z=120 nuclei. A spontaneous fission investigation is done to account the number of α-decay before spontaneous fission starts. The experimental data available for α-decay energies and half-lives are produced reasonably. The RHB model with NL3* parameter set, and with ImSahu and UNIV2 formula to calculate the α-decay half-lives is found to be the best suited for accurately predicting the ground state properties and the α-decay half-lives of the superheavy nuclei.