Showing papers by "R. Wadsworth published in 2010"

Shape coexistence at the proton drip-line: First identification of excited states in Pb180

Abstract: Excited states in the extremely neutron-deficient nucleus {sup 180}Pb have been identified for the first time using the JUROGAM II array in conjunction with the RITU recoil separator at the Accelerator Laboratory of the University of Jyvaeskylae. This study lies at the limit of what is presently achievable with in-beam spectroscopy, with an estimated cross section of only 10 nb for the {sup 92}Mo({sup 90}Zr,2n){sup 180}Pb reaction. A continuation of the trend observed in {sup 182}Pb and {sup 184}Pb is seen, where the prolate minimum continues to rise beyond the N=104 midshell with respect to the spherical ground state. Beyond-mean-field calculations are in reasonable correspondence with the trends deduced from experiment.

High-energy excited states in 98Cd

Abstract: In 98Cd a new high-energy isomeric γ-ray transition was identified, which confirms previous spin-parity assignments and enables for the first time the measurement of the E2 and E4 strength for the two decay branches of the isomer. Preliminary results on the 98Cd high-excitation level scheme are presented. A comparison to shell-model calculations as well as implications for the nuclear structure around 100Sn are discussed.

Lifetimes of odd-spin yrast states in 182 Hg

Abstract: Lifetimes of excited states in $^{182}\mathrm{Hg}$ were extracted from recoil-gated $\ensuremath{\gamma}$-ray spectra and recoil-gated $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence matrices using the recoil distance Doppler-shift method. States were populated using the $^{96}\mathrm{Mo}$($^{88}\mathrm{Sr}$,$2n$)$^{182}\mathrm{Hg}$ fusion-evaporation reaction. Measured lifetimes allowed transition probabilities, transition quadrupole moments, quadrupole deformation parameters, and transition dipole moments to be deduced for the band formed by the odd-spin yrast states. The experimental results confirm the low degree of octupole collectivity in this mass region.

Observation of a New High-spin Isomer in 94Pd

Abstract: A second gamma-decaying high-spin isomeric state, with a half-life of 197(22) ns, has been identified in the N = Z + 2 nuclide Pd-94 as part of a stopped-beam Rare Isotope Spectroscopic INvestigation at GSI (RISING) experiment. Weisskopf estimates were used to establish a tentative spin/parity of 19(-), corresponding to the maximum possible spin of a negative parity state in the restricted (p(1/2), g(9/2)) model space of empirical shell model calculations. The reproduction of the E3 decay properties of the isomer required an extension of the model space to include the f (5/2) and p(3/2) orbitals using the CD-Bonn potential. This is the first time that such an extension has been required for a high-spin isomer in the vicinity of Sn-100 and reveals the importance of such orbits for understanding the decay properties of high-spin isomers in this region. However, despite the need for the extended model space for the E3 decay, the dominant configuration for the 19(-) state remains (p p(1/2)(-1)g(9/2)(-3))(11)circle times(nu g(9/2)(-2))(8). The half-life of the known, 14(+), isomer was remeasured and yielded a value of 499(13) ns.

Two-Particle Separation Energy Trends in the Superdeformed Well

Abstract: A measurement of the energy and spin of superdeformed states in {sup 190}Hg, obtained through the observation of transitions directly linking superdeformed and normal states, expands the number of isotopes in which binding energies at superdeformation are known. Comparison with neighboring nuclei shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the lower Coulomb barrier and lower total binding energy. This unexpected result provides a critical test for nuclear models.

High-spin intruder band in In-107

Abstract: High-spin states in the neutron-deficient nucleus In-107 were studied via the Ni-58(Cr-52,3p) reaction. In-beam gamma rays were measured using the JUROGAM detector array. A rotational cascade consisting of ten gamma-ray transitions, which decays to the 19/2(+) level at 2.002 MeV, was observed. The band exhibits the features typical for smooth terminating bands that also appear in rotational bands of heavier nuclei in the A similar to 100 region. The results are compared with total Routhian surface and cranked Nilsson-Strutinsky calculations.

Evidence of nontermination of collective rotation near the maximum angular momentum in Rb75

Abstract: Two of the four known rotational bands in {sup 75}Rb were studied via the {sup 40}Ca({sup 40}Ca,{alpha}p){sup 75}Rb reaction at a beam energy of 165 MeV. Transitions were observed up to the maximum spin I{sub max} of the assigned configuration in one case and one-transition short of I{sub max} in the other. Lifetimes were determined using the residual Doppler shift attenuation method. The deduced transition quadrupole moments show a small decrease with increasing spin, but remain large at the highest spins. The results obtained are in good agreement with cranked Nilsson-Strutinsky calculations, which indicate that these rotational bands do not terminate, but remain collective at I{sub max}.

Non-termination of yrast bands at maximum configuration spin in Kr73

Abstract: High-spin states in $^{73}\mathrm{Kr}$ were studied at the XTU tandem accelerator of the Laboratori Nazionali di Legnaro using the reaction $^{40}\mathrm{Ca}$($^{40}\mathrm{Ca}$,$\ensuremath{\alpha}2\mathit{pn}$) at a beam energy of 185 MeV. Gamma rays were detected with the EUROBALL spectrometer. Particle detection enabled us to identify the reaction channel leading to $^{73}\mathrm{Kr}$. The yrast bands of positive and negative parity were established up to probable spins of $61/{2}^{+}$ and $63/{2}^{\ensuremath{-}}$, respectively. The energies of the two identified bands agree well with the predictions of the configuration-dependent Cranked Nilsson-Strutinsky approximation and indicate that the nucleus remains collective up to the maximum spins of the respective high-spin configurations. The positive-parity band represents one of the rare cases where band non-termination at the highest spin of the configuration could be established experimentally.

High-spin intruder band in 107In

Abstract: High-spin states in the neutron-deficient nucleus 107 In were studied via the SB Ni (52Cr,3p) reaction. In-beam γ rays were measured using the JUROGAM detector array. A rotational cascade consisting of ten γ-ray transitions, which decays to the 19/2 + level at 2.002 MeV, was observed. The band exhibits the features typical for smooth terminating bands that also appear in rotational bands of heavier nuclei in the A ~ 100 region. The results are compared with total Routhian surface and cranked Nilsson-Strutinsky calculations.

First Gamma-Ray Spectroscopy and Isospin Symmetry Study of the N = Z-2 Nucleus V-44

Abstract: Excited states in the T-z = -1 nucleus V-44 have been observed for the first time. The states have been identified through recoil-gamma-gamma coincidences and comparison with analogue states in the mirror nucleus Sc-44. Mirror energy differences have been extracted and compared to state-of-the-art fp shell-model calculations which include charge symmetry breaking forces.