High-Spin States in Neutron-Rich Tantalum Isotopes

Deep-inelastic reactions between 6.2 MeV/A Xe-136 ions and a thick W-186 target have been used to investigate excited states in neutron-rich tantalum isotopes, establishing new structures in Ta-182 and Ta-183. Spins and parities were determined from angular correlations, internal conversion coefficients deduced from intensity balances, and consideration of transition strengths. The structure and configuration assignments have been established from the measured magnetic properties and alignments of the observed rotational bands, as well as comparison with multi- quasiparticle calculations. Multi-quasi particle calculations using adjusted Nilsson energies and Lipkin-Nogami pairing model were performed for the series of tantalum nuclei between A=181 and A=185.The previously known 1300 ns isomer in Ta-183 was fully characterised with its energy deduced as 1332 keV and a K = 19/2+ assignment. Several new multi-quasiparticle states, including two isomers with 41(5) ns mean-life, K = 29/2- and 70(4) ns (mean-life), K = 41/2-, have been further identified and found to be feeding the known 1300 ns isomer. From the multi-quasiparticle calculations, a three-quasiparticle configuration was assigned to both the K = 19/2+ and 29/2- isomers, while the upper-most isomer at 41/2- was established to have a five-quasiparticle nature.The out-of-beam gamma-ray coincidence data revealed a new level structure in coincidence with tantalum X-rays. Measurements of the magnetic properties of this structure from branching ratios, together with the yields from various data sets using W-186, Re-185, Re-187 and Os-192 targets, enabled an isotopic assignment of this structure to Ta-182. Three isomeric states were found to be feeding the known 10-> isomer in Ta-182. A rotational band built on the 10- isomer has been > observed and was found to be fed by a new 14+, 356 ns (mean-life) > isomer at 1950 keV. Several intrinsic states above this isomer are > also identified. Firm spins and parities have been established up to > the 14+ isomeric state. Due to limited spectroscopic information, the > spins and parities for the levels above this isomer are tentative.The structure of Ta-182 and Ta-183 are also investigated by comparing the measured transition strengths with similar transitions in the mass region. Most of the transition strengths measured are in good agreement with expectations in the region, except for a few cases of E1 decays that are anomalous. Possible explanations for some of these anomalous transition strengths have been discussed.Few cases has been observed where the predicted yrast states are not observed experimental in both Ta-182 and Ta-183. Possible explanations have been discussed as well.Both the calculations and experimental results suggest a high density of intrinsic states occurs along the yrast line at high excitation energy in both nuclei. This pattern seems to emerge in the more neutron-rich tantalums isotopes resulting in a more complex level scheme that is difficult to interpret

Levels in 210Fr and the decay of a high-spin, multi-particle isomer

The structure of 210Fr has been studied through the 197Au(18O, 5n)210Fr reaction. A high-spin iso-meric state has been identified at ∼4.4 MeV. It has a lifetime of 686(17) ns and decays by two γ-rays that are very likely to be either M2 or E3 multipol

Three-quasiparticle isomers and possible deformation in the transitional nuclide, 195 Au

Deep-inelastic reactions and γ-ray spectroscopy have been used to study excited states in 195Au. A three-quasiparticle isomer with a mean-life of 18.6(3) μs has been assigned at 2461+Δ keV, with decays into newly identified structures. Possible config

Decay of a three-quasiparticle isomer in the neutron-rich nucleus 183Ta

Excited states in neutron-rich tantalum isotopes have been studied with deep-inelastic reactions using 136Xe ions incident on a 186W target. New transitions observed below the τ=1.3 μs isomer in 183Ta have enabled the establishment of its energy and pu

Isomers and alignments in 191Ir and 192Os

Deep-Inelastic reactions have been used to populate high-spin states in the even-even osmium isotopes and in the iridium neighbors. New isomers have been identified in 190Os, 192Os, 194Os, 191Ir and 193Ir. These include a 2 ns 12 + state at 2865 keV and a 295 ns, 20 + state at 4580 keV in 192Os. Although a number of multi-quasiparticle states arising from prolate and triaxial deformations are expected in these nuclei, the main structures in 192Os can be interpreted as a two-stage alignment of i 13/2 neutrons at oblate deformation, in close analogy with similar structures in the isotones 194Pt and 196Hg. The isomers are attributed to low-energy E2 transitions at the point of the alignment gains. The isomer observed in 191Ir is long-lived (τ m ∼8s) and probably arises from coupling of the h 11/2 proton to the 10 -ν/9/2 - [505]11/2 + [615] prolate configuration that gives rise to long-lived isomers in 190Os and 192Os, although potential-energy-surface calculations indicate that the resultant three-quasiparticle state will be triaxial

