α decay energies and half-lives from a macroscopic-microscopic model

α decay energies of 323 heavy nuclei with Z≥82 are evaluated with a macroscopic-microscopic model.In this model,the macroscopic part is treated by the continuous medium model and the microscopic part consists of shell and pairing corrections based on the Nilsson potential.α decay half-lives are calculated by Viola-Seaborg formula.The results of α decay energies and half-lives are compared with experimental values and satisfactory agreement is found.The recoiling effect of the daughter nucleus on α decay half-life is also discussed.     

在超重核区应用Viola-Seaborg公式研究α衰变寿命

在超重核区(Z≥104)使用文献[7—9]给出的3组参数应用Viola-Seaborg公式计算了α衰变寿命,所得结果与实验值进行比较,发现其结果与实验值相差较大。为此,利用最小二乘法分别在重核区和超重核区重新对参数进行了拟合,得到的计算结果与实验值相比符合得较理想,尤其是由超重核得到的参数的结果非常理想。     

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.     

在超重核区应用Viola Seaborg公式研究α衰变寿

在超重核区（Z≥104）使用文献[7—9]给出的3组参数应用Viola Seaborg公式计算了α衰变寿命, 所得结果与实验值进行比较, 发现其结果与实验值相差较大。 为此, 利用最小二乘法分别在重核区和超重核区重新对参数进行了拟合, 得到的计算结果与实验值相比符合得较理想, 尤其是由超重核得到的参数的结果非常理想。The α decay half lives of the super heavy nuclei in the mass region （Z≥104） were calculated by Viola Seaborg formula with three sets of parameters. The calculated results show that all the three sets of parameters caused rather large deviations from the experimental data. To solve this problem, we have done a parameter fitting in the regions of heavy nuclei and super heavy nuclei respectively, with the least squares method. With the new sets of parameters, the calculated α decay half lives are in much better agreement with the experimental data. In particular, the results calculated with the new parameters in the region of super heavy nuclei are even better.     

A CALCULATION OF ISOSPIN DEPENDENT LEVEL WIDTH IN COMPOUND NUCLEUS 30P

Whether the degree of freedom of isospin states in highly excited compound nucleus is conservative or not gives the information of Coulomb interaction which affects the decay property of compound nucleus.The isospin dependent level decay widths of ³⁰P are calculated by means of H.A.Weidenmuller's statistical theory.It takes the isospin coupling coefficients into account for transmission coefficients as well as for the total number of decay channels.This is the difference from that of Hauser-Feshbach formula.     

PATH INTEGRAL CALCULATION OF QUANTUM TUNNELING FOR CUBIC POTENTIAL AT FINITE TEMPERATURE

The periodic instanton method is used to study the decay rates of metastable ground state and excited states of the cubic potential. The imaginary part of the energy is calculated through the standard procedure in the path-integral scheme. A formula of the decay rate valid for the entire region of energy is obtained. This formula provides a linkage between classical thermal activation at high temperatures and purely quantum tunneling at zero temperature. It is shown that in the low energy limit this more general result reduces exactly to the vacuum result. The temperature dependence of the decay rate agrees with earlier works in the literature.     

用推广的Viola-Seaborg公式计算α衰变寿命

根据Audi等编评的最新核数据表, 对Z≥84, N≥128的核的α衰变实验寿命用Viola-Seaborg公式进行最小方差拟合, 得到一套新参数. 用新拟合参数计算的偶偶核的衰变寿命与实验寿命很好地符合, 平均偏差1.3倍.而对奇A和奇奇核理论寿命与实验寿命相差较远. 考虑到处于基态时奇A和奇奇核与偶偶核的主要区别在于自旋和宇称, 对Viola-Seaborg公式做了推广. 在公式中引入了离心势垒(即α粒子轨道角动量)对衰变寿命的影响. 由推广公式计算的奇A和奇奇核的寿命与实验寿命平均偏差2.5倍,最大偏差5—6倍.     

