Showing papers by "R. Wadsworth published in 2005"

First evidence for chirality in Tc isotopes: Spectroscopy of 100Tc

Abstract: Excited states in 100Tc have been studied using the 96Zr( 7Li, 3n) reaction at a beam energy of 27 MeV. In the present work, evidence has been found for a second ΔI = 1 band decaying via several stretched dipole transitions to the previously known ΔI = 1 negative-parity band. Comparison of these data with those in neighbouring nuclei and also against recently reported criteria for chiral bands in nuclei, suggests that the two structures can be interpreted as chiral partners. Core quasi-particle coupling model calculations show reasonable agreement with the data and generally support the chiral interpretation of the states.

Evidence for chiral structures in 130Cs

Abstract: Two low lying positive-parity bands in 130Cs have been examined for chiral signatures. Small energy differences between the two bands, which have been previously observed, have been confirmed and the bands, as well as the number of transitions within and between the bands, extended. The intraband B(M1)/B(E2) ratios and B(M1)intraband/B(M1)interband ratios and the energy staggering parameter, S(I), have been deduced for these partner bands. The results are found to be consistent with a chiral interpretation for the two structures. Core–quasiparticle coupling model calculations have been performed to study 130Cs assuming a triaxial core. The experimental level energies and electromagnetic properties of the bands, resulting from the configuration, are reasonably well reproduced by the model, providing further evidence in support of the chiral interpretation of the two structures.

Investigation of antimagnetic rotation in light Cadmium nuclei: **106,108Cd

Abstract: The lifetimes of excited states belonging to the lowest lying positive-parity bands in {sup 106,108}Cd have been measured using the Doppler-shift attenuation method. The resulting B(E2) transition rates show a significant decrease with increasing spin in {sup 106}Cd, whereas in {sup 108}Cd there is tentative evidence for a similar effect. The results are compared with cranking and semiclassical model calculations, which indicate that the structures have the properties expected from an 'antimagnetic' rotational band resulting from the coupling of g{sub 9/2} proton holes to aligned pairs of h{sub 11/2} and g{sub 7/2} neutron particles.

Evidence for nontermination of rotational bands in Kr-74

Abstract: Three rotational bands in Kr-74 were studied up to (in one case one transition short of) the maximum spin I-max of their respective single-particle configurations. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin I-max. This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at I=I-max.

Evidence for oblate structure in Pb-186

Abstract: In-beam $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence data have been collected for $^{186}\mathrm{Pb}$ by combining the JUROGAM Ge-detector array and the GREAT spectrometer with the RITU gas-filled recoil separator for recoil-decay tagging measurements In addition to the known prolate yrast band in $^{186}\mathrm{Pb}$, these data have enabled a new low-lying side band to be identified Based on the analysis of its decay pattern and comparison with Interacting Boson Model (IBM) calculations, the new band is associated with an oblate shape

High-spin rotational structures in Kr-76

Abstract: High-spin states in Kr-76(36)40 have been populated in the Ca-40(Ca-40,4p)Kr-76 fusion-evaporation reaction at abeam energy of 165 MeV and studied using the Gammasphere and Microball multidetector arrays. The ground-state band and two signature-split negative parity bands of Kr-76 have been extended to similar to 30 (h) over bar. Lifetime measurements. using the Doppler-shift attenuation method show that the transition quadrupole moment of these three bands decrease as they approach their maximum-spin states. Two signatures of a new rotational structure with remarkably rigid rotational behavior have been identified. The high-spin properties of these rotational bands are analyzed within the framework of configuration-dependent cranked Nilsson-Strutinsky calculations. (Less)

First identification of excited states in 106Te and evidence for isoscalar-enhanced vibrational collectivity

Abstract: Gamma-ray transitions in the extremely neutron-deficient nucleus Te-106 have been identified for the first time. The experiment utilized the Fe-54(Fe-54,2n)Te-106(*) reaction, and the gamma-ray tra ...

