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The recoil-β tagging technique was used to identify transitions associated with the decay of the 2+ and, tentatively, the 4+ excited states in 74Sr. Combining these results with published data for the A = 74 isobars, triplet energy differences (TEDs) have been extracted, the heaviest case for which these values have been evaluated. State-of-the-art shell-model calculations using the JUN45 interaction and incorporating a J = 0 isospin nonconserving (INC) interaction with an isotensor strength of 100 keV can reproduce the trend in the TED data, with particularly good agreement for the 2+ state. This agreement for the TED data taken together with the fact that agreement has also been shown between shell-model calculations with the same strength of INC interaction in the f7/2 shell and recently for A = 66 strongly suggests that such an interaction exists throughout the nuclear chart and cannot have a strong dependence on details of nuclear structure such as which nuclear orbitals are occupied. It also supports the hypothesis that only a J = 0 component of the INC interaction need be included to explain the observed TEDs. [ABSTRACT FROM AUTHOR]

Background: Two-photon emission, while well known in atomic physics, is arare second-order process in nuclear physics with only three cases where a two-photon branch is measured. The limited knowledge stems from the experimental difficulty in resolving two-photon emission from dominant single-photon emission, restricting practical cases for study to 0+ ⊿ 0+ (E0) transitions, since single-photon emission is forbidden. In practical terms, this limits the range of easily accessible cases to even-even nuclei with the unusual property of a first excited state with spin/parity of 0+. Purpose: Two-photon branches are measured for the closed-shell nuclei, 160,40Ca, and 90Zr. The intention of the present work was to obtain data for a case which was not a closed-shell nucleus. Of the possible nuclei relevant to such a study, 98Mo was chosen as its first-excited state is 0+ and lies below 1 MeV, meaning that internal pair transitions are not allowed. Method: The first excited state ( J = 0+) in 98Mo was excited in resonant inelastic proton scattering using a 6.7-MeV proton beam. The population of the state was selected using an annular double-sided silicon strip detector (DSSD). The decay of the state by conversion electrons was observed using the same DSSD, while Gammasphere was used to detect possible two-photon events. Results: An upper limit on the two-photon branch obtained was 1 x 10-4 at the 95% confidence level (CL). Conclusions The upper limit obtained is smaller than any other previously obtained two-photon branch. Phase space considerations suggest that the actual value of the branching ratio in this case may be significantly smaller than the upper limit obtained. [ABSTRACT FROM AUTHOR]

Candidates for three excited states in the 66Se have been identified using the recoil-ß tagging method together with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and triplet energy differences between analog states across the A = 66 triplet as a function of angular momentum. The extracted triplet energy differences follow the negative trend observed in the f7/2 shell. Shell-model calculations indicate that the strength of the Coulomb isotensor part alone is not sufficient to account for this trend in the case of the A = 66 triplet. [ABSTRACT FROM AUTHOR]

The article presents a comparison of mirror symmetry in the A = 23, T = 1/2 mirror nuclei 23Na and 23Mg both to high spin, and high excitation energy, including beyond the proton threshold. Excited states in the region above the proton threshold have been studied in both nuclei. It presents methods of obtaining reaction rates for nuclear astrophysics. It concludes that estimated data of shell model calculations can be used if real data is not available.

Recent antisymmetrized molecular dynamics (AMD) calculations for 28Si suggest the presence of a superdeformed (SD) band with a dominant 24Mg + α clustering for its configuration, with firm predictions for its location and associated moment of inertia. This motivates a review of the experimental results reported in the literature with a particular focus on 24Mg(α,γ) studies, as well as on a-like heavy-ion transfer reactions such as 12C(20Ne,α)28Si. Combining this information for the first time leads to a set of candidate SD states whose properties point to their α-cluster structure and strong associated deformation. Analysis of data from Gammasphere allows the electromagnetic decay of these candidate states to be probed and reveals further supporting evidence for such a structure. This paper appraises this body of information and finds the evidence for an SD band is strong. [ABSTRACT FROM AUTHOR]

