The relation between the folding angle distributions observed in the decay of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ into four alphas and the final alpha-alpha interactions is discussed and inferred from model calculations. Likewise, the excitation energy dependence of the four-alpha decay channel probability is studied. A lack of alpha-alpha interactions is deduced from the analysis and the observed energy dependence is found to be characteristic of a statistical decay. This reveals the statistical nature of the disassembly and suggests a sequential breakup as the decay method.

The ${\mathit{K}}^{\mathrm{\pi }}$=$8^{\mathrm{-}}$ isomer at 1147.4 keV in ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$ was populated in a Coulomb excitation experiment with ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$ ions. The measured cross section for this isomer was 2.7${\pm }_{1.4}^{1.9}$, 4.3${\pm }_{2.0}^{3.4}$, and 7.5${\pm }_{3.2}^{6.1}$ mb for three beam energies below the Coulomb barrier, namely 560, 590, and 620 MeV. If one assumes that the projection of the total angular momentum on the symmetry axis, K, is only an approximate quantum number, the population of this isomer can be reproduced via direct E3 excitations of odd spin members of the isomeric band from the ground state band.

The distortion on the intermittency signal, due to detection efficiency and to the presence of preequilibrium emitted particles, is studied in a schematic model of nuclear multifragmentation. A clear and genuine intermittency signal is generated by means of a percolating system, which is assumed to be in a region around the critical one. Mixing of events is considered to simulate the experimental conditions. The efficiency is schematized by a simple function of the fragment size, and the presence of preequilibrium particles is simulated by an additional noncritical fragment source. No selection on the events is considered, and therefore all events are used to calculate the moments. It is found that, despite the absence of event selection, the intermittency signal is not too much sensitive to the distortion due to the apparatus efficiency, while the inclusion of preequilibrium particles in the moment calculation can substantially reduce the strength of the signal. Preequilibrium particles should therefore be carefully separated from the rest of the detected fragments, before the intermittency analysis on experimental charge or mass distributions is carried out.

Excited states in ${}_{}{}^{77}{}_{}{}^{}\mathrm{Br}$ were investigated via the reactions ${}_{}{}^{75}{}_{}{}^{}\mathrm{As}$(α,2n${)}^{77}$Br and ${}_{}{}^{73,74}{}_{}{}^{}\mathrm{Ge}$${(}^7$Li,xn${)}^{77}$Br at beam energies of 27 and 35 MeV, respectively. On the basis of coincidence and angular distribution data of the γ rays the known level sequences of positive and negative parity were extended to tentative spins of 25/2ħ, and a new decay sequence beginning at spin and parity of (17/$2^{\mathrm{-}}$) was found. This new sequence is discussed in terms of the 3-quasiparticle configuration (π${\mathit{g}}_{9/2}$⊗ν${\mathit{g}}_{9/2}$⊗ν (${\mathit{p}}_{1/2}$,${\mathit{p}}_{3/2}$,${\mathit{f}}_{5/2}$)). Moreover, the irregularity found in the moments of inertia at ħω≊0.4 MeV for the negative-parity band is attributed to a ${\mathit{g}}_{9/2}$ quasiproton alignment.

Several approximation methods are tested in the four-nucleon bound-state problem as a means to understand how the two-nucleon tensor force propagates through the underlying (2)+(2) and (3)+1 subsystem amplitudes to yield a final four-nucleon binding energy. The aim is to show how to include as much of the nucleon-nucleon tensor force as possible in the dominant S-state component of the four-nucleon wave function for the purpose of optimizing the starting point in the iterative solution of the full problem.

From experimental E2 matrix elements, the asymmetry shape parameter ${\mathrm{\delta }}_{\mathit{e}\mathit{f}\mathit{f}}$ (corresponding to Bohr’s model parameter γ) is derived for the ground states of some fifty even-even nuclei with 94≤A≤192 (42≤Z≤76) by the sum-rule method. For the nuclei studied, an overall correlation between asymmetry and quadrupole deformation emerges.

