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Background: The available data for E2 transition strengths in the region between neutron-deficient hafnium and platinum isotopes are far from complete. More and precise data are needed to enhance the picture of structure evolution in this region and to test state-of-the-art nuclear models. In a simple model, the maximum collectivity is expected at the middle of the major shell. However, for actual nuclei, particularly in heavy-mass regions, which should be highly complex, this picture may no longer be the case, and one should use a more realistic nuclear-structure model. We address this point by studying the spectroscopy of Hf as a representative case. Purpose: We remeasure the 21+ half-lives of 172,174,176Hf for which there is some disagreement in the literature. The main goal is to measure, for the first time, the half-lives of higher-lying states of the rotational band. The new results are compared to a theoretical calculation for absolute transition strengths. Method: The half-lives were measured using γ-γ and conversion-electron-γ delayed coincidences with the fast timing method. For the determination of half-lives in the picosecond region, the generalized centroid difference method was applied. For the theoretical calculation of the spectroscopic properties, the interacting boson model is employed, whose Hamiltonian is determined based on microscopic energy-density functional calculations. Results: The measured 21+ half-lives disagree with results from earlier γ-γ fast timing measurements, but are in agreement with data from Coulomb excitation experiments and other methods. Half-lives of the 41+ and 61+ states were measured, as well as a lower limit for the 81+ states. Conclusions: This work shows the importance of a mass-dependent effective boson charge in the interacting boson model for the description of E2 transition rates in chains of nuclei. It encourages further studies of the microscopic origin of this mass dependence. New experimental values on transition rates in nuclei from neighboring isotopic chains could support these studies. [ABSTRACT FROM AUTHOR]

Excited states in the neutron-deficient nucleus 72161Hf89 have been populated using the 118Sn(48Ti,5n) 161Hf and 110Pd(56Fe,5n) 161Hf fusion-evaporation reactions at 240 and 270 MeV, respectively. The level scheme for 161Hf has been extended with the observation of new band structures and an Iπ = (13/2+) isomeric state with a half-life of 4.8(2) μs has been identified. The decay path from this isomer to the (7/2-) ground state is established. The yrast band, based on the (13/2+) isomeric state, is extended up to (73/2+) and side band structures are identified up to (69/2-) and (55/2-). Quasiparticle assignments for these rotational structures are made on the basis of their alignment properties and Woods-Saxon cranked shell-model calculations. [ABSTRACT FROM AUTHOR]

Two new rotational bands of distinct character have been identified in 164Hf. They are suggested to correspond to the long-anticipated triaxial strongly deformed (TSD) bands predicted by theoretical studies. The bands have been linked to known states, and the level spins and energies could be determined. The bands are also substantially stronger in intensity and are located at lower spins than the previously observed TSD bands in l68Hf, hereby making l64Hf the best even-even system so far for the study of TSD structures in the A ~ 160 mass region. Cranking calculations based on the modified-oscillator model suggest that the bands are associated with four-quasiparticle configurations that involve high / intruder (i.13/2)2i proton orbitals. [ABSTRACT FROM AUTHOR]

Whether or not the 178Hfm2 isomer has the characteristic of induced y emission by low-energy x rays has been a focus of attention for many scientists and researchers in recent decades. In this paper, an experiment regarding triggering 178Hfm2 emission decay is conducted at Shanghai Synchrotron Radiation Facility. An x-ray beam with 20.825-keV energy irradiates a rectangular sample containing about 1011178Hfm2 nuclides. By comparing the net gamma count rates during the irradiation with those after the irradiation, the data show that at the 426-, 495-, and 574-keV gamma lines, there is no significant enhancement, indicating that the induced y decay of 178Hfm2 has not been observed. [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]

Cross sections for the 174Hf(n, 2n)173 Hf and 176Hf(n, 2n)175Hf reactions have been measured on the 5.5-MV Van de Graaff tandem accelerator of National Centre for Scientific Research "Demokritos" in Athens, in the neutron energy region from 8.8 to 11.0 MeV, using the activation technique. An experimental method to account for the contamination of the 176Hf(n, 2n) reaction by the 176Hf(n, λ) reaction activated by the parasitic neutrons of the beam is presented. Statistical model calculations have also been performed using the nuclear-reaction codes EMPIRE-II and TALYS. The results and effects of the nuclear input parameters as well as pre-equilibrium emission are discussed in detail. [ABSTRACT FROM AUTHOR]

High-spin properties of the nucleus 117Hf were studied through the 128Te(48Ca,5n) reaction. Previously known bands have been extended to significantly higher spins and four new bands have been extracted from these data. The results are discussed within the framework of the cranked shell model aided by a comparison with level structures in the neighboring nuclei. The band crossings at rotational frequencies ∼500 keV are interpreted as caused by the alignments of h11/2 and h9/2 proton Orbitals. Band ED2 exhibits an alignment pattern similar to that of band EDI which was reported in a recent paper and proposed to be built on a second potential energy minimum involving the deformation-driving proton i13/2 ⊗ h19/2 configuration. It is likely that band ED2 is also associated with a deformation enhanced with respect to that of the normal deformed structures. Further experimental investigation is needed to ascertain the nature of this band. [ABSTRACT FROM AUTHOR]

Mean lifetimes of yrast states of the isotopes 174,176,178,180Hf have been measured using fast-electronic scintillation timing. Excited states of 174,176,178Hf were populated via β decay, while 180Hf was populated via Coulomb excitation. The lifetimes of the 2+1 and 4+1 states of all isotopes and the lifetimes of the 6+1 states of 174,178Hf were measured, using the slope and the centroid shift methods. The mean lifetime, τ(4+1)=85(13)ps, of 178Hf has been determined for the first time. In addition, the mean lifetimes of the 2-1 and the 3-1 states of 176Hf have been determined. Systematic uncertainties on the evolution of data as a function of neutron number were reduced by using the same setup for all the isotopes of interest. The data are in agreement with other recent lifetime measurements where available and shows a shift of the maximum of collectivity for the Hf isotopic chain from neutron midshell at N=104 to N=100. [ABSTRACT FROM AUTHOR]

The structures of yrast normal-deformed (ND) bands in Hf isotopes have been investigated using the unpaired cranked Nilsson-Strutinsky (CNS), and the paired cranked Nilsson-Strutinsky-Bogoliubov (CNSB) models. New optimized Nilsson parameters have been derived and used in the models to interpret the experimental data in 168-175Hf isotopes. The calculated kinematic moments of inertia, as well as the excitation energies of the yrast bands, have been compared with the experimental findings, and good agreements are observed. Configuration changes along the yrast lines have been traced by the aid of the CNS calculations. The calculated single-particle excitations shed more light on the nature of the crossings and successfully explain some features of the observed rotational bands which had not been clear before. [ABSTRACT FROM AUTHOR]

Multi-quasiparticle high-K states, several of which are isomeric, were observed in 180Hf with the Gammasphere array. Lifetimes in the ns-μs range were determined using centroid-shift and decay measurements within a μs coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to Kπ=(18-) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well. [ABSTRACT FROM AUTHOR]