High-spin structure of 102Ru

Abstract: High-spin states in the nucleus $^{102}\mathrm{Ru}$ have been investigated via the $^{96}\mathrm{Zr}$($^{13}\mathrm{C}$,\ensuremath{\alpha}3n) reaction at beam energies of 51 and 58 MeV, using the euroball IV \ensuremath{\gamma}-ray spectrometer and the diamant charged particle array. Several new high-spin bands have been established. The ground-state band has been extended up to ${E}_{x}~12$ MeV with ${I}^{\ensuremath{\pi}}=({26}^{+}$); the previously published negative-parity bands have been extended up to ${E}_{x}~11$ and \ensuremath{\sim} 9 MeV with ${I}^{\ensuremath{\pi}}=({23}^{\ensuremath{-}}$) and $({20}^{\ensuremath{-}})$, respectively. The deduced high-spin structure has been compared with Woods-Saxon total Routhian surface calculations and, on the basis of the measured Routhians, aligned angular momenta, and $B(M1)/B(E2)$ ratios, $\ensuremath{ u}{h}_{11/2}({g}_{7/2},{d}_{5/2}$) configurations are suggested for the negative-parity structures.

Quasi-γ band and odd-even staggering effect in 102 Ru

Abstract: Excited states of the nucleus $^{102}\mathrm{Ru}$ have been studied using the $^{96}\mathrm{Zr}$($^{10}\mathrm{B}$,$p3n$) reaction at a beam energy of $42\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The emitted \ensuremath{\gamma} rays were detected with the Gammasphere spectrometer. The known positive-parity structure built on the second ${2}^{+}$ state was extended up to the ${10}^{+}$ and ${11}^{+}$ states. This structure has been interpreted as a quasi-\ensuremath{\gamma} band. Its energy staggering as a function of spin has been analyzed in order to derive information on the type of triaxiality present in $^{102}\mathrm{Ru}$, a nucleus that serves as one of the cores for chiral structures in the mass $A\ensuremath{\approx}100$ region.

Recent progress on the investigation of spontaneous formation of chirality in rotating nuclei

Abstract: Experimental properties of nearly degenerate ΔI = 1 doublet bands, which are built on the same single-particle configuration, are tested against three criteria for spontaneous formation of chirality in nuclei via the coupling of three mutually perpendicular angular momenta. Four representative nuclei, 134 Pr, 130 Cs, 104 Rh and 105 Rh are discussed. The doublet bands in these nuclei exhibit chiral characteristics except for 134 Pr, which shows a significant difference in electromagnetic properties between the two candidate chiral structures.

Evidence for a new region of chirality around A ∼ 104

Abstract: Chirality in atomic nuclei is a direct consequence of the existence of triaxial nuclear shapes. This phenomenon is known to exist in the A ~ 130 region. We have now observed several pair of bands built upon the negative parity configuration, πg−19/2 ⊗ νh11/2, in Rh and Tc isotopes in the A ~ 104 region which can be understood in terms of the phenomenon of chiral symmetry breaking. Results of the search for chiral bands in 106Ag are presented in the current paper.

Lifetimes of high-spin states in Kr-76

Abstract: High-spin states in Kr-76(36)40 have been populated in the Ca-40 (Ca-40,4p) Kr-76 fusion-evaporation reaction at a beam energy of 165 MeV, and studied using the GAMMASPHERE and MICROBALL multi-detector arrays. The ground-state band and two signature-split negative-parity bands of Kr-76 have been extended to similar to 30h. Lifetime measurements using the Doppler-shift attenuation method indicate that the transition quadrupole moment of these three bands decrease as they approach their maximum-spin states.

Shape Coexistence In Light Krypton Isotopes

Abstract: Coexisting states of prolate and oblate shapes were studied via Coulomb excitation of radioactive 74Kr and 76Kr beams at safe energies at GANIL. The results for the transitional E2 matrix elements for several yrast transitions in both isotopes are in contradiction with the B(E2) values extracted from the lifetimes that are found in the literature. This motivated a new lifetime measurement which showed strong deviations from the previously published values, but is consistent with the results from Coulomb excitation. Having resolved these discrepancies and knowing the B(E2) values with high precision allows to extract the diagonal matrix elements from the Coulomb excitation data. The results confirm the proposed shape coexistence scenario.

Probing the three shapes in 186Pb using in-beam γ-ray spectroscopy

Abstract: This measurement represents the first observation of a non-yrast band in the 186Pb nucleus by employing the Recoil-Decay Tagging (RDT) technique. Previously known yrast levels have been confirmed and the band is extended up to level I π = (16+).