We generalize the Goldhaber momentum-dispersion formula to the case of a ‘‘two-fluid’’ nucleus, in which the nucleons of one fluid have a different mean square momentum from those of the other fluid. The model predicts that fragments originated from the core of neutron-rich nuclei have a transverse momentum width which is significantly larger than that of a weakly bound ‘‘halo’’ neutron, and that both are much smaller than the ∼100 MeV/c widths observed in the fragmentation of less exotic nuclei.

We study the contribution of meson-exchange currents (MEC) to axial charge transitions in the framework of quantum hadrodynamics II. We extend a previous work which considered the contributions of one-body processes and vacuum polarization corrections. Calculations in mean-field theory (the Walecka model) and in the relativistic Hartree approximation are presented. In each of these cases we show results using pseudovector and pseudoscalar πN coupling. We find that the MEC contribution to the process is always sizable (much more so when using pseudoscalar coupling), transition dependent, and very sensitive to the coupling at the ρπ vertex.

The half-life of the 1897.2-keV, $3_1^{\mathrm{-}}$ state in ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}$ has been measured as (67.8±4.3) ps using the recoil-distance technique following inelastic excitation by 105-MeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ ions. This is equivalent to a lifetime which is about 40% longer than those reported from two recent centroid-shift measurements. Our lifetime implies B(E3)↑=(0.180±0.018) ${\mathit{e}}^2$${\mathrm{b}}^3$, i.e., (47.1±4.7) W.u., which is the most enhanced one-phonon g.s.→$3_1^{\mathrm{-}}$ transition strength observed in nuclei. A recent quasiparticle random-phase approximation (QRPA) calculation reproduces our result. Serious doubts are raised about an earlier conclusion that the reduced octupole transition probabilities of ‘‘mirror’’ nuclei correspond to the harmonic low for small amplitude vibrations. The enhanced B(E1:$3_1^{\mathrm{-}}$→$2_1^{+}$)=(1.71±0.11) ${10}^{\mathrm{-}5}$ ${\mathit{e}}^2$b deduced from the present work is consistent with appreciable octupole deformation. The measured B(E3)↑ resolves problems in the interpretation of the isospin character of the E3 transition derived from inelastic scattering data.

Lifetimes of states in the regular ΔI=1 band in ${}_{}{}^{197}{}_{}{}^{}\mathrm{Pb}$ have been measured with the Doppler-shift attenuation method. Excited states in ${}_{}{}^{197}{}_{}{}^{}\mathrm{Pb}$ were populated using the ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$${(}^{48}$Ca, 5n) reaction at ${\mathit{E}}_{\mathit{b}}$=210 MeV. The target consisted of 1 mg/${\mathrm{cm}}^2$ ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ evaporated onto a 10 mg/${\mathrm{cm}}^2$ Au backing. Discernible lineshapes for γ rays in the energy range 300<${\mathit{E}}_{\gamma }$<500 keV in the regular band were observed in a spectroscopic study with the 20 Ge-detector array, HERA. Level lifetimes were obtained from a lineshape analysis. Averaged reduced transition strengths, B(M1)∼1.7 W.u. and B(E2)∼18 W.u., are deduced and these are compared with theoretical predictions for the suggested configuration of this band.

Transitions in the very neutron-deficient ${\mathrm{isotope}}^{186}$Pb have been identified in mass-gated, recoil-γ, and recoil-γ-γ coincidence data obtained with a fragment mass analyzer and Compton-suppressed Ge-detector array. The results of the present work confirm and extend a band of levels tentatively proposed in earlier work done elsewhere, and provide a definitive mass assignment of the observed transitions. The band observed in ${}_{}{}^{186}{}_{}{}^{}\mathrm{Pb}$ bears a very close resemblance to the yrast band in the isotone ${}_{}{}^{184}{}_{}{}^{}\mathrm{Hg}$, supporting the view that the ${}_{}{}^{186}{}_{}{}^{}\mathrm{Pb}$ band is built upon a prolate structure.

