[en] The systematics of the (E2) #betta# ray transition energies and the available lifetime data are used to characterize the excitation modes of the light rare-earth nuclei (N greater than or equal to 82) at different spins. The results, which include our recently obtained data on ₁₄₉Gd, ₁₅₄Ho, ₁₅₅Er, ₁₅₇Yb and ₁₅₈Yb nuclei, indicate that, at low spins, the nuclear excitation mode (shapes) change from single-particle excitations (weakly oblate) in N less than or equal to 85 nuclei to quasi-vibrational (soft triaxial) in N = 86, weakly rotational (prolate) in N = 87, and rotational (prolate) in the N greater than or equal to 88 systems. At higher angular momenta, all these nuclei show a general tendency to traverse the (epsilon,#betta#) plane towards the oblate axis, and to eventually adopt the aligned coupling mode of excitation

[en] Two important developments in the sixties, namely the advent of heavy-ion accelerators and fabrication of Ge detectors, opened the way for the experimental studies of nuclear properties at high angular momentum. Addition of a new degree of freedom, namely spin, made it possible to observe such fascinating phenomena as occurrences and coexistence of a variety of novel shapes, rise, fall and occasionally rebirth of nuclear collectivity, and disappearance of pairing correlations. Today, with the promise of development of radioactive ion beams (RIB) and construction of the third-generation Ge-detection systems (GAMMASPHERE and EUROBALL), the authors are poised to explore new and equally fascinating phenomena that have been hitherto inaccessible. With the addition of yet another dimension, namely the isospin, they will be able to observe and verify predictions for exotic shapes as varied as rigid triaxiality, hyperdeformation and triaxial octupole shapes, or to investigate the T = 0 pairing correlations. In this paper, they shall review, separately for neutron-deficient and neutron-rich nuclei, these and a few other new high-spin physics opportunities that may be realized with RIB. Following this discussion, they shall present a list of the beam species, intensities and energies that are needed to fulfill these goals. The paper will conclude with a description of the experimental techniques and instrumentations that are required for these studies

[en] We investigated a new continuum γ-ray spectroscopy technique which is based on the detection of all emitted γ rays in a 4π detector system, and ordering them according to their energies on an event-by-event basis. The technique allows determination of growth strength functions, and rotational damping width as a function of spin and temperature. Thus, it opens up the possibility of studying the onset of motional narrowing and the mapping of the evolution of nuclear collectivity with spin and temperature. Application of the technique for preferential entry-state population, exit-channel selection, and feeding of the discrete states via selective pathways will be discussed. 19 refs., 6 figs

[en] The advent of large Ge arrays and their ancillary detectors has greatly advanced spectroscopic studies of the medium-mass nuclei. These nuclei undergo rapid shape changes as a function of spin, excitation energy and particle number and, thus, provide a unique laboratory to test and refine a variety of theoretical models. Following a brief review of the physics motivation, some of the highlights of the experimental results obtained with the help of these powerful detector systems will be discussed. Among results presented here are the newly-discovered island of superdeformation in the A∼80 mass region, and the high-spin band structures in the N∼Z nuclei. These band structures may be understood in the framework of the conventional cranking models, without the introduction of additional T=0 neutron-proton pairing correlations

[en] At ORNL, we have recently utilized the Spin Spectrometer setup to investigate the differential effects of increasing spin and excitation energy on nuclear shape and collectivity in ¹⁵⁸Yb. Along the yrast line of this and other N = 88 nuclei, weakly prolate shapes gradually give way to triaxial, and then finally to non-collective oblate shapes as the spin approaches 40 h-bar. However, above the yrast line, large deformation and collectivity once again sets in. This is evidenced by the emergence of a broad quadrupole structure (E/sub γ/ ≅ 1.2 MeV) in the continuum gamma-ray spectra that grows with increasing temperature. The short (sub ps) lifetimes of these transitions attest to the collective nature of these structures. The emergence and growth of the quadrupole structure at high excitation energies is closely correlated with the appearance of energetic (E/sub γ/ ≅ 2.5 MeV), fast M1 transitions which form another broad structure in the continuum spectra. From the centroid of the M1 bump, a quadrupole deformation parameter of 0.35 is inferred. Because of this sensitivity, these energetic M1 transitions provide a unique probe of nuclear shape in the excitation energy range of ≅ 3 to 10 MeV. 6 refs., 2 figs

[en] In the past few years, we have utilized the Spin Spectrometer and a variety of complementary probes (continuum γrays, proton-γ coincidence spectroscopy and γ decay of GDR) to study the nuclear response to the DIFFERENTIAL effects of increasing spin and temperature for constant values of excitation energy or spin, respectively. In this paper we shall describe two of the experiments that trace the properties of rapidly-rotating nuclei at small to moderate excitation energies. 22 refs., 7 figs

[en] Study of the finite-temperature effects in nuclear systems remain one of the least explored subjects in low-energy nuclear physics, despite the fact that dramatic structural changes are expected to unfold as the excitation energy of the system is increased. Gradual vanishing of the pairing correlations, onset of chaos and rotational damping, prolate-to-oblate shape changes, melting of the shell effects, and eventually the inability of the compound nucleus (CN) to sustain giant resonances at very high temperatures (''death'' of CN) are only a few examples of the rich and varied phenomena yet to be explored. Equally important is the question of thermal fluctuations and the extent to which they modify the above phase transitions. However, a prerequisite to the study of these fascinating questions is a detailed understanding of the formation and decay modes of compound nucleus which is astonishingly, lacking at present. In this chapter we shall discuss some recent experimental and theoretical developments that (a) raise new questions about these pivotal issues, and (b) provide clues and directions toward their resolution. They include questions of equilibration of CN (entrance-channel effects in fusion reactions, and structural effects in evaporation-proton spectra), and variations of the gamma strength functions with spin and temperature which directly affect deexcitation of CN following particle emission

[en] The purpose of this commentary is to briefly review several works on nuclear structure and to enumerate a few of the difficulties encountered in the interpretation of the experimental results. To be brief, comments are confined to the studies in the particle-bound regime, i.e., a temperature range of T ≤ 1 MeV. Among the interesting topics to be addressed in this temperature range are the question of thermal fluctuations, and the variations of the pairing correlations, shape parameters, nuclear collectivity, and rotational damping width with spin and excitation energy

[en] The aim of the present work was to determine a consistent set of single-particle energies and two-body interaction matrix elements that are relevant in the region around ¹⁴⁶Gd nucleus. The resulting values were used to calculate the medium- and high-spin states that are fed by the decay of the 550 ns isomer in ¹⁴⁷Gd. 5 refs., 1 fig., 6 tabs

[en] Some of the considerations on how to effectively incorporate bismuth germanate into complex detection systems are covered, and some of these new systems now in operation or under construction are discussed. Significant achievements in gamma ray spectroscopy are reviewed as well as some recent results based on data taken with coincidence arrays of germanium detectors and Compton-suppression spectrometers. Then the first impact of bismuth germanate detectors on our understanding of the properties of nuclei that have high energy and very high angular momentum states are addressed