Observation of γ vibrations and alignments built on non-ground-state configurations in Dy 156

The exact nature of the lowest Kπ=2+ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ bands have been traced past the usual backbending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus Dy156, using the Nd148(C12,4n)Dy156 reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the Kπ=2+γ band are observed up to 32+ and 31+, respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ vibration built on the aligned yrast S band are observed up to spins 28+ and 27+. An even-spin positive-parity band, observed up to spin 24+, is a candidate for an aligned S band built on the seniority-zero configuration of the 02+ state at 676 keV. The crossing of this band with the 02+ band is at ?ωc=0.28(1)MeV and is consistent with the configuration of the 02+ band not producing any blocking of the monopole pairing

Investigation of negative-parity states in Dy 156: Search for evidence of tetrahedral symmetry

An experiment populating low/medium-spin states in Dy156 was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the Nd148(C12,4n) reaction and the Gammasphere array was utilized to detect the emitted γ rays. B(E2)/B(E1) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. In addition, several other negative-parity structures were observed to higher spin and two new sequences were established

Coexistence of a weakly-deformed band in a strongly-deformed nucleus

A weakly-deformed band J{sup {pi}} (E{sub x} keV) 0+ (1182), 2+ (1418), 4+ (1701) is identified in the strongly-deformed nucleus, {sup 154}Gd. Detailed {gamma}-ray spectroscopy following the beta decays of {sup 154}Eu (J = 3), {sup 154g,m1,m2}Tb (J = 0, 3, 7) are used to establish this structure. The structure is explained in terms of a pairing isomer which results from the {nu}[505] {up_arrow} Nilsson intruder orbital

Studies of the N=90 region: The decay of 154Eu to 154Gd

The decay of {sup 154}Eu {yields} {sup 154}Gd has been studied by {gamma}-ray singles and {gamma}-{gamma} coincidence spectroscopy using an array of 20 Compton-suppressed Ge detectors. The primary goal of the work was to confirm or refute a large number of questionable features in the decay scheme: the outcome is the removal of 8 levels from the previously adopted scheme, with the result that a new type of collective band is revealed. Many weak decay branches for the decay are clarified. These results are critical for understanding the structure of {sup 154}Gd and the N = 90 isotones; and the improved completeness of the decay scheme contributes to the use of {sup 154}Eu as a metrological standard

High-Statistics Study of the

A study of the 110In β+/EC decay was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) facility to probe the nuclear structure of 110Cd. The data were collected in scaled-down γ-ray singles, γ − γ coincidence, and γ-electron coincidence mode. The data were sorted and a random-background subtracted γ − γ matrix was created containing a total of 850 million events. We expanded the level scheme of 110Cd significantly by identifying 75 levels under 3.8 MeV, including 12 new ones, and increased the number of previously observed transitions from these levels to 273. The γ-ray branching intensities have been extracted through an analysis of the coincidence intensities. The branching ratios were combined with a reanalysis of lifetimes measurements obtained in an (n, n'γ) reaction with monoenergetic neutrons for the calculation of B(E2) values and these results have lead to the proposal of a γ-soft rotor, or O(6) nucleus, rather than a vibrational, or U(5) pattern for the nature of the low-lying, low-spin levels in 110Cd

Tests of the standard model from superallowed Fermi \mth{\beta}-decay studies: The \chem{^{74}Rb} \mth{\beta}-decay

Precise measurements of the intensities of superallowed Fermi $0^{+}\rightarrow{0}^{+}\beta$-decays have provided a powerful test of the CVC hypothesis at the level of $3\times10^{-4}$ and also led to a result in disagreement with unitarity for the CKM matrix at the 98% confidence level. It is essential to address possible trivial explanations for the apparent non-unitarity such as uncertainties in the isospin symmetry-breaking corrections. We have carefully studied the $^{74}$Rb$\rightarrow^{74}$Kr $\beta$-decay in order to measure the non-analog $\beta$-decay branching to the $0^{+}$ state at 508 keV in $^{74}$Kr. We have determined that this branching is $<3\times10^{-4}$, far smaller than any published theoretical estimate. We also show that high-precision, complete spectroscopy, measuring the major $\beta$-branches to excited $0^{+}$ and $1^{+}$ states, must be performed if one is to obtain a meaningful branching ratio to the excited $0^{+}$ state and concomitantly deal, in a substantial way, with the possibility of $\beta$ feeding to an array of $1^{+}$ states

Observation of γ vibrations and alignments built on non-ground-state configurations in Dy156

International audienceThe exact nature of the lowest Kπ=2+ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ bands have been traced past the usual backbending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus Dy156, using the Nd148(C12,4n)Dy156 reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the Kπ=2+γ band are observed up to 32+ and 31+, respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ vibration built on the aligned yrast S band are observed up to spins 28+ and 27+. An even-spin positive-parity band, observed up to spin 24+, is a candidate for an aligned S band built on the seniority-zero configuration of the 0+2 state at 676 keV. The crossing of this band with the 0+2 band is at ℏωc=0.28(1)MeV and is consistent with the configuration of the 0+2 band not producing any blocking of the monopole pairing