基于结团形成模型系统研究Z=82,N=126闭壳附近原子核的α衰变

基于结团形成模型（cluster-formation model,CFM）系统地研究了质子数Z=82,中子数N=126闭壳附近的α衰变母核的α衰变预形成因子P_α。计算结果表明:基于结团形成模型计算得到的P_α线性地依赖于价质子（空穴）N_p和价中子（空穴）N_n的乘积。这与前期工作[SUN X D,et al.Phys Rev C,2016, 94 （2）:024338;DENG J G,et al.Phys Rev C,2017, 96 （2）:024318]得到的结论是一致的,其中,P_α是唯象的且模型依赖的,从α衰变半衰期的理论值和实验值的比值中提取。结合前期工作可以得到这样的结论:对于Z=82,N=126闭壳附近的α衰变母核,其P_α与N_pN_n呈线性关系,且价质子-价中子相互作用在α结团预形成中起了很重要的作用。In the present work, the α decay preformation factors P_α are systematically studied within the cluster-formation model (CFM) for nuclei around Z=82, N=126 closed shells. The calculations show that the P_α calculated by CFM is linearly dependent on the product of valance protons (holes) and valance neutrons (holes) N_p N_n. It is consistent with our previous works[SUN X D, et al. Phys Rev C, 2016, 94 (2):024338; DENG J G, et al. Phys Rev C, 2017, 96 (2):024318], which P_α are model-dependent and extracted from the ratios of calculated α decay half-lives to experimental data. Combining with our previous works, we confirm that the P_α is linearly dependent on the N_pN_n for nuclei around Z=82, N=126 shell closures. In addition, the valance proton-neutron interaction plays a key role in the α preformation.     

Improved empirical formula for α particle preformation factor

In this contribution,the α preformation factors of 606 nuclei are extracted within the framework of the generalized liquid drop model(GLDM).Through the systematic analysis of the α preformation factors of even-even Po-U isotopes,we found that there is a significant weakening of influence of N=126 shell closure in uranium,which is consistent with the results of a recent experiment [J.Khuyagbaatar et al.,Phys.Rev.Lett.115,242502(2015)],implying that N=126 may not be the magic number for U isotopes.Furthermore,we propose an improved formula with only 7 parameters to calculate α preformation factors suitable for all types of α-decay;it has fewer parameters than the original formula proposed by Zhang et al.[H.F.Zhang et al.,Phys.Rev.C 80,057301(2009)]with higher precision.The standard deviation of the α preformation factors calculated by our formula with extracted values for all 606 nuclei is 0.365 with a factor of 2.3,indicating that our improved formula can accurately reproduce the α preformation factors.Encouraged by this,the α-decay half-lives of actinide elements are predicted,which could be useful in future experiments.Notably,the predicted α-decay half-lives of two new isotopes 220 Np [Z.Y.Zhang,et al.,Phys.Rev.Lett.122,192503(2019)] and 219 Np [H.B.Yang et al.,Phys.Lett.B 777,212(2018)] are in good agreement with the experimental α-decay half-lives.     

α preformation and penetration probability for heavy nuclei

The α preformation factor and penetration probability have been analyzed for even--even nuclei of Po, Rn, Ra using experimental released energies and α decay half-lives in the frame of the double folding model. It is shown that N=126 is a neutron magic number from α preformation and shell effects play an important role in α preformation. The closer the nucleon number is to the magic number, the more difficult α formation in the parent nucleus is. The preformation factor can supply information on the nuclear structure and the penetration probability mainly determines α decay half-life.     

