High-spin states in ${}^{77}$Se were studied using the ${}^{76}$Ge$(\alpha$,$3n)$ reaction at 40 MeV at the Florida State University Tandem-LINAC facility. Prompt $\gamma$-$\gamma$ coincidences were observed using the Pitt-FSU detector array. The positive- and negative-parity yrast bands were extended up to spins of (${\frac{31}{2}}^{+}$) and (${\frac{27}{2}}^{\mathrm{-}}$), respectively. Spin assignments were made based on directional correlation of oriented nuclei ratios whenever possible. A rich and complicated high-lying high-$K$ negative-parity structure was also found. The positive-parity yrast structure shows a change from large signature splitting at low spin to a more uniform level spacing at higher spins, as has been seen in the heavier $N=43\mathrm{}$ isotones. Theoretically, this change is attributed to a shift from oblate to triaxial shape due to the alignment of a pair of $g_{9/2}$ protons.

The proton momentum and density distributions of closed shell nuclei are calculated with a model treating short-range correlations up to first order in the cluster expansion. The validity of the model is verified by comparing the results obtained using purely scalar correlations with those produced by finite nuclei Fermi hypernetted chain calculations. State dependent correlations are used to calculate momentum and density distributions of ${}^{12}$C, ${}^{16}$O, ${}^{40}$Ca, and ${}^{48}$Ca, and the effects of their tensor components are studied.

We present a stochastic method of minimizing the ground state energy in variational calculations of light nuclei using the refined resonating group model. The method utilizes a bit representation of the width parameters to be varied. To find the best possible set of width parameters we use strategies familiar from biological evolution. Very complicated problems can be solved in this way because the method is intrinsically parallel. The algorithm can be used on parallel computers with any number of processors without any change. As an example we give the results of a simple model calculation of ${}^7\mathrm{Li}$.

Ground state wave functions of the halo nuclei ${}^6$He and ${}^8$He have been determined by a genetic algorithm in the framework of the refined resonating group model. The genetic algorithm allows one to apply the underlying variational principle to very complex wave functions and to extract their most important structures in order to give a physical interpretation. The spectrum of the particle unstable isotopes ${}^{A+1\mathrm{}}$He${}_{N+1\mathrm{}}$ has been determined from the phase shifts of neutron scattering on the particle stable nuclei ${}^A$He${}_N.$ Stepwise going on, using the same $\mathrm{NN}$ potential in the refined resonating group method bound state and scattering calculation, yielded a consistent description of the nuclei ${}^{4,5,6,7,8}$He.

We review briefly the fundamental equations of a semimicroscopic core-particle coupling method that makes no reference to an intrinsic system of coordinates. We then demonstrate how an intrinsic system can be introduced in the strong coupling limit so as to yield a completely equivalent formulation. It is emphasized that the conventional core-particle coupling calculation introduces a further approximation that avoids what has hitherto been the most time-consuming feature of the full theory, and that this approximation can be introduced either in the intrinsic system, the usual case, or in the laboratory system, our preference. A new algorithm is described for the full theory that largely removes the difference in complexity between the two types of calculation. Comparison of the full and approximate theories for some representative cases provides a basis for the assessment of the accuracy of the traditional approach. We find that for well-deformed nuclei, e.g., ${}^{157}$Gd and ${}^{157}$Tb, the core-coupling method and the full theory give similar results.

The two-neutrino double beta decay of ${}^{92}$Mo to the ground state and excited states of ${}^{92}$Zr is analyzed using the shell-model approach and the quasiparticle random-phase approximation (QRPA). Two different valence spaces and three different Gamow-Teller operators are used in the shell-model analysis. The resulting double beta matrix elements and half-lives are compared with the corresponding QRPA results.

Carrying out particle-rotor model calculations, we have studied how stable the intrinsic structures of the $K^{\pi }{=1\mathrm{}}^{+},I=1\mathrm{}$ states of two unique-parity, high-$j$ quasiparticles are when the total spin is increased. We have found that the effect of the rotational perturbation is so large in high-$j$ 2$\mathrm{qp}$ configurations that no rotational bands develop on most of them. This result is at variance with the previously suggested configuration for a rotational band in ${}^{164}\mathrm{Dy}$.

In the present work, odd-odd ${}^{62,64,66}$Cu nuclei have been studied in the framework of the interacting boson-fermion-fermion model (IBFFM). Odd-odd Cu nuclei have been described with the parameters obtained from the IBM calculation for even Ni nuclei and the IBFM description of odd mass Cu and Ni nuclei. A simple delta interaction has been assumed between the odd neutron and the odd proton in the odd-odd nuclei. The calculated excitation energy values and the magnetic moments of odd Cu and Ni nuclei in the IBFM are compared to show the effectiveness of the parameters in explaining the low energy structure of these nuclei. Excitation energy spectra, magnetic moment and spectroscopic factors for the single-nucleon transfer reaction have been calculated for the odd-odd nuclei and are compared with the corresponding experimental values. The results seem to indicate the ability of the model to explain the low energy structure of odd-odd Cu nuclei.

