Based on a constituent quark model, spin-dependent and total photoabsorption cross sections are calculated in the low-energy range. The results are compared with recent data.

High-spin states in ${}^{162}$Lu and ${}^{164}$Lu have been studied by means of in-beam $\gamma$-ray spectroscopy techniques using the multidetector array GASP. The excited states have been populated through the ${}^{139}\mathrm{La}{(}^{28}\mathrm{Si}{,5n)}^{162}$Lu and ${}^{139}\mathrm{La}{[}^{29\left(30\right)\mathrm{}}\mathrm{Si},4\mathrm{}\left(5\right)n{]}^{164}$Lu reactions. Level schemes were constructed for both nuclei. Configurations for the rotational bands have been discussed. Alignments, band crossing frequencies, and $B\left(M1\mathrm{}\right)/B\left(E2\mathrm{}\right)\mathrm{}$ ratios have been analyzed in the framework of the cranking model. The systematic evolution of the signature inversion in the $\pi h_{11/2}\otimes \nu i_{13/2}$ structure is reviewed.

Excited states built on the ${13/2}^{+}$ isomers of the odd-mass ${}^{193,195,197}$Po isotopes have been observed via in-beam $\gamma$-ray spectroscopy. The $\alpha$ radioactivity of these isotopes has been used to tag $\gamma$-ray transitions following the ${}^A$Er+164 MeV ${}^{32}$S reactions, where $A=164\mathrm{}$, 166, 167, 168, and 170. Prompt $\gamma$ radiation was measured by ten Compton-suppressed Ge detectors at the target position and the Fragment Mass Analyzer was used to select evaporation residues. The results are compared with the first excited states of the heavier odd-mass polonium isotopes and of the even-mass cores.

The fusion-evaporation reaction ${}^{58}\mathrm{Ni}{(}^{32}\mathrm{S},2\mathrm{}\alpha p)$ has been used to study the neutron-deficient isotope ${}^{81}\mathrm{Y}.$ Multiple particle γ-ray coincidences have been detected by the GAMMASPHERE array combined with the MICROBALL charged-particle detector system. Gamma-ray spectra with an improved resolution have been achieved from an event-by-event determination of the nucleus recoil momentum, thus allowing a precise Doppler-shift correction. In this way a resolution enhancement by a factor 2 was obtained for a 1 MeV γ line. During the analysis an $E_{\gamma }{-E}_{\gamma }$ matrix as well as an $E_{\gamma }{-E}_{\gamma }{-E}_{\gamma }$ cube have been used to extend the previously known level scheme to higher spin $\left(I\approx \frac{57}{2}\right)$ and excitation energy ${(E}_x\approx 17\mathrm{MeV}).\mathrm{}$ More than 100 new γ rays and 80 new levels have been added to the level scheme and six new bands have been established. The interpretation of these bands in terms of the cranking model and their comparison with similar bands in neighboring nuclei is discussed.

β decay of the $T_z=-1/2$ nuclide ${}^{71}\mathrm{Kr}$ has been studied at the ISOLDE PSB Facility at CERN. ${}^{71}\mathrm{Kr}$ ions were produced in spallation reactions in a Nb foil using the 1 GeV proton beam and studied by means of β-delayed proton, β- and γ-ray spectroscopy. The half-life and the β-decay energy of ${}^{71}\mathrm{Kr}$ were determined using the decay of protons and positrons. These results: $T_{1/2}=100\mathrm{}\pm 3\mathrm{ms}$ and $Q_{\mathrm{EC}}=10.14\mathrm{}\pm 0.32\mathrm{}\mathrm{MeV}$ and the first observation of the β branch to the 207 keV level in ${}^{71}\mathrm{Br}$ makes the extension of the systematics of Gamow-Teller matrix elements of mirror nuclei up to $A=71\mathrm{}$ possible. The Gamow-Teller strength of the same magnitude as that of the $\mathrm{fp}$-shell mirror nuclei is observed for the ground-state transition.

We have used the ${}^{48}{\mathrm{C}\mathrm{a}+}^{176}\mathrm{Yb}$ reaction to study the population of high-spin states in neutron-rich nuclei by deep-inelastic reactions. Using Gammasphere, we observed gamma transitions from nuclei several neutrons richer than the target. Yrast states with spin up to 20 were populated in this reaction. High-spin states in ${}^{175,177,178}\mathrm{Yb}$ were observed. In this region of reduced pairing, a reference based on experimental data was used to derive experimental Routhians. Systematics of experimental Routhians in neutron-rich Yb nuclei compare well with cranked shell-model calculations.