We investigated the emission of light fragments from the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ target induced by 3.65A GeV ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ projectiles. The events are classified according to the number of heavy fragments. Two mechanisms of the production of light fragments are observed.

The availability of a target of ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$ in its aligned four-quasiparticle, ${\mathit{J}}^{\mathrm{\pi }}$=${16}^{+}$ isomeric state, has allowed to measure the effect of blocking of the aligned-quasineutron orbitals in the (p,t) reaction. The experimental ratio of cross sections R=${\mathrm{\sigma }}_{(16\mathrm{}}^{+}$→${16}^{+}$)/${\mathrm{\sigma }}_{(0\mathrm{}}^{+}$→$0^{+}$) agrees with a predicted value deduced from the known (p,t) cross section on odd Hf isotopes.

A new proton emission line has been observed in the nucleus ${}_{}{}^{156}{}_{}{}^{}\mathrm{Ta}$ using the fusion reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${+}^{102}$Pd${\to }^{160}$${\mathrm{W}}^{\mathrm{*}}$, ${\mathit{E}}_{\mathit{x}}$≃61 MeV. The line has a proton energy ${\mathit{E}}_{\mathit{p}}$=1103±12 keV corresponding to a Q value ${\mathit{Q}}_{\mathit{p}}$=1110±12 keV, and a half-life of 320±80 ms. The proton line is assigned to a ∼3% decay branch from a high spin π${\mathit{h}}_{11/2}$ν${\mathit{f}}_{7/2}$ isomeric state on the basis of systematics. The subsequent implications for level ordering in this region beyond the proton drip line are discussed.

Fully-energy-damped yields from the ${}_{}{}^{16,17,18}{}_{}{}^{}\mathrm{O}$${+}^{10,11}$B and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^9$Be reactions at ${\mathit{E}}_{\mathrm{lab}}$<5 MeV/nucleon have been identified and attributed to the process of the heavy-ion fusion followed by compound-nucleus fission. The large cross sections observed for these yields while in excess of those expected based on the conventional rotating liquid drop model are nonetheless found to be consistent with calculations using fission barrier energies more appropriate for light systems. An alternative explanation of the observed yields, based on the formation of a dinucleus orbiting complex, fails to account for the experimental results. This work offers the most compelling evidence yet obtained of the occurrence of fission process in light, s-d shell nuclei.

We discuss and interpret recently reported systematics of nuclide-to-nuclide variations in observed level spacings ${\mathit{E}}_{\gamma }$($4_1^{+}$→$2_1^{+}$) of even-even nuclei with 66≤Z≤76. We show that the reported empirical systematics can be explained theoretically by using Migdal’s 1959 formula for nuclear moments of inertia.

The ratio of unnatural to natural parity exchange in quasifree excitation of nuclei is calculated in the eikonal scattering limit. Calculations with and without random phase approximation (RPA) correlations in the nuclear response function are compared with the ratio deduced from a recent (p→,n→) experiment at LAMPF at 495 MeV bombarding energy and 1.7 ${\mathrm{fm}}^{\mathrm{-}1}$ momentum transfer. At small energy transfers the cross section is well described both with and without correlations. In this region, the RPA calculation predicts a strong enhancement of the spin-longitudinal reaction channel which reflects itself in an enhanced ratio of unnatural to natural parity exchange. The spin-transfer data from LAMPF provide no support for the hypothesis of correlations in the spin-longitudinal channel as implied by the RPA calculations.

We calculate positions of one- and two-particle, proton and neutron drip lines within the Hartree-Fock-Bogoliubov theory using Skyrme interaction. We also determine an approximate r-process path defined as a line where the neutron binding energy is equal to 2 MeV. A weakening of the nuclear shell structure at drip lines is found and interpreted as resulting from a coupling with continuum states.