有效液滴模型对超铅区结团放射性的研究

利用有效液滴模型计算了超铅区结团放射半衰期.在计算Gamow势垒穿透因子时采用了碎块体积不守恒以及有效惯性系数因子,并用有效的核半径常数公式代替原来的经验公式.理论计算得到的结团放射半衰期和实验值符合得很好,其半衰期对数值的均方差只有0.895.理论结果表明,有效液滴模型能充分反映N=126和Z=82的壳效应,并且在奇数结团25Ne,29Mg中出现了明显的奇偶质量摆动现象.另外,理论计算得到的结团半衰期基本符合盖革-努塔尔定律,并基于理论结果得到了一些关于盖革-努塔尔定律的有意义的结论.     

Perturbation analysis of an energy-balance model: time constants oflow-current cascade arcs in argon

A time-constant formula is derived from a perturbation analysis of an equilibrium energy-balance equation of arc plasmas. The formula gives the time constant associated with changes in arc quantities when the arc current is perturbed from its steady-state. The current perturbation is assumed to be very small and the mathematical approach assumes that the arc behavior is linear. This paper investigates how well a linear model describes the small-signal behavior of the arc. The derived formula gives an insight into which are properties are responsible for the dynamic behavior of the arc about its steady-state operating point. Application of the method has been illustrated with arcs in argon. Results calculated with the formula are compared to time-constants deduced from equilibrium model predictions of the decay in the electric field when the current is stepped     

General equation for Zeno-like effects in spontaneous exponential decay

Different perturbation mechanisms of the spontaneous decay constant are shown: the inelastic interaction of emitted particles with particle detector, decay onto an unstable level, Rabi transition from the final state of decay (electromagnetic field domination) and some others are really the special kinds of one general effect – the perturbation of the decay constant by dissipation of the final state of decay. Such phenomena are considered to be Zeno-like effects and the general formula for the perturbed decay constant is deduced.     

Inclusive semileptonic decays of B mesons

The probability of inclusive semileptonic decay of B mesons is calculated in the constituent-quark model. A compact formula is obtained for the differential decay width of a B meson in terms of the corresponding decay width of a free b quark and the wave function of the internal motion of the quarks in the B meson. Numerical values of semileptonic-decay widths are obtained for a series of models of the wave function. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 734–737 (25 May 1997)     

Analysis of the total activation cross section of all possible reactions producing the same radioactive nuclide for the same element

Firstly,according to the regulation of growth and decay of radioactive nuclides produced in reactions,a formula used to calculate the total activation cross section of all possible reactions producing the same radioactive nuclide for the same element is deduced,and it is pointed out that the activation formula given in two references is incorrect.Then,as an example,the so-called total activation cross section in one of the two references is analyzed and the correct results of the cross sections of 182W(n,p)182(m+g)Ta,183W(n,p)183Ta and 206Pb(n,a)203Hg induced by neutrons around 14 MeV calculated with the data given in the literature,the nuclear parameters and some evaluated values are given.Finally,the correct results are compared with other values collected in the literature.     

Half-Lives for Alpha Radioactivity of Elements with 104 ≤ Z ≤ 120 within Unified Fission Model

α decay half-lives are calculated using the Qα values obtained by Semi-empirical Shell Model in the framework of the Unified Fission Model (UFM) with the Coulomb repulsion, nuclear attraction due to proximity potential, and rotational energy due to angular momentum transfer of α particle. In addition, the calculated and experimental half-lives of 425 nuclei are compared to check the validity of the model applied on α decay. The calculated half-lives of α decay are in good agreement with the experimental data. Finally, some usefulpredications on the α decay half-lives are provided for future experiments.     

Effect of intrinsic degrees of freedom on the quantum tunneling of a collective variable

The effect of intrinsic degrees of freedom on tunneling through a potential barrier is discussed using a BKW-like approximation. In the present work intrinsic degrees of freedom are represented by a single harmonic oscillator. The theory leads to a formula for the effect of the coupling on the decay width Γ of a metastable state. When the frequency ω of the intrinsic degree of freedom is large, then Γ → Γ_ad where Γ_ad is the decay width calculated with the adiabatic barrier. An inequality Γ ≤ Γ_ad is proved for any form of the coupling hamitonian. Corrections are discussed and are shown to be of order $\text{1}\text{M}$ where M is the mass of the tunneling coordinate. An application to fission is considered. The generalization of our formula for Γ to the case of many intrinsic degrees of freedom is given explicitly.     