Collective structures have been investigated via $\gamma$-ray studies in ${}^{117,119}$Sb. Previously observed strongly coupled $\left(\pi g_{9/2}\right)$${}^{-1}$ bands in both nuclei involving 1p-1h proton excitations across the $Z=50\mathrm{}$ gap have been extended, and an alignment of $h_{11/2}$ neutrons identified. New negative-parity strongly coupled bands based on this proton configuration have also been observed in both nuclei. Decoupled bands involving 2p-2h excitations across the gap have been observed in ${}^{119}$Sb, similar to those presented earlier for ${}^{117}$Sb. These bands are interpreted as due to the coupling of a low-$K$ valence proton to the $(\pi g_{7/2}{d}_{5/2}{)}^2\otimes (\pi g_{9/2}{)}^{-2}$ deformed state of the respective ${}_{50}$Sn core nuclei. Anomalies in the expected $h_{11/2}$ neutron crossing of these bands are discussed.

High-spin states in ${}^{77}$Kr were identified via analysis of prompt $\gamma$-$\gamma$ coincidences in the ${}^{58}$Ni${(}^{29}$Si,$2\alpha 2p)$ reaction at 128 MeV at the Gammasphere facility. Evaporation channel selection was achieved using the 95 element Microball charged-particle detector. 27 new states and 42 new transitions were found. The positive-parity bands were confirmed and the $\alpha =-$$\frac{1}{2}$ band extended to ${\frac{39}{2}}^{+}$. The negative-parity signature pair was extended to ${\frac{31}{2}}^{-}$ and ${\frac{37}{2}}^{-}$. Two new high-lying negative-parity bands were found extending from a state of spin $I=$$\frac{15}{2}$ and energy 2.6 MeV to 17.4 MeV at $I=\left(\frac{55}{2}\right)$. The new bands appear highly deformed and become yrast at high spin. A three-quasiparticle structure based on deformation driving, low-$K$ unique-parity and intruder orbitals is suggested for them.

The quasiparticle random-phase approximation (QRPA) is reviewed and higher-order approximations are discussed with reference to $\beta$-decay physics. The approach is fully developed in a boson formalism. Working within a schematic model, we first illustrate a fermion-boson mapping procedure and apply it to construct boson images of the fermion Hamiltonian at different levels of approximation. The quality of these images is tested through a comparison between approximate and exact spectra. Standard QRPA equations are derived in correspondence with the quasi-boson limit of the first-order boson Hamiltonian. The use of higher-order Hamiltonians is seen to improve considerably the stability of the approximate solutions. The mapping procedure is also applied to Fermi $\beta$ operators: exact and approximate transition amplitudes are discussed together with the Ikeda sum rule. The range of applicabilty of the QRPA formalism is analyzed.

We investigate the treatment of repulsive interactions in the presence of thermal fluctuations in hot finite systems, within the context of the static path approximation (SPA) and the ensuing SPA plus random-phase approximation treatment. We show that static repulsive variables can be correctly treated in the stationary-phase approximation. Results are shown for models containing both attractive and repulsive terms, where the accuracy of the previous methods and the effects of repulsive terms are analyzed.

The particle-hole and $\Delta$-hole excitations are well-known elementary excitation modes for the pion propagator in nuclear matter. But, the excitation also involves antiparticles, namely, nucleon-antinucleon, anti-$\Delta$-nucleon and $\Delta$-antinucleon excitations. These are important for high-energy momentum as well, and have not been studied before, to our knowledge. In this paper, we give both the formulas and the numerical calculations for the real and the imaginary parts of these excitations.

The relation between Galilei invariance and the energy weighted sum rule for a mass dipole operator is discussed using a monopole pairing interaction. It is found that the energy weighted sum rule for the mass dipole operator changes as much as 18% in medium and heavy nuclei.

Theoretical results on the ground-state properties of the hypothetical spherical superheavy atomic nuclei are presented and discussed. Even-even isotopes of elements $Z=104\mathrm{}-120$ are considered. Certain conclusions are also drawn for odd-$A$ and odd-odd superheavy nuclei. Results obtained earlier for even-even deformed superheavy nuclei with $Z=104\mathrm{}-114$ are given for completeness. Equilibrium deformation, nuclear mass, $\alpha$-decay energy, $\alpha$-decay half-life, dynamical fission barrier, as well as spontaneous-fission half-life are considered. $\beta$-stability of superheavy nuclei is also discussed. The calculations are based on the macroscopic-microscopic model. A multidimensional deformation space describing axially symmetric nuclear shapes is used in the analysis of masses and decay properties of superheavy nuclei. We determined the boundaries of the region of superheavy nuclei which are expected to live long enough to be detected after the synthesis in a present-day experimental setup.