Assuming that the wave function of the ${3/2}^{+}$ ground state of ${}^{223}$Ra is quadrupole-octupole deformed with ${\beta }_2,$ ${\beta }_4,$ ${\beta }_6,$ ${\beta }_3$, and ${\beta }_5$ having the optimum values of 0.129, 0.075, 0.004, 0.10, and 0.01, respectively, its amplitude in the wave functions of the $g_{9/2},$ $i_{11/2},$ $j_{15/2},$ $d_{5/2},$ $s_{1/2},$ and $g_{7/2}$ shell model states of ${}^{209}$Pb has been calculated. The systematics of the amplitudes as a function of the octupole deformation, ${\beta }_3$, provides physical insight into the failure to observe ${}^{14}$C radioactive decay to the $j_{15/2}$ state and the very different hindrance factors populating the $g_{9/2}$ and $i_{11/2}$ states in ${}^{209}$Pb.

We have determined the spectra of neutrons and protons following the decay of $\Lambda$ hypernuclei through the one- and two-nucleon-induced mechanisms. The momentum distributions of the primary nucleons are calculated and a Monte Carlo simulation is used to account for final state interactions. The shape of the proton spectrum is sensitive to the value of ${\Gamma }_n/{\Gamma }_p$ the ratio of neutron- to proton-induced decay, and the available experimental information favors larger values than those predicted by the one-pion-exchange model. From the spectra we calculate the number of neutrons ${(N}_n)$ and protons ${(N}_p)$ per $\Lambda$ decay and show how the measurement of these quantities, particularly $N_p,$ can lead to a determination of ${\Gamma }_n/{\Gamma }_p.$ We also show that the consideration of the two-nucleon-induced channel has a repercussion on the results, widening the band of allowed values of ${\Gamma }_n/{\Gamma }_p$ with respect to what is obtained neglecting this channel.

The magnetic moments of the $2^{+}$ to ${10}^{+}$ states of ${}^{138}$Ba and ${}^{136}$Xe have been estimated within the framework of cranked Hartree-Fock-Bogoliubov formalism. The variation of the $g$ factors of these states distinctly determines the neutron-proton alignment of the symmetry axes of the relevant nuclei. The theoretical results have been discussed with the available recent experimental results in this mass region.

We present a new method by which wave functions with simple structure are renormalized so as to contain more complicated structure. This method, called $H^n$-cooling method, is applied to the study of the quadrupole collective motion of ${}^{56}$Fe, ${}^{54}$Cr, ${}^{58}$Fe, and ${}^{56}$Cr. The shell-model wave functions of lowest-lying states of these nuclei are well treated by this method. By using the wave functions obtained via the $H^n$-cooling method, interacting boson model-2 parameters are derived from a realistic shell-model Hamiltonian and transition operators. The Majorana interaction becomes sizably repulsive, primarily as an effect of the renormalization. The bosonic $E2\mathrm{}$ effective charges are enhanced due to the renormalization, while a quenching occurs in the $M1\mathrm{}$ and $M3\mathrm{}$ parameters for proton bosons. It is shown that the $\chi$ parameters take similar values in the Hamiltonian and in the $E2\mathrm{}$ operator.

Neutron-rich $\mathrm{sdf}$ shell nuclei have been produced in deep-inelastic processes during collision of 230 MeV ${}^{37}$Cl ions on a thick ${}^{208}$Pb target. The in-beam as well as off-beam $\gamma$-$\gamma$ coincidence data yielded new spectroscopic information on some hard-to-access $N=18,19\mathrm{}$ isotones. A new 27 ns isomer at 5583 keV in ${}^{32}$Si has been located. A candidate for the negative parity state 4${}^{-}$ has been identified above the 200 ns isomer in ${}^{32}$Al.

We have measured the ratio of the yields for the metastable and ground states of ${}^{119}$Te produced in the fusion-evaporation reactions ${}^{110}$Pd${(}^{12}$C,3$n)$ and ${}^{115}$In${(}^7$Li,3$n)$ by off-line observation of delayed $\gamma$-ray emission. The absolute cross sections for the formation of the metastable ${(J}^{\pi }$ = 11/2${}^{-}$, $T_{1/2}$ = 4.68 d) and ground ${(J}^{\pi }$ = 1/2${}^{+}$, $T_{1/2}$ = 16.05 h) states were determined at energies close to the Coulomb barrier for both systems. We have deduced the average angular momentum from these isomer ratio measurements through statistical model calculations. The deduced mean angular momentum agrees quite well with those calculated by a simple fusion model. The expected constant value of the average total angular momentum at subbarrier energies was confirmed for the ${}^{12}$C+${}^{110}$Pd system. The predicted variation of the mean orbital angular momentum with the reduced mass of the entrance channel was also verified.