Empirical formulas for proton decay half-lives:Role of nuclear deformation and Q-value

Two empirical formulas for the proton decay half-lives including nuclear deformation are proposed. The formula with parameter set I gives the logarithm of the proton decay half-lives as an explicit function of the orbital angular momentum with eight adjustable parameters, whereas that with set II represents the logarithm of the reduced half-lives as an implicit function of the angular momentum with seven adjustable parameters. Experimental data for the half-lives of 44 proton emitters in the ground state or isomeric state were used to obtain the parameters. The experimental and calculated Q values were used. Different sets of parameters were obtained for the ground state transition, isomeric state transition, and all transitions for both deformed and spherical nuclei. The best agreement with experimental data was observed for set I for deformed proton emitters with experimental Q values.     

On the decay of θ mesons in charmonium models

We derive a new formula for the decay rate of the ψ mesons by properly treating the dependence of lowest order electromagnetic annihilation on the quark-antiquark bound state wave function. Results are presented for currently used non-relativistic potentials models for charmonium. In all cases substantial corrections to previous estimates from commonly used formulas occur. Our results are of relevance also for hadronic decay via gluons in QCD and weak decay of pseudoscalar mesons.     

Application of the theory of open quantum systems to nuclear physics problems

Quantum diffusion equations with transport coefficients explicitly depending on time are derived from the generalized non-Markovian Langevin equations. The asymptotic behavior of the friction and diffusion coefficients is investigated in the case of the FC and RWA couplings between the collective and internal subsystems. An asymptotic expression is obtained for the propagator of the density matrix of the open quantum system with the general quadratic Hamiltonian, linearly coupled (in coordinate and momentum) to internal degrees of freedom. The effect of different sets of transport coefficients on the decoherence and decay rate of the metastable state is investigated using the master equation for the reduced density matrix of open quantum systems. The developed approach is used to study the capture of the projectile nucleus by the target nucleus at energies near the Coulomb barrier. Capture cross sections in asymmetric reactions are well described with allowance for the calculated capture probabilities. Particular cases where dissipation favors penetration through the potential barrier are found. The generalized Kramers formula for the quasi-stationary decay rate of the quantum metastable systems is analytically derived.     

气相爆轰波沿胞格的动力学机理研究

 建立了一种以子单元分析为基础,研究气相爆轰波沿胞格运动时的动力学机理的新方法。根据该子单元的性质和斜冲击波关系,首先推导了对撞前后前导冲击波沿胞格对称轴的马赫数之比和入射冲击波入射角及胞格几何性质的关系,求解了胞格结构中的三波点对撞问题。然后,采用爆炸波模拟前导冲击波的自持运动过程,求解气相爆轰波沿胞格的动力学过程,理论分析表明,气相爆轰波在胞格起点首先经历一个增长过程,然后才出现衰减。理论分析结果与实验和数值计算结果的比较表明符合得较好。     

Radiative weak decay of baryons within the Bethe-Salpeter formalism

The Nishijima-Mandelstam formula for the transition amplitude of radiative weak decay of baryons is derived within the Bethe-Salpeter formalism in a manner parallel to the Lehmann-Synanzik-Zimmermann reduction procedure. Feynaman rules for bound quarks are discussed. Employing a Gaussian Bethe-Salpeter amplitude for baryons used by other authors, the transition amplitude for ⁺ p has been calculated. Due to the use of a phenomenological Bethe-Salpeter wave function, the resulting amplitude turns out to be non-gauge invariant. Gauge invariance is imposed by hand and the asymmetry parameter calculated. Normalization of the decay amplitude and calculation of the absolute rate is not attempted. Two serious problems remain in this calculation: First, the lack of gauge invariance, and, second, the calculated amplitudes turn out to be complex.