.
A new experimental setup to measure prompt-delayed
γ
-ray coincidences from isotopically identified fission fragments, over a wide time range of 100ns-200μ s, is presented. The fission fragments ...were isotopically identified, on an event-by-event basis, using the VAMOS++ large acceptance spectrometer. The prompt
γ
rays emitted at the target position and corresponding delayed
γ
rays emitted at the focal plane of the spectrometer were detected using, respectively, thirty two crystals of the AGATA
γ
-ray tracking array and seven EXOGAM HPGe Clover detectors. Fission fragments produced in fusion and transfer-induced fission reactions, using a
238
U beam at an energy of 6.2 MeV/u impinging on a
9
Be target, were used to characterize and qualify the performance of the detection system.
The B(E2, 2+ → 0+) transition strengths of the T=1 isobaric triplet 70Kr, 70Br, 70Se, recently measured at the RIKEN Radioactive Isotope Beam Factory (RIBF), are discussed in terms of ...state-of-the-art large scale shell model calculations using the JUN45 and JUN45 + LNPS plus Coulomb interactions. In this Letter we argue that, depending on the effective charges used, the calculations are either in line with the experimental data within statistical uncertainties, or the anomaly happens in 70Br, rather than 70Kr. In the latter case, we suggest that it can be due to the presence of a hitherto undetected 1+ T = 0 state below the yrast 2+ T = 1 state. Furthermore, our results do not support a shape change of 70Kr with respect to the other members of the isobaric multiplet.
The nature of the nuclear pairing condensates in heavy nuclei, specifically neutron-proton (spin-triplet), versus identical-particle (spin-singlet) pairing has been an active area of research for ...quite some time. In this work, we probe three candidates that should display spin-triplet, spin-singlet, and mixed-spin pairing. Using theoretical approaches such as the gradient method and symmetry-restoration techniques, we find the ground state of these nuclei in Hartree–Fock–Bogoliubov theory and compute ground state to ground state pair-transfer amplitudes to neighboring isotopes while simultaneously projecting to specific particle number and nuclear-spin values. We identify specific reactions for future experimental research that could shed light on spin-triplet and mixed-spin pairing.
The Shears Mechanism in Nuclei Clark, R. M.; Macchiavelli, A. O.
Annual review of nuclear and particle science,
01/2000, Letnik:
50, Številka:
1
Journal Article
Recenzirano
Odprti dostop
▪ Abstract This chapter reviews the experimental properties of shears bands. The most puzzling characteristic of these structures is the emergence of rotational-like behavior while the nucleus ...retains a small quadrupole deformation. Regardless of the details of particular theoretical models, it can be shown that the most important degree of freedom in describing the shears mechanism is the shears angle. It is then possible to develop a semiclassical description of the shears mechanism, in which the nature (multipole order) of the interaction between valence protons and neutrons constituting the shears “blades” may be derived and the dynamics of the system described. We discuss the competition between the shears mechanism and collective rotation and mention the connection to “magnetic rotation.” Directions for future theoretical and experimental efforts are suggested.
The spectroscopic quadrupole moment of the first 2+ state of 12C has been measured employing the Coulomb-excitation re-orientation technique. Our result of Qs(21+)=+9.3−3.8+3.5efm2 suggests a larger ...oblate deformation than previously reported. Combining this with the consistently re-analyzed adopted value, we present the most precise value to date of Qs(21+)=+9.5(18)efm2, which is consistent with a geometrical rotor description. This simple outcome is compared to state-of-the-art shell-model, mean-field, ab initio calculations, cluster-based and geometrical-like theories, which show varying degrees of emergent quadrupole collectivity.
The recent experimental observation of isospin symmetry breaking (ISB) in the ground states of the T=3/2 mirror pair 73Sr-73Br is theoretically studied using large-scale shell-model calculations. The ...large valence space and the successful PFSDG-U effective interaction used for the nuclear part of the problem capture possible structural changes and provide a robust basis to treat the ISB effects of both electromagnetic and nonelectromagnetic origin. The calculated shifts and mirror-energy differences are consistent with the inversion of the Iπ=1/2-,5/2- states between 73Sr-73Br and suggest that the role played by the Coulomb interaction is dominant. Finally, an isospin breaking contribution of nuclear origin is estimated to be ≈25keV.
The γ-ray tracking array GRETINA was coupled to the S800 magnetic spectrometer for spectroscopy with fast beams of rare isotopes at the National Superconducting Cyclotron Laboratory on the campus of ...Michigan State University. We describe the technical details of this powerful setup and report on GRETINA's performance achieved with source and in-beam measurements. The γ-ray multiplicity encountered in experiments with fast beams is usually low, allowing for a simplified and efficient treatment of the data in the γ-ray analysis in terms of Doppler reconstruction and spectral quality. The results reported in this work were obtained from GRETINA consisting of 8 detector modules hosting four high-purity germanium crystals each. Currently, GRETINA consists of 10 detector modules.
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