γ-ray spectroscopy of low-lying excited states and shape competition inOs194

Abstract

The properties of excited states in the neutron-rich nucleus 194 Os have been investigated using the 192 Os( 18 O , 16 O) 194 Os reaction with an 80 MeV beam provided by the IFIN-HH Laboratory, Bucharest. Discrete γ -ray decays from excited states have been measured using the hybrid HPGe-LaBr 3 (Ce) array RoSPHERE. The current work identifies a number of previously unreported low-lying nonyrast states in 194 Os as well as the first measurement of the half-life of the yrast 2 + state of 302( 50) ps. This is equivalent to a B(E2 : 2 + → 0 + ) = 45( 16) W.u. and intrinsic quadrupole deformation of β eff = 0.14(1). The experimental results are compared with Hartree-Fock-Bogoliubov-interacting-boson-model calculations and are consistent with a reduction in a quadrupole collectivity in Os isotopes with increasing neutron number.

Revisiting Grodzins systematics of B(E2) values

“…B(E2)↑ data, fits and experimental result of T. Daniel et al[18] for Os. l u a t e d R a m a n H a b s A l l m o n d…”

“…Thus extrapolations of B(E2) values across the whole nuclear chart cannot be made. The fits for Z=12, 14,18,22,24,26,28,30,32,34,36,48,52,54,74,76,80, 84 and 86 isotopes are marginal, which can probably be understood as varying degrees of collectivity in these nuclides. It is surprising that fits for Z=28 isotopes are remarkably good, even though it is a closed shell.…”

“…. The recent measurement by T. Daniel et al[18] indicates T 1/2 =302(50) ps for the first 2 + state at 218.51 keV in 194 Os. This value gives B(E2)↑ = 1.5( +3 −2 ) e 2 b 2 which is in a perfect agreement with the Habs fit predicted value of 1.45(25) e 2 b 2 listed in the Appendix.Systematic trends may indicate cases where more measurements are necessary.…”

Measurement of the Excited Energies Identified in 42Ca using the ROSPHERE Gamma-ray Arrays.

“…In the Coulomb unsafe reaction of 192 Os target with the 18 O beam at 80 MeV using the 9 MV tandem accelerator of the Horia Hulubei National Institute of Physics and Nuclear Engineering (known as IFIN-HH) in Bucharest [3], a fusion multiparticle of 2n2p was evaporated from the fusion of 28 Si target with 18 O -beam. 28 Si was found to be one of the impurities in the 192 Os target foil material bought from the Trace company in USA.…”

Isotopically Enriched 192Os Target Preparation using the Electron-gun Beam Method at Target Preparation Laboratory, Daresbury, UK.

“…The procedure followed during the Os through a 2 neutron transfer reaction (Daniel, 2017;Daniel, et al, 2017) is not an exception from the listed challenges above. Owing to the fact that Osmium-192 isotope is one of the heaviest stable isotope (Fremlim and Walters, 1952) of the Osmium nucleus with 116 neutrons as compared to the other 6 stable isotopes (National Nuclear Data Centre) (details of the isotopic composition of Osmium is shown in Table 1), its preparation required special techniques other than just the normal thermal evaporation and other heating methods normally used during the preparation.…”