The problem of fragmentation of excited finite systems is explored in the frame of classical molecular dynamics experiments of two-dimensional Lennard-Jones drops. The main objective of this work is to get information about the relative value of the relevant characteristic time scales (CTS) for this kind of process. We investigate the CTS for fragment formation, the stabilization of the radial flux, and the internal “temperature.” It is found that the asymptotic fragments are realized early in phase space, when the system is still dense, by the time the radial flux attains its asymptotic value. It is also shown that the temperature of the system during the breakup is quite homogenous with respect to the expected profile if local thermal equilibration takes place. Special emphasis is put on the investigation of the time scale of stabilization of the statistical properties of the mass spectrum, which is related to the kind of information carried by the asymptotic fragments.

Recent experimental studies show a characteristic energy dependence of the different fragmentation modes in heavy-ion reactions at intermediate energies. In this work we study this dependence and find that, in multifragmentation, just like in low-energy fission, some modes of decay are more probable than the rest. We argue that these high-probability mass partitions are ultimately responsible for the observed energy dependence.

The explicit expressions for calculating the in-medium $N+N\to \Delta +\Delta$ and $\Delta +\Delta \to N+N$ cross section have been derived within the framework of the self-consistent relativistic Boltzmann-Uehling-Uhlenbeck approach in which the deltas and nucleons are treated on an equal footing. The obtained cross sections are consistent with the other integrands of the transport model. The theoretical prediction of the free double-$\Delta$ production cross section is in good agreement with the experimental data. All the medium effects on the double-$\Delta$ production and absorption cross section are studied systematically, and strong medium corrections are found. Our numerical results show that it would be important to take the $N+N\to \Delta +\Delta$ and $\Delta +\Delta \to N+N$ channel into account in the study of relativistic heavy-ion collisions at intermediate and high energies.

We present a detailed description of a recently proposed optical theorem formulation of nonresonant low-energy nuclear reactions between two charged nuclei. Based on the optical theorem formulation, we obtain an analytic formula for the reaction cross section σ(E) which exhibits explicitly the energy and charge dependences of σ(E). The formula may provide a physical understanding of the anomalous low-energy enhancement of σ(E) observed in sub-barrier heavy-ion fusions and also in light nuclei fusions relevant for primordial nucleosynthesis and stellar evolution. As examples of its application, the new formulation is used to analyze astrophysical S factors for ${}^7\mathrm{Li}(p,\alpha {)}^4\mathrm{He},$ ${}^6\mathrm{Li}(d,\alpha {)}^4\mathrm{He},$ and ${}^6\mathrm{Li}(p,\alpha {)}^3\mathrm{He}$ reactions.

The cross section for the removal of high-momentum protons from ${}^{16}\mathrm{O}$ is calculated for high missing energies. The admixture of high-momentum nucleons in the ${}^{16}\mathrm{O}$ ground state is obtained by calculating the single-hole spectral function directly in the finite nucleus with the inclusion of short-range and tensor correlations induced by a realistic meson-exchange interaction. The presence of high-momentum nucleons in the transition to final states in ${}^{15}\mathrm{N}$ at 60–100 MeV missing energy is converted to the coincidence cross section for the ${(e,e}^{\prime }p)$ reaction by including the coupling to the electromagnetic probe and the final state interactions of the outgoing proton in the same way as in the standard analysis of the experimental data. Detectable cross sections for the removal of a single proton at these high missing energies are obtained which are considerably larger at higher missing momentum than the corresponding cross sections for the $p$-wave quasihole transitions. Cross sections for these quasihole transitions are compared with the most recent experimental data available.

Radioisotope yields from 1.85-GeV proton interactions in a natural isotopic composition Mo target and those from 1.85- and 5.0-GeV protons in natural Te targets were measured at Lawrence Berkeley National Laboratory’s Bevatron. The radioisotope yields were determined by $\gamma$-counting the targets using 100-cm${}^3$ coaxial Ge detectors following the irradiations. Cross sections were determined for the production of 36 radioactive nuclides, ranging from $Z=35\mathrm{}$, $A=74\mathrm{}$ to $Z=43\mathrm{}$, $A=97\mathrm{}$, from the Mo target and for 43 radioactive nuclides, ranging from $Z=35\mathrm{}$, $A=75\mathrm{}$ to $Z=53\mathrm{}$, $A=130\mathrm{}$ from the Te targets. The average deviations of the experimental cross sections from those predicted by the semiempirical isotopic cross sections of Silberberg and Tsao were 53% for $p$+Mo at 1.85 GeV, 66% for $p$+Te at 1.85 GeV, and 35% for $p$+Te at 5.0 GeV. These deviations are higher than those found previously for medium and heavy targets and for elemental cross sections. The minimum production cross section of ${}^{91}$Nb, which may be of interest as a cosmic-ray chronometer, was found to be $18\pm 3$ mb for the $p$+Mo reaction.