Conversion coefficients and band assignments in Ta-180

The conversion coefficients for several bandhead decays in Ta-180 have been measured using pulsed-beam techniques and the Yb-176(Li-7,3n)Ta-180 reaction. The spin and parity of the 520 keV Intrinsic state is established as 4(+) and several earlier assignments are confirmed. Two-quasiparticle configurations for the 520 and 592 keV states are discussed and following reanalysis of the band properties, a consistent interpretation is reached. The 520 keV 4(+) state is associated with the favored coupling of the nu 1/2(-)[521]x pi 9/2(-)[514] configuration while the 592 keV (5(+)) state is identified with the nu 1/2(-)[510]x pi 9/2(-)[514] configuration

K-Pi=6+ and 8- isomer decays in HF-172 and DELTA-K=8 E1 transition rates

A recoil-shadow measurement of isomer decay in 172Hf has revealed many weak gamma-ray transitions. One of these is a sevenfold K-forbidden E1 transition from the K(pi) = 8- isomer (T1/2 = 163 ns) to the K(pi) = 0+ ground-state band. The low hindrance factor for this transition in Hf-172 is compared with the hindrance factors for other DELTAK = 8 E1 transitions

Resolution of the w-179-isomer anomaly: exposure of a Fermi-aligned s-band

The K-pi = 35-/2, five-quasiparticle isomer in W-179 is shown to decay into the region of a backbend in the 7-/2[514] band, allowing for the first time the identification of a full set of aligned-band states. Destructive interference results from level mixing in the band-crossing region. The deduced gamma-ray branching ratios are used to establish the mixing matrix elements and to show that the aligned band has a high value of the K quantum number. The properties of well-defined alignment and yet also high K provide the first clear example of a Fermi-aligned s band. The anomalous decay of the isomer itself is now explained

Occurrence of a chiral-like pair band and a six-nucleon noncollective oblate isomer in ¹²⁰I

We report for the first time two distinctive features in the odd–odd nucleus 120 I: a pair of doublet bands and a high-spin isomer built on the πh11/2νh11/2 configuration. For producing the excited states of 120 I, a fusion-evaporation reaction 118 Sn( 6 Li, 4n) at E =lab48 MeV was employed. The beam was provided by the 14UD tandem accelerator of the Heavy Ion Accelerator Facility at the Australian National University. The observed doublet structure built on the positive-parity states is the first case and unique in isotopes with Z=53 . The emerging properties are indicative of the known chiral characteristics, leading to a doubling of states for the πh11/2νh11/2 configuration. In contrast, the high-spin isomer with a half-life of 49(2) ns at spin-parity Jπ=25+ can be explained in terms of a noncollective oblate structure with the full alignment of six valence nucleons outside the 114 Sn core: three protons (g7/2)1(d5/2)1(h11/2)1 and three neutrons (h11/2)3 . This is an outstanding case that reveals a pure single-particle structure consisting of equal numbers of valence protons and neutrons outside the semi-double shell closure of 114 Sn with Z=50 and N=64 .Dr. C. Yuan acknowledges the National Natural Science Foundation of China (11775316

Spherical and deformed isomers in Pb-188

Several isomers in Pb-188 have been identified using pulsed beams, the recoil-shadow technique, and the Er-164(Si-28,4n) Pb-188 reaction. Two of the isomers feed the 10(+) state of the yrast sequence and are suggested to be the 11(-) and 12(+) states from oblate and spherical configurations, respectively. The 12(+) isomer is fed weakly by another isomer with a relatively long lifetime, but it has not been characterized. A fourth isomer with a lifetime of about 1.2 mu s leads via a complicated path to the 8(+) and lower spin yrast states. It is a candidate for the K-pi = 8(-), two-quasineutron state which occurs systematically in N = 106 prolate-deformed nuclei, supporting the assumption that the intruding collective well is prolate

Neutron-particle and proton-hole excitations in the N=128 isotones 208Hg and 209Tl from spectroscopy following 208Pb+238U deep-inelastic reactions

Gamma rays in the π-2ν2 nucleus 208Hg and π-1ν2 nucleus 209Tl have been studied at Gammasphere using deep-inelastic reactions induced by a 1360 MeV208 Pb beam on a thick 238U target. Previously unknown yrast γ-ray cascades above the 8+ and 17/2+ nanosecond isomers in 208Hg and 209Tl, respectively, were identified in coincidence with known γ rays deexciting the isomers. Yrast levels up to spin 13- in 208Hg have been located, and they are interpreted in light of the structure of the 210Pb isotone and with the help of shell model calculations. Shell model calculations by using the Vlow-k realistic interaction have been performed for 210Pb and 208Hg, and compared with experiment. The V low-k effective Hamiltonian seems to account well for the properties of these neutron-rich shell model nuclei

Spherical and deformed structures in Pb189

γ-ray spectroscopy of high-spin states of the neutron-deficient nucleus Pb189 has been conducted with the Gd158(Ar36,5n) and Er164(Si29,4n) reactions. With the first of these, detection of evaporation residues and mass gating were used to unambiguously assign a number of prompt γ-ray transitions to Pb189. With the second reaction and a pulsed beam, an isomer with a mean life of 32 μs was found. Although inconclusive, the available evidence favors identification of the isomer with the 332+ state of the ν(i13/2)-3 configuration. The levels observed below the isomer can be identified with states involving three different structures: the neutron (i13/2)-3 multiplet in the spherical well; a prolate-deformed band involving mixed i13/2 neutron orbitals; and a state with the oblate π(2p-2h)0+ν(i13/ 2)-1 configuration. The evidence for structures associated with different shapes is supported by the observation of E0 components in some of the Jπ→Jπ transitions linking them

Systematics of K-pi=8(-) isomers in N=74 nuclei

An isomer with a half-life of 6+/-1 mu s has been observed in the N=74 nucleus Gd-138, populated following the reaction Cd-106(Cl-35,p2n)Gd-138. Th, isomer decays via a 583 keV EI transition with a hindrance per degree of K forbiddenness, f(v)=24. This value is similar to the values measured for the N=74 isotones Nd-134 and Sm-136 but markedly different from that measured for Ba-130. This suggests that there is some change in structure across the N=74 isotones and possible explanations of this feature are discussed

Connections between high-K and low-K states in the s-process nucleus Lu176

Gamma-ray branches that connect high-K states to low-K states in the s-process nucleus Lu176 were observed, thus providing a link between the 58 Gyr, 7- ground state and the 5.3 h, 1- isomeric state. High sensitivity and unambiguous placement were achieved through the study of the decay of the 58 μs Kπ=14+ isomer using γ-γ-coincidence measurements. The large number of decay paths from the isomer provides a means of populating a broad selection of states from above, resulting, paradoxically, in higher sensitivity than in cases where low-spin input reactions are used. The out-of band decay widths important for excitation processes in stars are quantified

Rotation of an eight-quasiparticle isomer

A T-1/2 = 220 ns, eight-quasiparticle isomer, with four unpaired neutrons and four unpaired protons, has been established at an excitation energy of 6576 keV in the prolate deformed nucleus, W-178. The associated rotational band has also been identified, revealing the collective properties in the presence of blocked pairing correlations, with expected quenching of the nuclear superfluidity. The band retains a small degree of rotational alignment, and has a less-than-rigid dynamic moment of inertia