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Deep inelastic and transfer reactions with an 820-MeV, 136Xe beam and various ytterbium and lutetium targets have been employed to study high-spin structures in the neutron-rich thulium isotopes beyond 171Tm. Results in the doubly odd nucleus, 174Tm, include the identification of numerous new two- and four-quasiparticle intrinsic states including several isomers below 1 MeV, and the observation of the Kp=4- ground state rotational band populated via direct decay from a t=153(10)-µs, Kp=14- isomer at 2092 keV. The 398-keV, M1 transition linking the isomer and ground state band is abnormally fast for a highly forbidden, ?K=10 decay. This relative enhancement is explained in terms of mixing of the 13- level with the nearby 13- member of a Kp=8- rotational band, with an interaction strength of V 1.4 keV. Multiquasiparticle calculations are compared with the observed states. [ABSTRACT FROM AUTHOR]

High-spin states in the odd-proton thulium isotopes 173Tm and 175Tm have been studied using deep-inelastic reactions and γ-ray spectroscopy. In l73Tm, the low-lying structure has been confirmed and numerous new states have been identified, including a three-quasiparticle Kπ = 19/2- isomer with a lifetime of τ = 360(100) ns at 1906 keV and a five-quasiparticle Kπ = 35/2- isomer with a lifetime of τ = 175(40) ns at 4048 keV. The Kπ = 35/2- state is interpreted as a t-band configuration that shows anomalously fast decays. In 175Tm, the low-lying structure has been reevaluated, a candidate state for the 9/2- [514] orbital has been identified at 1175 keV, and the 7/2-[523] bandhead has been measured to have a lifetime of τ = 460(50) ns. Newly identified high- AT structures in 175Tm include a Kπ = 15/2- isomer with a lifetime of τ = 64(3) ns at 947 keV and a Kπ = 23/2- isomer with a lifetime of τ = 30(20) µs at 1518 keV. The Kπ = 15/2- isomer shows relatively enhanced decays to the 7/2-[523] band that can be explained by chance mixing with the 15/2- member of the 7/2- band. Multiquasiparticle calculations have been performed for 173Tm and l75Tm, the results of which compare well with the experimentally observed high-spin states. [ABSTRACT FROM AUTHOR]

The level structure of the odd-odd iodine nucleus 122I has been studied by the 120Sn(7Li, 5n) 122I reaction at Elab = 58 MeV. Two chopped beams from the 14UD (Unit Doubled) tandem heavy-ion accelerator at the Australian National University were used; one was a nanosecond (ns) pulsed-beam with separation of 1.7 microseconds (μs) and the second one was a 60-μs beam separated by 880 μs. Through in-beam and out-of-beam γ-ray spectroscopy, the complex proton-neutron multiplet states, including isomers with half-lives of a few tens of ns to a few tens of μs, have been identified. Collective states based on the proton h11/2 orbital exhibit two kinds of structure depending upon the coupled neutron orbital: a quadrupole vibration when involving the h11/2 orbital and a γ-soft deformed rotation when involving the g7/2 orbital. With spherical shell model and deformed shell-model calculations, the observed level structures are explained. [ABSTRACT FROM AUTHOR]

The structure of 210Fr has been established up to an excitation energy of ∼5.5 MeV and spins of ∼25ℏ, via time-correlated γ-ray spectroscopy and using the Au197(O18,5n)Fr210 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 Jπ=(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 (h9/2³i13/2²)ν(p1/2-2f5/2-1) 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. [ABSTRACT FROM AUTHOR]

An excited metastable nuclear state of 192Os in a hydrogen-like charge state has been studied for the first time. It was populated in projectile fragmentation of a 197Au beam on a 9Be target with the UNILAC-SIS accelerators at GSI. Fragmentation products in the region of interest were passed through the fragment separator and injected into the experimental storage ring (ESR). Cooling of the injected beam particles enabled Schottky mass spectrometry to be performed. Analysis shows the lifetime of the state to be considerably longer than that of the neutral ion [τneut = 8.5(14) s]; this change is attributed to hindrance of internal conversion in hydrogen-like 1920s. Calculations have been performed to estimate the lifetime, and the result has been compared with that measured experimentally. There is good agreement between the expected [τH-like = 13.0(24) s] and measured lifetimes (τrest = 15.1-1.3+1.5 s) from the internal decay of 192mOs. This provides a test for the reliability of the values obtained from internal conversion coefficient calculations in highly ionized systems and is the first measurement of its kind to be performed using the ESR setup. [ABSTRACT FROM AUTHOR]

The yrast structure of 207Pb above the 13/2+ isomeric state has been investigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Argonne National Laboratory. New and previously observed transitions were measured using the Gammasphere detector array. The level scheme of 207Pb is presented up to ~ 6 MeV, built using coincidence and γ-ray intensity analyses. Spin and parity assignments of states were made, based on angular distributions and comparisons to shell model calculations. [ABSTRACT FROM AUTHOR]