The decay branchings of a resonance in the 12C(12C,γ)24Mg reaction at Ec.m = 8.0 MeV have been studied with high resolution using the Gammasphere array. Radiative capture residues were discriminated from scattered beam and the dominant evaporation channels using the fragment mass analyzer coupled to a multistage Parallel Grid Avalanche Counter (PGAC)/ion chamber system. The clean selection of residues has allowed the population of excited states up to 10 MeV in 24Mg to be examined in detail. Strong feeding of an excited Kπ = 0- band is observed. A Jπ = 4+ assignment to the resonance is strongly favored. [ABSTRACT FROM AUTHOR]

Background: Shape coexistence in heavy nuclei poses a strong challenge to state-of-the-art nuclear models, where several competing shape minima are found close to the ground state. A classic region for investigating this phenomenon is in the region around Z=82 and the neutron midshell at N=104. Purpose: Evidence for shape coexistence has been inferred from α-decay measurements, laser spectroscopy, and in-beam measurements. While the latter allow the pattern of excited states and rotational band structures to be mapped out, a detailed understanding of shape coexistence can only come from measurements of electromagnetic matrix elements. Method: Secondary, radioactive ion beams of 202Rn and 204Rn were studied by means of low-energy Coulomb excitation at the REX-ISOLDE in CERN. Results: The electric-quadrupole (E2) matrix element connecting the ground state and first excited 21+ state was extracted for both 202Rn and 204Rn, corresponding to B(E2;21+ → 01+)=29-8+8 and 43-12+17 W.u., respectively. Additionally, E2 matrix elements connecting the 21+ state with the 41+ and 21+ states were determined in 202Rn. No excited 0+ states were observed in the current data set, possibly owing to a limited population of second-order processes at the currently available beam energies. Conclusions: The results are discussed in terms of collectivity and the deformation of both nuclei studied is deduced to be weak, as expected from the low-lying level-energy schemes. Comparisons are also made to state-of-the-art beyond-mean-field model calculations and the magnitude of the transitional quadrupole moments are well reproduced. [ABSTRACT FROM AUTHOR]

The shape isomers of the 28Si nucleus are derived from Nilsson model calculations combined with quasidynamical SU(3) symmetry considerations, and their possible binary clusterizations are determined. The results are compared with those of other calculations. Concerning the superdeformed state our finding gives support to the new candidate suggested by Jenkins et al. [ABSTRACT FROM AUTHOR]

Background: Triplet energy differences (TED) can be studied to yield information on isospin-non-conserving interactions in nuclei. Purpose: The systematic behavior of triplet energy differences (TED) of T=1, Jπ=2+ states is examined. The A=62 isobar is identified as having a TED value that deviates significantly from an otherwise very consistent trend. This deviation can be attributed to the tentative assignments of the pertinent states in 62Ga and 62Ge. Methods: An in-beam γ-ray spectroscopy experiment was performed to identify excited states in 62Ga using Gamma-Ray Energy Tracking In-Beam Nuclear Array with the S800 spectrometer at NSCL using a two-nucleon knockout approach. Cross-section calculations for the knockout process and shell-model calculations have been performed to interpret the population and decay properties observed. Results: Using the systematics as a guide, a candidate for the transition from the T=1, 2+ state is identified. However, previous work has identified similar states with different Jπ assignments. Cross-section calculations indicate that the relevant T=1, 2+ state should be one of the states directly populated in this reaction. Conclusions: As spins and parities were not measurable, it is concluded that an unambiguous identification of the first T=1, 2+ state is required to reconcile our understanding of TED systematics [ABSTRACT FROM AUTHOR]

Lifetimes of low-lying excited states have been measured in 66Ge, 69Se, and 65Ga using a γ-ray lineshape method. The results confirm the previously reported 71- state lifetime in 66Ge. The lifetime of the yrast 5/2- state in 65Ga is measured for the first time. Lifetime measurements of two excited 3/2- states in 69Se are also reported. Two previously unobserved γ rays have been identified in 69Se. γ-γ coincidence measurements have been used to place one of these in the level scheme. 69Se excited state populations are compared to shell-model calculations using the GXPF1A interaction in the fp model space. Theoretical spectroscopic factors to excited states in 69Se have identified three candidate levels for the origin of one of the new transitions. [ABSTRACT FROM AUTHOR]