理论预测超重核274-291Cn和266-287Ds的衰变模式

自发裂变和α衰变是影响超重核稳定性的两个主要因素。为了探索270Ds附近的长寿命的超重核,系统地计算了电荷数在104 ≤ Z ≤ 112范围内的α衰变与自发裂变之间的竞争。采用推广的液滴模型和唯象的解析公式计算了α衰变半衰期。基于包括壳效应和同位旋效应的WKB近似方法估算了相同超重核的自发裂变半衰期,进而预测了未知超重核274-276,279Cn与267-269Ds的衰变模式。The stability of superheavy nuclei (SHN) is controlled mainly by spontaneous fission and α decay processes. To investigate whether long lived SHN could really exist around 270Ds, the competition between α decay and spontaneous fission in the region 104 ≤ Z ≤ 112 are studied systematically. The α decay half-lives are investigated by employing a generalized liquid drop model (GLDM) and phenomenological analytical formula. Calculations of spontaneous fission half-lives for the same SHN are carried out based on the Wenzel-Kramers-Brillouin(WKB) approximation with both the shell effect and the isospin effect included. Decay modes are predicted for the unknown nuclei 274-276,279Cn and 267-269Ds.     

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.     

Model-independent trend of α-preformation probability

The α-preformation probability is directly deduced from experimental α decay energies and half-lives in an analytical way without any modified parameters. Several other model-deduced results, are used to compare with that of the present study. The key role played by the shell effects in the α-preformation process is indicated in all these cases. In detail, the α-preformation factors of different theoretical extractions are found to have similar behavior for one given isotopic chain, implying the model-independent varying trend of the preformation probability of α particle. In addition, the formation probability of heavier particle in cluster radioactivity is also obtained, and this confirms the relationship between the cluster preformation factor and the product of the cluster and daughter proton numbers.     

奇Z超重核的禁戒α衰变(英文)

采用密度依赖的结团模型研究了奇Z 超重核的禁戒α衰变, 粒子与子核之间的微观核势通过双折叠模型对M3Y 核子-核子相互作用势以及 粒子与子核的密度积分给出。 粒子与子核之间的库仑相互作用也通过 粒子与子核的电荷密度积分给出。计算发现,由于非零角动量带来的禁戒效应和小的α粒子预形成几率,奇Z 超重核的α衰变寿命会明显变长。We investigate the α-transition of odd-Z superheavy nuclei by the density-dependent cluster model (DDCM). The microscopic nuclear potential between the -particle and the daughter nucleus is evaluated numerically from the double-folding model with the standard M3Y nucleon-nucleon interaction. The Coulomb potential is also obtained from the double-folding integral of the proton-proton Coulomb interaction with the charge density distributions of α-particle and daughter nucleus. From our calculations, enhanced stability againstα-decays is found for the odd-Z superheavy nuclei due to the hindrance effect of non-zero angular momentum and the small preformation factor of the -particle.     

10Be中子谱因子的实验研究

核谱因子描述了单粒子轨道中核子的占有状态,在核结构和核天体物理中有重要的应用。目前国际上10Be中子谱因子的研究结果存在3倍左右的差异。本实验利用中国原子能科学研究院HI-13串列加速器的高灵敏度Q3D磁谱仪,对13C（9Be,10Be）12C反应角分布进行了精确测量。通过实验数据和扭曲波玻恩近似（DWBA）计算结果进行比较,导出了10Be的中子谱因子。该结果与转动不变壳模型理论及曾敏尔等的评价结果基本一致。利用该结果可以得到9Be（n,γ）10Be的天体物理反应率,评价该反应在相关天体环境中对CNO循环种子核12C的影响,为核结构和核天体物理提供可靠数据。Spectroscopic factor describes the overlap between the initial and final states and gives some information on the occupancy of a given single-particle orbiting around nuclear. It plays an important role in a variety of topics on nuclear structure and nuclear astrophysics. Nowadays, several experiments have been performed to study the neutron spectroscopic factor of 10Be, but the results have a big difference with each other. In order to clarify this discrepancy, new measurement is highly needed. In this work, the angular distribution of 13C(9Be,10Be)12C reaction was measured at the Q3D magnetic spectrometer of the HI-13 tandem accelerator, China Institute of Atomic Energy, Beijing. And then, the neutron spectroscopic factor of 10Be was derived by normalizing the calculational differential cross-sections with the distorted-wave Born approximation to the experimental data. The present value is in good agreement with that obtained by Tsang et al. and also in good agreement with that derived from translationary invariant shell model calculation. One can use this result to calculate the 9Be(n, γ)10Be reaction rates and calculate its influence to the production of 12C.     

