Conversion electron spectroscopy and its role in identifying shape coexisting structures in nuclei viaE0 transitions

Abstract

We present, from a historical perspective, the evolution of instruments and techniques developed by our group, in conjunction with other collaborators, to establish a program in conversion electron spectroscopy that could be routinely implemented in radioactive decay studies. We focus here mainly on the investigations that bear upon the study of nuclear shape coexistence and its relation to electric monopole (E0) transitions. We show that many I π →I π (I≠0) transitions in both even and odd nuclei with mixed shape-coexisting configurations have large E0 components accompanying their M1+E2 strength (in some cases nearly pure E0), and that this E0 enhancement is a clear 'signature' for nuclear shape coexistence.

Shape Coexistence in Even–Even Nuclei: A Theoretical Overview

“…Strong electric monopole transitions, characterized by the monopole strength ρ 2 (E0), connecting excited 0 + states to the ground state, are an important signature of SC [491], since they provide a clear sign of shape mixing. The relevant data have been reviewed in [526,527], while novel experimental approaches for their identification, based on conversion electron spectroscopy, have been reviewed by Zganjar [528].…”

De-excitation of the strongly coupled band in Au177 and implications for core intruder configurations in the light Hg isotopes

“…Although a tentative 11/2 − assignment is proposed for the band head of the strongly coupled band in Fig. 2 [6,7]by conversion-electron-γ -ray coincidence measurements [29]. In these isotopes, the deformed 11/2 − and 13/2 − states decay predominantly to the near-spherical 11/2 − member of the 1h 11/2 ⊗ A+1 Hg(0 + 1 ) proton-hole configuration.…”

New systematic features in the neutron-deficient Au isotopes

“…The challenge in studying decay schemes in odd-mass nuclei in this mass region is the widely occurring feature of excited states at very low excitation energy (< 50 keV). This has been handled variously with ultra-low energy singles conversion-electron spectroscopy [42,43] and with low-energy conversion-electron-γ-ray coincidence spectroscopy [8,13,14,44]. We attacked this problem in 183 Au [32] using the large number of deexcitation paths of the 1682.30 keV state, strongly populated in β decay (see above), combined with γ-ray spectroscopy employing, in part, the high-energy precision available using a BEGe detector operated at high gain (27 eV/ch).…”

“…A more limited study of the decays of 185 Hg m g , to 185 Au was also carried out [12,13]. These studies involved measurements of conversion electrons using e-γ coincidences and identification of electric monopole transitions (E0), which provide a modelindependent fingerprint of shape coexistence [14,15]. However, a full understanding of the detailed structure was lacking.…”