Revealing the Nature of yrast States in Neutron-Rich Polonium Isotopes

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Abstract
Polonium isotopes having two protons above the shell closure at Z = 82 show a wide variety of low-lying, high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to Po 210 ( N = 126 ) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only selective techniques can be used for their production. We report on the first fast-timing measurements of yrast states up to the 8 + level in Po 214 , 216 , 218 isotopes produced in the β − decay of Bi 214 , 216 , 218 at ISOLDE, CERN. In particular, our new half-life value of 607(14) ps for the 8 1 + state in Po 214 is nearly 20 times shorter than the value available in the literature and comparable with the newly measured half-lives of 409(16) and 628(25) ps for the corresponding 8 1 + states in Po 216 , 218 , respectively. The measured B ( E 2 ; 8 1 + → 6 1 + ) transition probability values follow an increasing trend relative to isotope mass, reaching a maximum for Po 216 . The increase contradicts the previous claims of isomerism for the 8 + yrast states in neutron-rich Po 214 and beyond. Together with the other measured yrast transitions, the B ( E 2 ) values provide a crucial test of the different theoretical approaches describing the underlying configurations of the yrast band. The new experimental results are compared to shell-model calculations using the KHPE and H208 effective interactions and their pairing-modified versions, showing an increase in configuration mixing when moving toward the heavier isotopes.
Funding Information
  • Institutul de Fizică Atomică (PN 23 21 01 02)
  • Agentúra na Podporu Výskumu a Vývoja (APVV-22-0282)
  • Vedecká Grantová Agentúra MŠVVaŠ SR a SAV (1/0651/21)
  • Fonds Wetenschappelijk Onderzoek
  • KU Leuven (C14/22/104)
  • Fonds De La Recherche Scientifique - FNRS (EOS 40007501)
  • Agencia Estatal de Investigación (RTI2018-098868-B-I00, PID2021-126998OB-I00)
  • Research Council of Finland (354968)
  • Bundesministerium für Forschung, Technologie und Raumfahrt (05P21PKCI1)
  • Science and Technology Facilities Council (ST/P004598/1, ST/V001027/1)

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