The heavy-ion radiative capture 12C(O16,γ28Si) was measured at the sub-Coulomb barrier bombarding energy Elab = 15.7 MeV, which corresponds to the lowest important resonance observed in the 12C+ O16 fusion excitation function. Thanks to combination of the bismuth germanate (BGO) γ-ray array and the 0° DRAGON electromagnetic spectrometer at TRIUMF, the γ-decay spectrum from the entrance channel down to the ground state of 28Si was measured. Comparisons of the experimental spectrum to γ spectrum extracted from Monte Carlo simulations of the complete setup suggest a Jπ = 2+ spin-parity assignment to the entrance channel and yield the radiative capture cross section ωRC = 0.22±0.04μb. Combining this present spin assignment with previous data on radiative capture, a J(J+1) systematics was constructed, and it indicated a moment of inertia commensurate with the 12C+O16 grazing angular momentum. Strong dipole transitions are observed from the entrance channel to T=1 states around 11.5 MeV and are found to result from enhanced M1IV transitions to states exhausting a large part of the M1 sum rule built on the ground state of 28Si. This specific decay was also reported at bombarding energies close to the Coulomb barrier in our previous study of the 12C(12C,γ24Mg) heavy-ion radiative capture reaction. Similarities between both systems are investigated. [ABSTRACT FROM AUTHOR]

An in-beam study has been performed to further investigate the known isomeric decays and to identify T = 1 excited states in the medium-heavy N = Z = 33 nucleus 66As. The fusion-evaporation reaction 40Ca(28Si,pn)66As was employed at beam energies of 75 and 83 MeV. The half-lives and ordering of two known isomeric states in 66As have been determined with improved accuracy. In addition, several prompt γ-ray transitions from excited states, both bypassing and decaying to the isomeric states in 66As, have been observed. Most importantly, candidates for the 4+ → 2+ and 6+ → 4+ transitions in the T = 1 band have been identified. The results are compared with shell-model calculations using the modern JUN45 interaction in the pf5/2g9/2 model space. [ABSTRACT FROM AUTHOR]

The high-spin structure of the nucleus 104Pd was studied through the 96Zr(13C,5rc) reaction at incident energies of 51 and 58 MeV, using the Euroball IV γ-ray spectrometer in conjunction with the DIAMANT charged-particle array. Several new medium- and high-spin bands were revealed. The already known positive-parity yrast and the negative-parity cascades were extended up to Ex ∼ 13, ∼ 11, and ∼9 MeV with Iπ = (26+), Iπ = (23-), and (20-), respectively. The deduced band structures were compared with Woods-Saxon total Routhian surface (TRS) calculations. In addition, non-yrast low-lying positive-parity bands were identified, which were assigned to soft γ-vibrational excitations. [ABSTRACT FROM AUTHOR]

The heavy-ion radiative capture reaction 12C(16O,γ)28Si has been studied at three energies Ec.m. = 8.5, 8.8, and 9 MeV which are close to the Coulomb barrier. The weak radiative capture process has been identified by measuring the 28Si recoils in the highly selective 0° spectrometer DRAGON at TRIUMF (Vancouver). The coincident γ rays have been recorded in the associated BGO array. This has allowed a complete measurement of the γ spectrum and the relative strength of all decay pathways. An important part of the decay through quasibound states close to the particle threshold and the feeding of bound states with particular deformation have been identified for the first time. Comparisons with Monte Carlo simulations allowed the extraction of the full experimental radiative capture cross section. Our results suggest an important contribution of spins Jπ = 5- and 6+ in the entrance channel. The surprisingly large cross sections from 12 μb at Ecm = 8.5 MeV to 25 μb at Ec.m.= 9.0 MeV for the heavy-ion radiative capture process are discussed in terms of the interplay between statistical and structural aspects of the process. [ABSTRACT FROM AUTHOR]

The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in 256Rf, which suggest that a long-lived, low-energy 8- isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a 256Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-μs isomer was identified. However, its low population, ∼5(2)% that of the ground state instead of the expected ∼30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z = 104, which describes nuclei with Z = 92-103 very well. [ABSTRACT FROM AUTHOR]