H F Zhang

Competition between α-decay and spontaneous fission for superheavy nuclei

The α-decay half-lives of recently synthesized superheavy nuclei (SHN) are investigated by employing a unified fission model (UFM) and Royers analytical formula (2000 J. Phys. G: Nucl. Part. Phys. 26 1149). The good agreement with the experimental data indicates the UFM and the analytical formula are useful tools to investigate these α-decays. A modified formula is proposed for determining the spontaneous fission half-lives based on Swiateckis formula, including the microscopic shell correction and isospin effect.The spontaneous fission half-lives for heavy and SHN in regions from Th to Fl are calculated systematically. Experimental data are well reproduced by the modified Swiatecki formula. The competition between α-decay and spontaneous fission is analyzed in detail and the decay modes are predicted for the unknown cases.

Half-lives of cluster radioactivity with a generalized liquid-drop model

Half-lives of cluster radioactivity treated as a very asymmetric spontaneous fission are investigated within the WKB barrier-penetration probability. The potential barrier is constructed using a generalized liquid-drop model (GLDM), taking into account the nuclear proximity energy, the mass asymmetry, an accurate nuclear radius, a phenomenological pairing correction and the microscopic shell corrections. The calculated cluster emission half-lives accurately reproduce the experimental data. Predictions are provided for possible cluster radioactivity within the GLDM using the up-to-date atomic mass table AME2011, which may be used for the future experiments.

Concise methods for proton radioactivity

Concise methods are proposed to study proton radioactivity. The spectroscopic factor is obtained from relativistic mean field (RMF) theory combined with the BCS method (RMF+BCS). The assault frequency is estimated by a quantum mechanical method considering the structure of the parent nucleus. The penetrability is calculated by the WKB approximation. No additional parameters are introduced. The extracted experimental spectroscopic factors are compared with those from the calculations by the RMF+BCS, and the agreement is good, implying that the present methods work quite well for proton radioactivity. Predictions are provided for some most possible proton emissions, which may be useful for future experiments.

Influence of hexadecapole deformation on production cross sections of superheavy nuclei

The current heaviest superheavy nuclei (SHN) are experimentally synthesized by using Ca-48 to bombard actinide nuclei via fusion reactions. Actinide nuclei often have considerable hexadecapole deformation in addition to quadrupole deformation, which was not considered in previous theoretical studies. With the dinuclear system concept, and by taking the hexadecapole deformation in to consideration in addition to the quadrupole deformation, the hot fusion probability leading to the synthesis of SHN is investigated systematically. Synthesis of superheavy elements (296)118 and (295)118 by using the Ca-48+ Cf-251 reaction channel is evaluated and discussed, and the maximal evaporation residue cross sections (ERCSs) of the 3n and 4n channels are predicted to be 1.90 and 0.11 pb, respectively. The predicted maximum ERCSs in 3n and 4n evaporation channels of the Bk-249(Ti-50, xn)(299-x)119 reaction are 0.12 and 0.04 pb, respectively. The most favorable reaction to synthesize the element Z = 120 turns out to be Cf-251(Ti-50, xn) (301-x)120, but the predicted maximum cross section for this reaction is only 67 fb. Therefore, superheavy element 119 may be the most hopeful new element for Z > 118 to be synthesized under some improved experimental conditions in the near future.

α decay half-lives for Z = 108,114,120,126 isotopes and N = 162,184 isotones

Within the generalized liquid drop model (GLDM) including the proximity effects between nuclei in the neck and the gap between the nascent fragments, the α decay half-lives of the 108, 114, 120, 126 isotopes and 162, 184 isotones are investigated in the quasi-molecular shape path. The Qα is obtained from the macroscopic–microscopic method (MMM) or from the experimental data. The calculated results are compared with experimental data, and both reveal that 270Hs is a double magic nucleus. The correct agreement allows us to make predictions for the α decay half-lives of other still-unknown superheavy nuclei(SHN) in the same framework. It is concluded that 298114 may be a double magic nucleus and N = 184 the neutron magic number for Z = 120 and Z = 126, however, further experimental evidence is needed.

Competition between α-decay and proton radioactivity within a generalized liquid drop model

The α-decay and proton radioactivity half-lives of a number of spherical nuclei in the proton range Z = 51–83 were investigated within a generalized liquid drop model (GLDM), including the proximity effects between nuclei in a neck and the mass and charge asymmetry. The penetrability on potential barrier constructed by the GLDM is calculated by the WKB approximation for the two decay modes. The spectroscopic factors (Sp) evaluated by the relativistic mean field theory combined with the BCS method for the proton radioactivity. The agreement between theoretical results and experimental data is satisfactory for both α and proton emission, which allows us to make predictions about the half-lives of the two decay modes for some unstable nuclei in the same theoretical framework.