Quasiparticle alignments and alpha-decay fine structure of Pt-175

Excited states and decay properties of 175 Pt have been investigated using the 92 Mo ( 86 Sr , 2 p n ) fusion-evaporation reaction. The JUROGAM I γ -ray spectrometer and the GREAT spectrometer were used in conjunction with the gas-filled recoil separator RITU for the measurement of the radiation at the target and focal plane positions, respectively. Two new band structures, assigned to be based on the I π = ( 7 / 2 − ) ground state in 175 Pt, have been established and the known yrast band has been extended up to I π = ( 49 / 2 + ) . Rotational properties of the excited states in 175 Pt have been investigated within the cranked shell-model formalism. The low-frequency changes in the alignments of the positive- and negative-parity bands are interpreted as a sign of proton-pair excitations in the rotating core. Furthermore, the α -decay measurements reveal a candidate for a fourth α -decay branch in 175 Pt, feeding a non-yrast state in 171 Os

Decay of (201-203)Ra and 200-202Fr

Decay properties of the neutron-deficient nuclides 201-203Ra and 200-202Fr were investigated using α- and γ-decay spectroscopy. The nuclei were produced in fusion-evaporation reactions of 56Fe projectiles with enriched 147Sm and 149Sm targets at the velocity filter SHIP at GSI in Darmstadt (Germany). The α decay from the (3/2-) state in 201Ra was identified with an energy Eα=7842(12) keV and half-life T1/2=8-4+40 ms. Ambiguous decay properties for 202Ra from previous measurements were clarified by remeasuring with significantly improved precision, resulting in values of Eα=7722(7) keV and T1/2=3.8-0.8+1.3 ms. New short-lived isomeric states were identified in 200Fr and 201Fr with half-lives of 0.6-0.2+0.5 μs and 0.7-0.2+0.5 μs, respectively. A tentative spin and parity of 13/2+ were assigned to the latter. One event attributed to β-delayed fission of 200Fr was observed. © 2014 American Physical Society.status: publishe

Decay of the 9/2- isomer in 181Tl and mass determination of low-lying states in 181Tl, 177Au and 173Ir

A detailed spectroscopic study of the neutron-deficient isotope 181Tl and the daughter of its α decay, 177Au, has been performed in the complete fusion reaction 40Ca + 144Sm → 184Pb∗ at the velocity filter SHIP (GSI). The mass excess, excitation energy, and decay scheme of the isomeric 1.40(3) ms, 9/2− intruder state in 181Tl have been established for the first time. These results solve a long-standing puzzle of the unrealistically large reduced α-decay width of this isomer. Based on this, the previously unknown masses of the long-lived isomeric states in 177Au and 173Ir have been derived. In turn, it now allows the excitation energies of previously identified bands in 177Au and 173Ir to be deduced and compared with theoretical predictions. First measurements of α-decay branching ratios for 181Tlm and 177Aum,g are also reported.status: publishe

Alpha decay of 180,181Pb

A detailed alpha-decay study of the neutron-deficient isotope 181Pb has been performed in the complete fusion reaction 40Ca+144Sm->184Pb* at the velocity filter SHIP (GSI, Darmstadt). In comparison with the literature, more precise data have been deduced for the I = (9/2−) ground state in this nucleus, which is presumably based on the neutron h9/2 spherical orbital. Improved alpha-decay data were also measured for 180Pb.status: publishe

First observation of excited states in 175Hg

Excited states of the neutron-deficient nucleus Hg175, populated using fusion-evaporation reactions, are reported for the first time. The spin and parity of the ground state has been determined to be Iπ=7/2− through measurements of the α decay to the daughter nucleus Pt171. A structure based on an isomeric state [T1/2=0.34(3) μs] with Iπ=13/2+ and its decay path to the ground state have been established. The observed structures are interpreted in terms of single-particle configurations, and the trends of coexisting shapes in neighboring nuclei are discussed

The new isotope 179Pb and alpha-decay properties of 179Tlm

The new isotope 179Pb has been produced in the complete fusion reaction 40Ca+144Sm->179Pb+5n at the velocity filter SHIP (GSI). Its alpha-decay energy of 7350(20) keV and half-life value 3.5 (+1.4/-0.8) ms were deduced based on the recoil-alpha-alpha correlation technique. A spin parity of I=(9/2-) was tentatively assigned to the ground state of 179Pb; thus, it is based on the 1h9/2 orbital. Improved measurements of the alpha-decay properties of 179Tlm and 175Aum are also presented.status: publishe

Identification and decay of the 0.48ms 13/2+ isomer in 181Hg

A new isomer with a half-life of 0.48(2) ms was identified in the nuclide 181Hg, which was produced in the complete fusion reaction 40Ca + 144Sm → 184Pb* at the velocity filter SHIP (GSI, Darmstadt). The isomeric state was tentatively assigned a spin-parity of 13/2+. We propose that this isomer de-excites by a yet unobserved low-energy, strongly converted gamma-ray transition, followed by a newly identified cascade composed of a 90.3 keV M1 and a 71.4 keV E2 gamma-ray transition.status: publishe

Gamma-ray spectroscopy approaching the limits of existence of atomic nuclei : a study of the excited states of 168Pt and 169Pt

Excited states in the N=90 and N=91 Pt nuclei have been investigated using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. These nuclei were populated via the reactions Mo92(Kr78,2n) and Mo94(Kr78,3n) at 335 and 348 MeV, respectively. The recoil-decay tagging technique has been used to correlate prompt γ radiation with the characteristic α decays of Pt168 and Pt169. A γ-γ analysis has allowed a level scheme for Pt168 to be reported for the first time and the level scheme for Pt169 to be extended. The excitation energies of the proposed positive-parity yrast states of Pt168 are compared with calculations based on the interacting boson model and found to be in excellent agreement. These data show a continuation of the trend toward vibrational nuclei as the N=82 shell gap is approached. In addition, new excited states constituting two decay paths have been discovered in Pt169

Competing quasiparticle configurations in W-163

Excited states in the neutron-deficient nuclide W163 were investigated using the Cd106(Ni60,2pn)W163 reaction at a beam energy of 270 MeV. The level scheme for W163 was extended significantly with the observation of five new band structures. The yrast band based on a 13/2+ isomeric state is extended up to (57/2+). Two band structures were established on the 7/2− ground state. Quasiparticle configuration assignments for the new band structures were made on the basis of cranked Woods-Saxon shell-model calculations. The results reported in this article suggest that the negative-parity ν(f7/2,h9/2) orbitals are responsible for the first rotational alignment in the yrast band