恒星氦燃烧关键反应12C(α,γ)16O天体物理S因子及其反应率

恒星氦燃烧阶段3α反应和12C（α,γ）16O反应相互竞争,两者的反应率共同决定了氦燃烧结束后12C与16O的丰度比,该比值是大质量恒星后继演化以及伴随的元素核合成过程的初始条件。目前,氦燃烧12C（α,γ）16O反应起始T₉=0.2处,天体物理模型要求的反应率的精确度要低于10%,然而尚未有实验或理论给出满足要求的结果。最为直接和可靠地获取12C（α,γ）16O反应率的方法,就是尽可能往低能区测量其天体物理S因子,然后通过理论外推到感兴趣的能区。为此基于经典的R-矩阵理论,建立了适用于低能核反应的多道、多能级的约化R-矩阵理论来拟合几乎所有可用的16O系统的实验数据。配合使用协方差统计和误差传播理论,拟合外推得到了客观的、内部自恰的和唯一性好的12C（α,γ）16O反应天体物理S因子。总的外推S因子STOT（0.3 MeV）=162.7±7.3 keV·b,理论上首次给出达到恒星演化与元素核合成模型的最低要求的S因子。基于计算给出的全能区的S因子,数值积分给出了温度位于0.04 6 T₉ 6 10的12C（α,γ）16O天体物理反应率。在T₉=0.2处,推荐的反应率为（7.83 ±0.35）×10-15 cm3mol-1s-1。During stellar helium burning, the rates of 3α and the 12C(α,γ)16O reaction, in competition with one another, determine the relative abundances of 12C and 16O in a massive star. The abundance ratio is the beginning condition of the following nucleosynthesis and star evolution of massive stars, which are extremely sensitive to the rate of 12C(α,γ)16O reaction at T₉=0.2. The most direct and trustworthy way to obtain the reaction rate of the 12C(α,γ)16O reaction is to measure the S factor for that reaction to as low energy as possible, and to extrapolate to energies of astrophysical interest. Based on a new multilevel and multichannel reduced R-matrix theory for applications in nuclear astrophysics, we have obtained an accurate and self-consistent astrophysical S factor of 12C(α,γ)16O, by a global fitting for almost all available experimental data of 16O system, with the coordination of covariance statistics and error-propagation theory. The extrapolated S factor of 12C(α,γ)16O was obtained with a recommended value STOT (0.3 MeV)=162.7±7.3 keV·b. And the reaction rates of 12C(α,γ)16O for stellar temperatures between 0.04 6 T₉ 6 10 are provided. At T₉=0.2, the reaction rate is (7.83 ±0.35)×10-15 cm3mol-1s-1, where stellar helium burning occurs.     

α Decay Properties of Even-Even Nuclei~(296-308)120 Within the Two-Potential Approach

In the present work,we predict the α decay half-lives of unknown even-even nuclei ~(296-308)120 within the two-potential approach,whose α decay energy Qa is calculated using WS3+mass model.To reduce the deviations between the predictions and experimental data due to nuclear shell effect,the analytic formula of α decay hindrance factor is introduced to the two-potential approach,whose parameters had been extracted from even-even nuclei in the region of 82 Z 126 and 152 N 184 in our previous work [Deng et al.,Chin.Phys.C 42(2018) 044102].In addition,for comparing,we use a type of α decay general formula Universal Decay Law(UDL) and a semi-empirical formula in the superheavy nucleus(SEMFLS) to calculate the half-lives of even-even nuclei ~(296-308)120.The results indicate that our predicted values and the calculated values of the above two empirical formulas are mutually confirmed.Meanwhile,we systematically study α decay chains of ~(296-308)120 and predict the decay modes for superheavy nuclei to help to identify new superheavy isotopes.     