Long-lived three-quasiparticle isomers in 191Ir and 193Ir with triaxial deformation

Deep-inelastic reactions have been used to populate high-spin states in the iridium isotopes. New results include the identification of particularly long-lived three-quasiparticle isomers in 191Ir and 193Ir, with mean-lives of 8.2(7) s and 180(3) μs res

Improved precision on the experimental E0 decay branching ratio of the Hoyle state

Background: Stellar carbon synthesis occurs exclusively via the 3α process, in which three α particles fuse to form 12C in the excited Hoyle state, followed by electromagnetic decay to the ground state. The Hoyle state is above the α threshold, and the rate of stellar carbon production depends on the radiative width of this state. The radiative width cannot be measured directly, and must instead be deduced by combining three separately measured quantities. One of these quantities is the E0 decay branching ratio of the Hoyle state, and the current 10% uncertainty on the radiative width stems mainly from the uncertainty on this ratio. The rate of the 3α process is an important input parameter in astrophysical calculations on stellar evolution, and a high precision is imperative to constrain the possible outcomes of astrophysical models.The project was supported by the Australian Research Council Discovery Grants No. DP140102986, No. DP170101673, and No. DP170102423. Operation of the ANU Heavy Ion Accelerator Facility is supported by the NCRIS HIA capability. The support from technical staff for the development of the pair spectrometer, as well as during the long experimental runs, is greatly appreciated. This work was partially supported by the International Joint Research Promotion Program of Osaka University and JSPS KAKENHI Grant No. JP 17H02893, the Natural Sciences and Engineering Research Council of Canada, the National Research Foundation (NRF), South Africa, under Grants No. 93533 and No. 118645

Spectroscopy and high-spin structure of Fr-210: Isomerism and potential evidence for configuration mixing

The structure of 210Fr has been established up to an excitation energy of ∼5.5 MeV and spins of ∼25, via time-correlated γ -ray spectroscopy and using the 197Au(18O,5n) 210Fr reaction with pulsed beams at an energy of 97 MeV. A significantly different level scheme has been obtained compared to previous publications. Several isomers are reported here, including a J π = (23)+, τ = 686(9)-ns state at 4417 keV and a 10−, 29.8(11)-ns state at 1113 keV. The former isomer has been associated with the π(h3 9/2i2 13/2)ν(p−2 1/2f −1 5/2 ) configuration and decays via proposed E3 transitions with strengths of 8.4(3) and 21.2(8) W.u. There are only very few known cases of a high-spin isomer decaying via two parallel E3 transitions. Indeed, this is not seen in other Fr nuclei, and consequently these strengths differ from related decays in the neighboring isotopes. However, by examining the systematics of E3 transitions in trans-lead nuclei, we suggest that the weaker of the two transitions decays to a mixed 20− state. Systematics of the 10− isomer are also discussed. Comparisons are made between the observed spectrum of states and those predicted from semiempirical shell-model calculations

High-spin spectroscopy and shell-model interpretation of the N < 126 radium isotopes 212Ra and 213Ra

The level structures of Ra212 and Ra213 have been established via time-correlated γ-ray spectroscopy following the Pb204(C12,4n)Ra212 and Pb204(C13,4n)Ra213 reactions. In Ra212, levels up to ∼6.2MeV were identified and firm spin-parity assignments were achieved to a Jπ=19+ isomer with a mean life of 31(3) ns. For Ra213 the corresponding values were ∼4.5MeV in excitation energy and Jπ=33/2+. Two isomeric states with Jπ=23/2+, τ=27(3) ns and Jπ=33/2+, τ=50(3) ns were discovered in Ra213. The experimental data were compared with semiempirical shell-model calculations, which allowed dominant configurations to be assigned to most of the observed levels.This research was supported in part by the Australian Research Council, Grants No. DP120101417, No.DP130104176, No. DP140102986, No. DP140103317, and No. FT100100991. A.A. and M.S.M.G. acknowledge support of the Australian Government Research Training Program