The nearest-neighbor-spacing distribution and the cumulative spacing distribution of the low-lying energy levels of ${}^{26}$Al are analyzed with isospin considered as a good symmetry, taking into account that the pure isospin sequence is not fully chaotic. Levels with isospin zero are found well represented by a formula, recently suggested for systems having mixed regular-chaotic dynamics, with the regular motion occupying 10% of the classical phase space. When levels with isospins zero and one are together considered, the spacing distribution agrees, within the experimental uncertainties, with that of a superposition of two sequences of independent levels without introducing isospin mixing.

It was recently demonstrated that the empirical linear correlation of ${E(4\mathrm{}}_1^{+})$ with ${E(2\mathrm{}}_1^{+})$ is reproduced by the interacting boson model 1 (IBA-1) if a constant value for the coefficient $\kappa$ of the Q$\cdot$Q term is used. This constancy motivates the present investigation of whether it is possible to find sets of IBA-1 parameters, with fixed $\kappa$, that reproduce the data for a more general set of observables and a wide range of nuclei. A consistent procedure, based on contour plots of key observables, was used to extract $\epsilon$ and $\chi$ values for 145 nuclei spanning the $Z$ = 50–82 shell, which give reasonable overall agreement with the data with smoothly varying parameters. The constant $\kappa$ constraint sometimes leads to parameter values different than normal: finite $\epsilon$ values $(\sim$ 0.1 MeV) even for rotational nuclei and large $\chi$ values for transitional and vibrational nuclei that even increase towards the vibrational region. Finally, a systematic correlation of $\epsilon$ values with ${E(2\mathrm{}}_1^{+})$ was found.

We derive large-amplitude collective equations of motion from the variational principle for the time-dependent Schrödinger equation. These equations reduce to the well-known diabatic formulas for vibrational frequencies in the small-amplitude limit. The finite-amplitude expression allows departures from the harmonic behavior of giant resonances to be simply estimated. The relative shift of the second phonon falls with nuclear mass $A$ as $A^{-4/3}$ in the three modes we consider: monopole, dipole, and quadrupole. Numerically, the effect is very small in heavy nuclei, as was found with other approaches.

The strength distributions of Gamow-Teller (GT) transitions from ${}^{11}\mathrm{Li}$ and ${}^{12}\mathrm{Be}$ are investigated. We study where the GT strengths of the transitions ${}^{11}\mathrm{Li}$ ${(3/2\mathrm{}}_{\mathrm{gs}}^{\mathrm{-}}{)\to }^{11}{\mathrm{Be}}^{*}$ (${1/2}^{-},$ ${3/2}^{-},$ ${5/2}^{-}$) are located incorporating quenching effects due to the Δ-hole contributions. The connection between the GT sum rule and effects of the halo structure of ${}^{11}\mathrm{Li}$ are discussed. The narrowing of the gap between the $p$ shell and the $\mathrm{sd}$ shell is found to change the structure of the GT strength distribution. The accuracy of the present calculation is tested for the GT decay from ${}^9\mathrm{Li}.$ We further study the GT transition from ${}^{12}\mathrm{Be}.$ The narrowing of the gap between the $p$ and $\mathrm{sd}$ shells varies the transition strength to ${}^{12}\mathrm{Be}$ ${(1\mathrm{}}_{\mathrm{gs}}^{+})$ as well as the GT distribution. The quenching of the transition strength ${}^{12}{\mathrm{Be}\to }^{12}\mathrm{B}$ ${(1\mathrm{}}_{\mathrm{gs}}^{+})$ suggests an enormous breaking of the neutron closed-shell structure of ${}^{12}\mathrm{Be}.$

We propose a numerical algorithm for finding periodic solutions of the time-dependent Hartree-Fock equations. We show that this algorithm preserves the particle number and the total energy exactly. We demonstrate the method by calculating the periodic breathing mode of ${}^4\mathrm{He}.$ We discuss the generalization to more realistic cases, including multidimensional periodic modes.

We present an analytical proof and a generalization of the Fayache-Sharon-Zamick relation between single particle energy splittings and the SU(3) limit in Elliott’s model.

Measurements of fission fragment gamma ray multiplicity distributions were carried out at near and sub-barrier energies in ${}^{12}$C, ${}^{16}$O + ${}^{232}$Th reactions. The results were analyzed to determine the average values of the total fragment spin, which were used to deduce the average spin of the compound nucleus $〈l{〉}_{\mathrm{CN}}.$ It is observed that $〈l{〉}_{\mathrm{CN}}$ decreases smoothly with decreasing bombarding energy and saturates as the energy falls through the barrier, thereby resembling features analogous to those predicted by various fusion models. The present results do not indicate any anomalous feature in the $〈l{〉}_{\mathrm{CN}\mathrm{}}$ at the sub-barrier energies, which imply that the recently observed anomalous fragment anisotropies in these systems are not due to anomalous broadening of fusion $l$ distributions but may result from the narrowing of $K$ distribution in the fission process.