Analytic expressions for alpha particle preformation in heavy nuclei

Experimental alpha decay energies and half-lives are investigated systematically to extract alpha particle preformation in heavy nuclei. Formulas for the preformation factors are proposed that can be used to guide microscopic studies on preformation factors and perform accurate calculations of the alpha decay half-lives. There is little evidence for the existence of an island of long stability of superheavy nuclei.

alpha-decay half-lives of superheavy nuclei and general predictions

The generalized liquid drop model (GLDM) and the cluster model have been employed to calculate the alpha-decay half-lives of superheavy nuclei (SHN) using the experimental alpha-decay Q values. The results of the cluster model are slightly poorer than those from the GLDM if experimental Q values are used. The prediction powers of these two models with theoretical Q values from Audi et al. (Q(Audi)) and Muntian et al. (Q(M)) have been tested to find that the cluster model with Q(Audi) and Q(M) could provide reliable results for Z > 112 but the GLDM with Q(Audi) for Z <= 112. The half-lives of some still unknown nuclei are predicted by these two models and these results may be useful for future experimental assignment and identification.

Alpha decay half-lives of heavy nuclei within a generalized liquid drop model

Theoretical alpha-decay half-lives of the heaviest nuclei are calculated using the experimental Q value. The barriers in the quasi-molecular shape path is determined within a Generalized Liquid Drop Model (GLDM) and the WKB approximation is used. The results are compared with calculations using the Density-Dependent, M3Y (DDM3Y) effective interaction and the Viola-Seaborg-Sobiczewski (VSS) formulae. The calculations provide consistent estimates for the half-lives of the a decay chains of these superheavy elements. The experimental data stand between the GLDM calculations and VSS ones in the most time.

Half-Lives of Superheavy Nuclei in Z=113 Alpha Decay Chain

The generalized liquid drop model (GLDM), including the proximity effects and centrifugal potential, and the cluster model with Cosh potential are used to study the half-lives of some Z=113 isotopes and their alpha-decay products.The experimental half-lives of (284)113, (283)113, (282)113and their alpha-decay products are well reproduced by the two models when zero angular momenta transfer is assumed. For (278)113 and its alpha-decay products, both the GLDM andthe cluster model could provide satisfactory results if we assume the alpha particle carry five units of angular momenta, which indicates that possible non zero angular momenta transfer and need further experimental measurements with high precision. Finally, we show that half-lives of alpha-decay are quite sensitive to the angular momentum transfers, and a formula could be used to describe the correlation between alpha-decay half-life and angular momentum transfer successfully.

Influence of in-medium nucleon-nucleon cross section on the isoscaling parameter alpha

The influence of in-medium nucleon-nucleon cross section on the isoscaling parameter a is investigated for two couples of central nuclear reactions Ca-40 + Ca-40 and Ca-60 + Ca-40; Sn-112 + Sn-112 and Sn-124 + Sn-124 within the isospin dependent quantum molecular dynamics. The calculated result shows that the influence of the in-medium nucleon-nucleon cross section on the isoscaling parameter a is mainly determined by the corresponding number of collisions, both for isospin dependent and isospin independent parameterizations. The mechanisms behind the effects of the in-medium nucleon-nucleon cross sections on the alpha are investigated in more details.

Alpha decay energies and half-lives for possibly synthesized superheavy elements

We investigate the ground state properties of some superheavy nuclei, which may be synthesized in future experiments. Special emphases are placed on the alpha decay energies and half-lives. The alpha decay energies and half-lives from different theoretical models are compared and discussed comprehensively. Through these calculations and comparisons, the optimal superheavy elements to be synthesized in future experiments are proposed theoretically.

Systematic study on alpha decay half-lives of superheavy nuclei

The a-decay half-lives of a set of superheavy nuclear isotope chain from Z = 105 to 120 have been analyzed systematically within the WKB method, and some nuclear structure features are found. The decay barriers have been determined in the quasi-molecular shape path within the Generalized Liquid Drop Model (GLDM) including the proximity effects between nucleons in a neck and the mass and charge asymmetry. The results are in reasonable agreement with the published experimental data for the alpha decay half-lives of isotopes of charge 112, 114, and 116, of the element 294118 and of some decay products. A comparison of present calculations with the results by the DDM3Y effective interaction and by the Viola-Seaborg Sobiczewski (VSS) formulae is also made. The experimental a decay half lives all stand in between the GLDM calculations and VSS formula results. This demonstrates the possibility of these models to provide reasonable estimates for the half-lives of nuclear decays by a emissions for the domain of SHN. The half-lives of these new nuclei are thus well tested from the reasonable consistence of the macroscopic, the microscopic, the empirical formulae and the experimental data. This also shows that the present data of SHN themselves are consistent. It could suggest that the present experimental claims on the existence of new elements Z = 110 similar to 118 are reliable. It is expected that greater deviations of a few SHN between the data and the model may be eliminated by further improvements on the precision of the measurements.