Effects of shell correction on α decay properties

The shell correction effects on the α decay properties of heavy and superheavy nuclei have been studied in a macroscopic-microscopic manner. The macroscopic part is constructed from the generalized liquid drop model(GLDM), whereas the microscopic part, namely, the shell correction energy, brings about certain effects on the potential barriers and half-lives under a WKB approximation, which is emphasized in this work. The results show that the shell effects play a significant role in the estimation of the α decay half-lives within the actinide region.Predictions of the α decay half-lives are then generated for superheavy nuclei, which will provide useful information for future experiments.     

High-Speed Geometric Quantum Computation with Trapped Thermal Ions via Vibrational Mode Decay

We utilize the general displacement operator proposed recently [C.Y. Chen, et al., Phys. Rev. A 74 （2006） 032328] to investigate a high-speed geometric quantum computation via vibrational mode decay of two trapped thermal ions. We find that, under some special conditions, the geometric phase gating is somewhat faster in the heating case than in the ideal case. We also investigate analytically the influence from the vibrational mode heating on the fidelity and the success probability of the implementation.     

Alpha Decay as a Probe of the Structure of Neutron-deficient Nuclei Around Z =82

In this contribution I would like to review briefly our recent studies on nuclear α formation probabilities in heavy nuclei and their indication on the underlying structure of the nuclei involved. In particular, I will show that the empirical α-formation probabilities, which can be extracted from experimental half-lives, exhibit a rather smooth function with changing proton or neutron numbers. This allows us to distinguish the role played by pairing collectivity in the clustering process. The sudden hindrance of the clustering of the nucleons around the N = 126 shell closure is due to the fact that the configuration space does not allow a proper manifestation of the pairing collectivity. The influence of the Z = 82 shell closure on the α formation properties will also be discussed. Moreover, we have evaluated the α-decay fine structure to excited 0+ states in Hg and Rn isotopes as well as the α-decay from the excited 0+ states in the mother nucleus. It is thus found that the α decay is sensitive to the mixture of configurations corresponding to different nuclear shapes.     

Comment on breakup densities of hot nuclei

In [V.E. Viola et al., Phys. Rev. Lett. 93 (2004) 132701, D.S. Bracken et al., Phys. Rev. C 69 (2004) 034612] the observed decrease in spectral peak energies of IMFs emitted from hot nuclei was interpreted in terms of a breakup density that decreased with increasing excitation energy. Subsequently, Raduta et al. [Ad. Raduta et al., Phys. Lett. B 623 (2005) 43] performed MMM simulations that showed decreasing spectral peaks could be obtained at constant density. In this Letter we point out that this apparent inconsistency is due to a selective comparison of theory and data that overlooks the evolution of the fragment multiplicities as a function of excitation energy.     

α decay properties of ~(297)Og within the two-potential approach

The α decay half-life of the unknown nucleus ~(297)Og is predicted within the two-potential approach, andα preformation probabilities of 64 odd-A nuclei in the region of proton numbers 82 Z 126 and neutron numbers 152 N 184, from ~(251)Cf to ~(295)Og, are extracted. In addition, based on the latest experimental data, a new set of parameters for α preformation probabilities considering the shell effect and proton-neutron interaction are obtained.The predicted α decay half-life of ~(297)Og is 0.16 ms within a factor of 4.97. The predicted spin and parity of the ground states for ~(269)Sg,~(285)Fl and ~(293)Lv are 3/2~+, 3/2~+ and 5/2~+, respectively.     

Experimental study of the validity of quantitative conditions in the quantum adiabatic theorem

The quantum adiabatic theorem plays an important role in quantum mechanics. However, counter-examples were produced recently, indicating that their transition probabilities do not converge as predicted by the adiabatic theorem [K. P. Marzlin et al., Phys. Rev. Lett. 93, 160408 (2004); D. M. Tong et al., Phys. Rev. Lett. 95, 110407 (2005)]. For a special class of Hamiltonians, we examine the standard criterion for adiabatic evolution experimentally and theoretically, as well as three newly suggested adiabatic conditions. We show that the standard criterion is neither sufficient nor necessary.