Combined in-beam electron andγ-ray spectroscopy ofHg184,186

Abstract

By exploiting the SAGE spectrometer a simultaneous measurement of conversion electrons and γ rays emitted in the de-excitation of excited levels in the neutron-deficient nuclei 184,186 Hg was performed. The light Hg isotopes under investigation were produced using the 4n channels of the fusion-evaporation reactions of 40 Introduction. The neutron midshell Hg and Pb nuclei are some of the most interesting nuclei found in the nuclear landscape. In these nuclei evidence is found that indicates almost degenerate coexisting shapes at low excitation energies [1,2]. For 186 Pb, besides the 0 + ground state the first two excited states are 0 + states [3]. In the corresponding Hg isotopes, besides the ground-state band, a second band with a bandhead at low excitation energy is observed. Meanfield approaches produce different minima in the potential energy surface [4][5][6][7], leading to an identification of these structures as being deformed with one particular macroscopic nuclear shape. In the Pb isotopes these minima are found at deformation values corresponding to spherical, weakly oblate, and prolate shapes. In the light Hg isotopes two distinct minima are associated with weakly oblate and prolate deformation. Based on considerations of the moment of inertia it is proposed that ground-state and low-spin yrast states are members of the weakly oblate deformed band, while the first excited 0 + state is the bandhead of the well-deformed prolate band. In a simple intruder picture the underlying microscopic proton configurations are a π (0p-2h) two-hole structure (weakly oblate) and a π (2p-4h) two-particle-fourhole structure (prolate) [8], respectively. The bandhead energy of the intruding, prolate π (2p-4h) structure approaches the ground state given by the bandhead of the oblate π (0p-2h) band near neutron midshell at N = 104. Furthermore, the energy differences between the individual states of the two bands is lower for the prolate deformed band. Consequently, when approaching midshell the spin of the state for which the prolate band starts forming the yrast band lowers.The combined spectroscopic study of decay γ rays and electrons offers an opportunity to gain a more detailed picture of the interplay between the oblate and prolate bands. A

In-beam conversion-electron spectroscopy of180Hg

“…The recent commissioning of the Silicon and Germanium (SAGE) spectrometer at Jyväskylä offers the prospect of simultaneously measuring with good efficiency both γ rays and conversion electrons in in-beam studies [33]. Indeed, preliminary experiments to study shape coexistence in 182,184 Hg using this device have already been performed [34].…”

Nuclear shape coexistence: A study of the even-even Hg isotopes using the interacting boson model with configuration mixing

“…[131][132][133]). Except for mass A=184 (new results on E0 transitions from conversion electron and γ-ray studies [134]), no new results have been obtained since the most recent NDS evaluations, as cited before.…”

Nuclear shape coexistence in Po isotopes: An interacting boson model study

“…An application to the Pb region was carried out by Barrett et al [133]. The data obtained recently [134][135][136][137][138][139][140] from detailed studies of the Hg nuclei on energy spectra and electric quadrupole properties [B(E2) values, Q moments], however, do indicate that the more simple idea of I spin is not holding so well.…”