Color center formation in alpha-Al2O3 induced by high energy heavy ions

Single crystals of alpha-alumina were irradiated at room temperature with 1.157 (GeVFe)-Fe-56, 1.755 (GeVXe)-Xe-136 and 2.636 (GeVU)-U-238 ions to fluences range from 8.7 x 10(9) to 6 x 10(12) ions/cm(2). Virgin and irradiated samples were investigated by ultraviolet visible absorption measurements. The investigation reveals the presence of various color centers (F, F+, F-2(2+), F-2(+) and F-2 centers) appearing in the irradiated samples. It is found that the ratio of peak absorbance of F-2 to F centers increases with the increase of the atomic numbers of the incident ions from Fe, Xe to U ions, so do the absorbance ratio of F-2(2+) to F+ centers and of large defect cluster to F centers, indicating that larger defect clusters are preferred to be produced under heavier ion irradiation. Largest color center production cross-section was found for the U ion irradiation. The number density of single anion vacancy scales better with the energy deposition through processes of nuclear stopping, indicating that the nuclear energy loss processes determines the production of F-type defects in heavy ion irradiated alpha-alumina.

alpha decay half-lives of new superheavy nuclei within a generalized liquid drop model

The alpha decay half-lives of the recently produced isotopes of the 112, 114, 116 and 118 nuclei and decay products have been calculated in the quasi-molecular shape path using the experimental Q(alpha) value and a Generalized Liquid Drop Model including the proximity effects between nucleons in the neck or the gap between the nascent fragments. Reasonable estimates are obtained for the observed alpha decay half-lives. The results are compared with calculations using the Density-Dependent M3Y effective interaction and the Viola-Seaborg-Sobiczewski formulae. Generalized Liquid Drop Model predictions are provided for the alpha decay half-lives of other superheavy nuclei using the Finite Range Droplet Model Q(alpha) and compared with the values derived from the VSS formulae.

Alpha decay half-lives of new superheavy elements through quasimolecular shapes

The lifetimes of alpha decays of the recently produced isotopes of the elements 112, 114, 116 and the element (294)118 and of some decay products have been calculated theoretically within the Wentzel-Kramers-Brillouin approximation. The alpha decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimated for the observed alpha decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T-1/2 values as long as one uses a correct alpha decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.

Properties of the superheavy nuclei (288)115 and its alpha-decay chain in a generalized liquid-drop model

The properties of the nuclei belonging to the newly observed nuclei starting from (288)115 have been studied with the generalized liquid drop model connected with WKB approximation. The calculated results have been compared with the results of the DDM3Y theory and the experimental data. The half lives of this new alpha decay chain have been well tested from the consistence of the macroscopic, microscopic and the experimental data.

Medium effect of nucleon-nucleon cross section on the isoscaling parameter alpha

The medium effect of in-medium nucleon-nucleon cross section sigma(med)(NN) (alpha(m)) on the isoscaling parameter a is investigated for two couples of central nuclear reactions Ca-40 + Ca-48 and Ca-60 + Ca-48; Sn-112 + Sn-112 and Sn-124 + Sn-124 at beam energy region from 40 to 60 MeV/nucleon with isospin dependent quantum molecular dynamics. It is found that there is the obvious medium effect of sigma(med)(NN) (alpha(m)) on the isoscaling parameters alpha. The mechanism for the medium effect of sigma(med)(NN) (alpha(m)) on a is investigated.

Properties of alpha-decay to ground and excited states of heavy nuclei

Branching ratios and half-lives of alpha-decay to the ground-state rotational bands as well as the high-lying excited states of even-even nuclei have been calculated in the framework of the generalized liquid drop model (GLDM) and Royer's formula that we improved very recently. The calculation covers the isotopic chains from Ra to No in the mass regions 222 <= A <= 252 and 88 <= Z <= 102. The agreement between the calculated results and the experimental data indicates the reliability of investigating the properties of the unfavored alpha-decay with our method, especially the improved Royer's formula, which is very valuable for the analysis of experimental data. In addition, the dependence of half-lives on excitation energies of daughter nuclei has been investigated. It is shown that the influence on half-lives becomes stronger and stronger with the increase of the excitation energies.

Fine structure of alpha decay to rotational states of heavy nuclei

To gain a better insight into alpha-decay fine structure, we calculate the relative intensities of alpha decay to 2(+) and 4(+) rotational states in the framework of the generalized liquid drop model (GLDM) and improved Royer's formula. The calculated relative intensities of a decay to 2(+) states are in good agreement with the experimental data. For the relative intensities of alpha decay to 4(+) states, a good agreement with experimental data is achieved for Th and U isotopes. The formula we obtain is useful for the analysis of experimental data of alpha-decay fine structure. In addition, some predicted relative intensities which are still not measured are provided for future experiments.