A study of neutron-rich isotopes in the A = 185 region of the nuclear chart has uncovered long-lived (>1 s) isomers in several isotopes of hafnium, tantalum, tungsten, rhenium, and osmium. The region was accessed via the use of projectile fragmentation with the UNILAC-SIS accelerators at GSI. Fragmentation products of 197Au were passed through the fragment separator (FRS) and injected into the experimental storage ring (ESR), where single-ion identifications could be made. Evidence is presented for isomers in 183,184,186Hf 186,187Ta 186W, 190,192,194Re, and 195Os with excitation energies in the range of 0.1-3.0 MeV. The lightest of these nuclides have well deformed prolate shapes, while the heaviest are transitional and susceptible to shape changes. Their properties are interpreted with the help of multi-quasiparticle and potential-energy-surface calculations. [ABSTRACT FROM AUTHOR]

The half-life of a Kπ = 12+ isomer in 164Er has been measured to be 68(2) ns, and new decay pathways have been identified. These include highly K-forbidden y-ray transitions directly to the ground-state rotational band, with reduced hindrance values that can be compared with those found for heavier nuclides. The new data support the interpretation that the level density is a key variable in determining K-forbidden transition rates. [ABSTRACT FROM AUTHOR]

Configuration-constrained potential-energy-surface calculations have been performed to investigate multiquasiparticle high-if states built on superdeformed minima in 192,194,196Pb and 198Po. The calculations predict that 196Pb and 198Po would be favorable candidates for the observation of low-lying superdeformed two- and four-quasiparticle high-K states. The possible decay paths and lifetimes that could lead to isomers are evaluated in detail for 196Pb. Comparisons between the predictions and previous observations of octupole-vibrational excitations indicate also that bands built on superdeformed high-K intrinsic states may compete with the octupole-vibrational mode in this mass region. The quadrupole moments of both the collective and intrinsic excitations are analyzed. [ABSTRACT FROM AUTHOR]

ß decays from heavy, neutron-rich nuclei with A ∼ 190 have been investigated following their production via the relativistic projectile fragmentation of an E/A = 1 GeV 208Pb primary beam on a ∼2.5 g/cm2 9Be target. The reaction products were separated and identified using the GSI FRagment Separator (FRS) and stopped in the RISING active stopper, γ decays were observed and correlated with these secondary ions on an event-by-event basis such that y-ray transitions following from both internal (isomeric) and β decays were recorded. A number - of discrete, β-delayed γ-ray transitions associated with β decays from 194Re to excited states in 194Os have been observed, including previously reported decays from the yrast Iπ = (6+) state. Three previously unreported y-ray transitions with energies 194, 349, and 554 keV are also identified; these transitions are associated with decays from higher spin states in 194Os. The results of these investigations are compared with theoretical predictions from Nilsson multi-quasiparticle (MQP) calculations. Based on lifetime measurements and the observed feeding pattern to states in 1940s, it is concluded that there are three β--decaying states in 194Re. [ABSTRACT FROM AUTHOR]

The anomalously fast decay of a 19/2+ three-quasiparticle isomer in l7lTm was interpreted recently as an example of K mixing induced by a very small mixing matrix element but a (random) close proximity to a collective state. To understand the source of the residual interaction we have generalized the projected shell model by introducing two-body octupole and hexadecupole forces into the Hamiltonian and expanding the model space with inclusion of specific three-quasiparticle configurations. It is found that the K mixing is built up from small interactions transferred through numerous highly excited configurations that contain high-7 orbitals. While the chance near-degeneracy enhances the transition strength, the octupole correlation and Coriolis coupling produce the mixing matrix element. [ABSTRACT FROM AUTHOR]

High-spin states in the 16468Er96 region were studied using 9Be + l60Gd reactions. Pulsed beam conditions were exploited for enhanced sensitivity to delayed &ggr;-ray transitions. New isomers were identified in 16lDy, l63Ho, 162Er, and l65Er. The l62Er isomer is interpreted to decay by E1 transitions to the ground-state band with a reduced hindrance of fv = 33. A plot of fv values for all &Dgr;K = 7, E1 transitions from two-quasiparticle isomers to the ground-state bands of even-even nuclei reveals only a small influence from the dynamic to kinematic moment-of-inertia ratio, which provides a measure of Coriolis K mixing within the ground-state band. This is interpreted to imply that the relatively low hindrances are due to K mixing in the isomer, caused by a combination of Coriolis and octupole band mixing. [ABSTRACT FROM AUTHOR]

The 160Gd(9Be,α3n)162Dy reaction has been used to study high-spin states in 162Dy. Pulsed beam conditions were utilized for enhanced isomer sensitivity. An isomer at 2188.1(3) keV with a half-life of 8.3(3) μs has been discovered and assigned Kπ= 8+ with a two-quasineutron configuration. Among 11 γ-ray decay branches, an E2, ΔK=8 transition to the ground-state band was observed with a reduced hindrance of ƒv=35, agreeing well with systematics correlating ƒv with the product of the valence neutron and proton numbers (NpNn) over an extended N,Z range. Small deviations from NpNn dependence are analyzed for a range of two-quasiparticle isomer decays and interpreted as arising from a weak dependence on the isomer excitation energy relative to the yrast line. [ABSTRACT FROM AUTHOR]

