A superdeformed rotational band has been identified in 36Ar, linked to known low-spin states, and observed to its high-spin termination at Ipi = 16(+). Cranked Nilsson-Strutinsky and spherical shell model calculations assign the band to a configuration in which four pf-shell orbitals are occupied, leading to a low-spin deformation beta(2) approximately 0.45. Two major shells are active for both protons and neutrons, yet the valence space remains small enough to be confronted with the shell model. This band thus provides an ideal case to study the microscopic structure of collective rotational motion.
A new experimental technique is presented using proton-γ-γ correlations from (94)Mo(d,p)(95)Mo reactions which allows for the model-independent extraction of the photon strength function at various excitation energies using primary γ-ray decay from the quasicontinuum to individual low-lying levels. Detected particle energies provide the entrance excitation energies into the residual nucleus while γ-ray transitions from low-lying levels specify the discrete states being fed. Results strongly support the existence of the previously reported low-energy enhancement in the photon strength function.
Lifetimes of states in the triaxial strongly deformed bands of 163 Lu have been measured with the Gammasphere spectrometer using the Doppler-shift attenuation method. The bands have been interpreted as wobblingphonon excitations from the characteristic electromagnetic properties of the transitions connecting the bands. Quadrupole moments are extracted for the zero-phonon yrast band and, for the first time, for the one-phonon wobbling band. The very similar results found for the two bands suggest a similar intrinsic structure and support the wobbling interpretation. While the in-band quadrupole moments for the bands show a decreasing trend towards higher spin, the ratio of the interband to the in-band transition strengths remains constant. Both features can be understood by a small increase in triaxiality towards higher spin. Such a change in triaxiality is also found in cranking calculations, to which the experimental results are compared.
Triaxial-rotor-plus-particle model calculations strongly support a pure axially-symmetric shape with large quadrupole deformation in Y isotopes.
Excited states in the neutron-rich N ¼ 38, 36 nuclei 60 Ti and 58 Ti were populated in nucleon-removal reactions from 61 V projectiles at 90 MeV=nucleon. The γ-ray transitions from such states in these Ti isotopes were detected with the advanced γ-ray tracking array GRETINA and were corrected event by event for large Doppler shifts (v=c ∼ 0.4) using the γ-ray interaction points deduced from online signal decomposition. The new data indicate that a steep decrease in quadrupole collectivity occurs when moving from neutron-rich N ¼ 36, 38 Fe and Cr toward the Ti and Ca isotones. In fact, 58;60 Ti provide some of the most neutron-rich benchmarks accessible today for calculations attempting to determine the structure of the potentially doubly magic nucleus 60 Ca. DOI: 10.1103/PhysRevLett.112.112503 PACS numbers: 23.20.Lv, 21.60.Cs, 27.30.+t, 29.38.Db One of the main goals of nuclear physics is the development of a predictive model for the properties of all nuclei, including the shortest-lived species in as yet unexplored regions of the nuclear chart. This is important, for example, in the quest to understand the origin of the elements in the Universe since many nucleosynthesis processes involve nuclei far removed from the valley of β stability. One of the cornerstones in the description of nuclear properties is nuclear shell structure-whereby discrete nucleon singleparticle orbitals are clustered in energy, resulting in stabilizing energy gaps occurring for certain "magic" proton or neutron numbers. Doubly magic nuclei, with both proton and neutron magic numbers, are particularly important for the development of nuclear models as they serve as essentially inert cores, reducing the many-body problem to that of the set of "valence nucleons" outside this core. However, modifications of shell structure have already been observed in short-lived nuclei with extreme neutron-to-proton ratios, with new shell gaps developing and some of the canonical magic numbers disappearing [1][2][3][4]. Considerable experimental and theoretical efforts are aimed at describing the physics driving such changes which are revealed most clearly on the neutron-rich side of the nuclear chart.Data for chains of proton-magic isotopes and regions of rapid shell evolution offer (complementary) challenging tests of nuclear models, allowing changes in nuclear structure to be tracked as a function of isospin and providing demanding benchmarks for calculations incorporating new physics effects. The chain of Ca isotopes (with magic proton number Z ¼ 20) and the region of neutron-rich nuclei near N ¼ 40, which are subject to rapid shell and shape changes [5][6][7][8][9], coincide at 60 Ca. In addition to the first spin-orbit driven neutron subshell closure at N ¼ 28 48 Ca, the neutron-rich Ca isotopes exhibit two additional subshell gaps at N ¼ 32 [10] and N ¼ 34 [11], attributed in part to the action of the monopole parts of the proton-neutron tensor force in the regime of large neutron excess [12,13].Nothing is known experimentally about the properti...
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