In-beam gamma-ray and electron spectroscopy of ${}^{249,251}$Md

Abstract

The odd-$Z$ ${}^{251}$Md nucleus was studied using combined $\gamma$-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the $[521]1/2^{-}$ configuration, another rotational structure has been identified using $\gamma$-$\gamma$ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a $[514]7/2^{-}$ single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of $\simeq$ 60% was well reproduced by simulating a set of unresolved excited bands. Moreover, a detailed analysis of the intensity profile as a function of the angular momentum provided a method for deriving the orbital gyromagnetic factor, namely $g_K=0.69_{-0.16}^{+0.19}$ for the ground-state band. The odd-$Z$ ${}^{249}$Md was studied using $\gamma$-ray in-beam spectroscopy. Evidence for octupole correlations resulting from the mixing of the $\Delta l=\Delta j=3$ $[521]3/2^{-}$ and $[633]7/2^{+}$ Nilsson orbitals were found in both ${}^{249,251}$Md. A surprising similarity of the ${}^{251}$Md ground-state band transition energies with those of the excited band of ${}^{255}$Lr has been discussed in terms of identical bands. Skyrme-Hartree-Fock-Bogoliubov calculations were performed to investigate the origin of the similarities between these bands.