The level scheme of 18176Os has been investigated with the 150Nd(36S,5n) reaction. The low-K rotational bands built upon the 9/2+[624], 7/2−[514] and 1/2−[521] neutron configurations have been extended and other new bands established. The configurations of these low-K bands are discussed within the framework of the cranked-shell model. The lifetimes for some of the states in the 9/2+[624] and 1/2−[521] collective rotational bands were also measured using the Doppler Shift Attenuation method. The large deformations deduced are found to be consistent with those predicted from theoretical Total Routhian Surface calculations. These results support the idea that for these low-K states the nuclear shape is axially symmetric and allows the K quantum number to be defined and the associated K-selection rule to be upheld. This behaviour apparently contrasts with that of the higher-K states in 181Os. In the higher-spin regime, two new high-K intrinsic states, with Kπ=37/2+ and Kπ=41/2+, were established, along with the fragmented decay of a Kπ=33/2− intrinsic state. The configurations and excitation energies of these experimentally determined intrinsic states are found to be in excellent agreement with theoretical calculations based on a fixed shape Nilsson model plus BCS pairing. The structures on top of these intrinsic states do, however, show very different behaviour. A relatively regular high-K rotational band was observed on top of the Kπ=41/2+ state but not for the other newly-established intrinsic states. Theoretical configuration-constrained potential energy surface calculations suggest that the irregular transition sequence above the Kπ=37/2+ intrinsic bandhead state, the limited excitations observed above the other intrinsic states and the observation of fragmented and non-hindered decays, are due to these configurations being subject to an appreciable γ softness. These calculations reveal that the Kπ=41/2+ configuration is less susceptible to distortions in the γ plane than any of the other high-K states. [Copyright &y& Elsevier]

The 8He+208Pb reaction was studied in the first experiment with the EXOGAM germanium detector array using beam delivered by the SPIRAL facility. γ-rays from direct and fusion–evaporation reactions were observed with high resolution. γ–γ coincidence data were obtained at a beam intensity level of 105 8He particles per second. Specially designed absorbers and beam detectors could further reduce the background radiation by orders of magnitude. [Copyright &y& Elsevier]

Mass-separated 187Ta114 in a high-spin isomeric state has been produced for the first time by multinucleon transfer reactions, employing an argon gas-stopping cell and laser ionization. Internal γ rays revealed a T1/2 = 7.3 ± 0.9     s isomer at 1778 ± 1 keV, which decays through a rotational band with perturbations associated with the approach to a prolate-oblate shape transition. Model calculations show less influence from triaxiality compared to heavier elements in the same mass region. The isomer-decay reduced E2 hindrance factor fν = 27 ± 1 supports the interpretation that axial symmetry is approximately conserved. [ABSTRACT FROM AUTHOR]

Using the 168Er (10B, 5n) reaction at a beam energy of 68 MeV, new data have been obtained for the population and decay of a T1/2 = 148 ns, Kπ = 21/2- three-quasiparticle isomer at 1717 keV in 173 Ta. Revised decay energies and intensities have been determined, together with newly observed members of a rotational band associated with the isomer. By comparison with other isomers in the A ≈ 180 deformed region, the 173 Ta isomer properties help to specify the key degrees of freedom that determine K -forbidden transition rates. In particular, when all three quasiparticles are of the same nucleon type, there is a strong dependence of the E2 reduced hindrance factor on the isomer excitation energy. [ABSTRACT FROM AUTHOR]

A correction to the article "Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in 254Rf," by H. M. David and colleagues in the September 24, 2015 issue is presented.

Mass-separated ^{187}Ta_{114} in a high-spin isomeric state has been produced for the first time by multinucleon transfer reactions, employing an argon gas-stopping cell and laser ionization. Internal γ rays revealed a T_{1/2}=7.3±0.9  s isomer at 1778±1  keV, which decays through a rotational band with perturbations associated with the approach to a prolate-oblate shape transition. Model calculations show less influence from triaxiality compared to heavier elements in the same mass region. The isomer-decay reduced E2 hindrance factor f_{ν}=27±1 supports the interpretation that axial symmetry is approximately conserved.

The structure of nuclear isomeric states is reviewed in the context of their role in contemporary nuclear physics research. Emphasis is given to high-spin isomers in heavy nuclei, with [Formula: see text]. The possibility to exploit isomers to study some of the most exotic nuclei is a recurring theme. In spherical nuclei, the role of octupole collectivity is discussed in detail, while in deformed nuclei the limitations of the K quantum number are addressed. Isomer targets and isomer beams are considered, along with applications related to energy storage, astrophysics, medicine, and experimental advances.