Long-lived isomers in 190Ir

Physical Review Letters, 2013

Long-lived isomers in 212 Bi have been studied following 238 U projectile fragmentation at 670 MeV per nucleon. The fragmentation products were injected as highly charged ions into the GSI storage ring, giving access to masses and half-lives. While the excitation energy of the first isomer of 212 Bi was confirmed, the second isomer was observed at 1478(30) keV, in contrast to the previously accepted value of >1910 keV. It was also found to have an extended Lorentz-corrected in-ring halflife >30 min, compared to 7.0(3) min for the neutral atom. Both the energy and half-life differences can be understood as being due a substantial, though previously unrecognised, internal decay branch for neutral atoms. Earlier shell-model calculations are now found to give good agreement with the isomer excitation energy. Furthermore, these and new calculations predict the existence of states at slightly higher energy that could facilitate isomer de-excitation studies.

Physical Review C, 2014

Using fusion-evaporation reactions, a gas-filled recoil separator, and recoil-electron and recoil-electron-α tagging techniques, a new isomeric 1 2 + state [T 1/2 = 45(3) ms] in 201 At is identified, and an earlier reported corresponding state [T 1/2 = 273(9) ms] in 199 At is confirmed. The 1 2 + state is suggested to originate from an intruder π (s 1/2) −1 configuration. In addition, nuclear structure of states below and above this 1 2 + state are studied in both nuclei. The isomer decays through a cascade of an E3 transition followed by a mixed M1/E2 transition to the 9 2 − ground state, and it is interpreted to be fed from nearly spherical 3 2 + and 5 2 + states originating from π (d 3/2) −1 and π (d 5/2) −1 configurations, respectively.

Physical Review Letters, 2001

Excited states in 216 Th were investigated via prompt and delayed g decays and the recoil-decay tagging method. The decay schemes of the I p ͑8 1 ͒, t 1͞2 128͑8͒ ms, the I p ͑11 2 ͒, t 1͞2 615͑55͒ ns, and the I p ͑14 1 ͒, t 1͞2 $ 130 ns isomers were established. The configuration ph 9͞2 f 7͞2 is assigned to the I p ͑8 1 ͒ isomer, which implies that the h 9͞2 and f 7͞2 states are nearly degenerate. This is ascribed to increased binding of the f 7͞2 orbital by its coupling to a low-lying I p ͑3 2 ͒ state at E x 1687 keV. The role of octupole and pairing correlations for a Z 92 shell closure prediction is discussed on the basis of shell model calculations.

The European Physical Journal A - Hadrons and Nuclei, 2000

Lifetime measurements of states in nuclei with A=187 and 188 have been performed, using reactions between 155 Gd and 36 Ar and following the transport of evaporation residues to the focal plane of a gas-filled recoil separator. In a separate experiment using the 159 Tb( 32 S,4n) reaction the γ-decay of isomeric levels in 187 Tl has been studied using delayed γ-γ coincidence measurements. From observation of their subsequent γ decay, the mean lifetimes were measured to be 1000 ± 55 ns and 1600 ± 100 ns. Although it was not possible to characterize the isomers completely, they are proposed as candidates for one-proton, two-neutron excitations. In the course of this study, the decay of an isomer in 188 Pb was also observed and its lifetime was measured as 1150 ± 30 ns, and limits of 20-600 ns were placed on the meanlife of an isomer conjectured in 187 Pb.

The European Physical Journal A, 2002

Prompt and delayed gamma-ray spectroscopy of very neutron-deficient bismuth isotopes 187,189 Bi has been performed using the Recoil Decay Tagging (RTD) method. The isomeric i 13/2 states have been identified and their lifetimes have been measured. The systematics of these long-lived M 2 isomers has been extended to the proton-unbound isotopes. The general behaviour of single-proton states is discussed within the systematics and interpreted within the shell-model framework.

The European Physical Journal A, 2008

The lifetime of the recently discovered six-quasiparticle (6-qp) isomer in 140 Nd has been measured using the 126 Te(18 O, 4n) reaction and the pulsed-beam technique at the Institut de Physique Nucléaire (IPN) Orsay. The deduced lifetime of the 6-qp isomer in 140 Nd of 1.23(7) µs supports the 20 + spin-parity assignment to the isomeric state which is based on a spherical configuration that coexists with the triaxial bands observed in this spin range. Evidence for delayed components for the transitions below the 19/2 + state in 139 Nd was observed, with an apparent half-life of 272(4) ns.

Physical Review C, 2008

The medium-spin structure of the neutron-rich, odd-odd nucleus 94 Rb was studied by means of γ-ray spectroscopy. Excited levels were populated in the neutron-induced fission of 235 U and in the spontaneous fission of 252 Cf and 248 Cm. Two isomeric states were found at 1485.2 and 2074.8 keV with half-lives of 18 and 107 ns, respectively. The probable structures of the two isomers involve the fully aligned, proton-neutron configurations [π (g 9/2) ⊗ ν(g 7/2)] 8 + and [π (g 9/2) ⊗ ν(h 11/2)] 10 − , respectively. These new data give information on the single-particle energies in the region.

Nuclear Physics A, 2003

The level scheme of 181 76 Os has been investigated with the 150 Nd(36 S,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 181 Os. In the higher-spin regime, two new high-K intrinsic states, with K π = 37/2 + and K π = 41/2 + , were established, along with the fragmented decay of a K π = 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 K π = 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 K π = 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 K π = 41/2 + configuration is less susceptible to distortions in the γ plane than any of the other high-K states.

The European Physical Journal A - Hadrons and Nuclei, 2004

A new high-spin isomer in 150 Dy has been observed at an excitation energy of 10.3 MeV by combining the inverse-kinematic reaction induced by a pulsed beam of 132 Xe and the γ-ray recoil-shadow technique. The half-life of this isomeric state has been determined to be T 1/2 = 1.6 ± 0.6 ns using the conventional centroid-shift method with the 141 Pr( 16 O, p6n) 150 Dy reaction at 165 MeV. The mechanism producing high-spin isomers in N = 83, 84 isotones is qualitatively discussed in terms of the difference of the neutron particle-hole configuration between the high-spin isomer and the lower-lying state.

Physical Review C

A six-quasiparticle isomer with T 1/2 = 57(2) ns has been established in the doubly-odd isotope 200 Tl and its level scheme is significantly extended. Half-lives of previously reported isomers in 200 Tl and 201,202 Pb have been determined and revised values are reported in a few cases, with T 1/2 = 397(17) ns and 7.0(5) ns for the I π = 5 + and 7 − states in 200 Tl, 52(2) ns for the 41/2 + level in 201 Pb, and 93(4) ns for the 16 + state in 202 Pb. Configurations for the isomers have been assigned and these predominantly involve intrinsic excitations of neutrons from the i 13/2 subshell. The inferred transition rates for the decay of these isomers compare well with single-particle estimates attesting to their intrinsic character.