abstract

The bandhead of most chiral bands are isomers with a large Weisskopf hindrance factor. Such isomers are proposed as a type of \(K\) isomer. From the data available for the mass region \(A\backsim 80, 100, 130\), and 190, it has been observed that the low value of reduced hindrance factors could be indicative of triaxial shape and orthogonally coupling of the valence nucleon angular momentum at the chiral bandhead.

abstract

Lorentz scalar and mass interactions are studied in more detail in the framework of a reduced Dirac equation for heavy quark–antiquark mesons. A microscopic model for these interactions is proposed and analyzed. The charmonium mass spectrum is reproduced by means of two free parameters; a third parameter is fixed by means of a phenomenological hypothesis in accordance with the model.

abstract

Large-scale shell model calculations are performed within the model spaces sd, zbme and psdpf, to study the positive- and negative-parity energy levels and electromagnetic transitions in the exotic \(^{20-23}\)Mg isotopes. Core-polarization effects on reduced transition probability are introduced through the first-order perturbation theory, which allows for higher energy configurations through excitations of nucleons from core orbits to that outside model space up to \(9\hbar w\). The core-polarization effects have improved the agreement of \(B\)(E2) with their corresponding experimental data, and have an ignorable effect on \(B\)(M1) and \(B\)(E1).

abstract

The correlations of the reduced hindrance factor \(F_{\nu }\) of the \(K\)-isomers in Ta and Hf isotopes with respect to \(N_{p}N_{n}\) (the product of valence nucleons), \(E_{K}-E_{R}\) (the isomer excitation energy referred to a rigid rotor), and \(E_{K}(N_{n})-E_{K}(N_{n-\max })\) (the energy difference between the same configuration at \(N_{n}\) and \(N_{n-\max }\) (middle of a shell), at given spin and isotopic chain) have been re-examined. The analysis is performed in the valence regions divided into particle–particle (\(p\)–\(p\)), particle–hole (\(p\)–\(h\)), and hole–hole (\(h\)–\(h\)) regions, based on the \(N_{p}N_{n}\) phenomenology. The Ta and Hf isotopes are considered, given the availability of the same spin configuration in the different sectors of the valence regions. In our study, we observe that the parameter \(E_{K}(N_{n})-E_{K}(N_{n-\max })\) shows a significant correlation with \(F_{\nu }\), within an isotopic chain.