We describe a technique whereby the freeze-out interaction volumes of nucleus-nucleus collisions are extracted from a cascade (plus coalescence) model, after comparison to measured abundances of light nuclei. We conclude that the interaction volume undergoes significant expansion before light nuclei are produced.

The complete spectrum of $\gamma$ rays following the decay of superdeformed (SD) states in ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$ has been extracted. The spectrum, which comprises a quasicontinuous component and sharp lines, reveals the decay mechanism and defines the excitation energies of the SD band. The decay of SD states results from the coupling between a cold, ordered SD system with a hot, chaotic one with normal deformation.

An excited superdeformed (SD) band in ${}_{}{}^{150}{}_{}{}^{}\mathrm{Gd}$ is associated with a two-particle-two-hole proton excitation and provides the first evidence for collective proton pair excitations in a SD nucleus. This band is seen to exhibit a discontinuity in the $\gamma$-ray transition energies (backbending), which is interpreted as a band crossing associated with the alignment of a pair of $N=6\mathrm{}$ protons. There is further evidence that this excited SD band decays into the yrast SD band.

In bombardments of ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ with ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ we discovered two new isotopes, ${}_{}{}^{265}{}_{}{}^{}106$ and ${}_{}{}^{266}{}_{}{}^{}106$, by establishing genetic links between their $\alpha$ decays and spontaneous fussion (SF) or $\alpha$ decays of the daughter nuclides. We measured $E_{\alpha }=8.63\mathrm{}\pm 0.05$ MeV for ${}_{}{}^{266}{}_{}{}^{}106$ and a half-life of 1.2 s for its daughter ${}_{}{}^{262}{}_{}{}^{}104$. For ${}_{}{}^{265}{}_{}{}^{}106$ we measured $E_{\alpha }=8.71\mathrm{} \mathrm{to} 8.91$ MeV. From these $\alpha$ energies we estimated $\alpha$ half-lives of 10-30 s for ${}_{}{}^{266}{}_{}{}^{}106$ and 2-30 s for ${}_{}{}^{265}{}_{}{}^{}106$. We estimated SF branches of 50% or less for both isotopes. The decay properties of ${}_{}{}^{266}{}_{}{}^{}106$ establish the existence of enhanced nuclear stability near the predicted deformed shells $N=162\mathrm{}$ and $Z=108\mathrm{}$.

Recent data on multifragmentation in central Au+Au collisions at beam energy 100 MeV/nucleon are analyzed within the statistical and molecular dynamics models. The data are consistent with statistical breakup of a thermalized source with radius of 14 fm, mass number around 250, and excitation energy about 7 meV/nucleon, in good agreement with molecular dynamics calculations. According to this model, fragment formation takes place within a time interval of 50 fm/c after the maximum compression. Intense preequilibrium emission of light particles and strong collective flow of fragments are predicted.

Measurements of superallowed $0^{+}$ → $0^{+}$ nuclear $\beta$ decays, corrected for radiative and charge-dependent effects, yield fundamental properties of the weak interaction. Model predictions of the necessary corrections exist, but they have never been tested directly by experiment. The present work reports, for the first time, observations of (or limits on) nonanalog $0^{+}$ → $0^{+}$ branches in ${}_{}{}^{38m}{}_{}{}^{}\mathrm{K}$, ${}_{}{}^{46}{}_{}{}^{}\mathrm{V}$, ${}_{}{}^{50}{}_{}{}^{}\mathrm{Mn}$, and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Co}$, and tests of the model predictions for isospin-mixing corrections. The resulting unitarity test of the top row of the Kobayashi-Maskawa matrix is 0.9983 ± 0.0015.

The leading terms of a power series expansion in μ=${\mathit{M}}_{\mathrm{\pi }}$/${\mathit{M}}_{\mathit{N}}$ for the threshold amplitude of double-pion photoproduction on a nucleon are obtained by the use of an effective chiral Lagrangian. Contributions due to the Δ(1232) resonance are included.

The ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\gamma ,pp)n$ reaction was investigated in the photon energy range 200-500 MeV using the spectrometer TAGX, which has a solid angle for protons of $\pi$ sr. Two types of photon absorption, one by two protons and the other by three nucleons, were observed by looking at the undetected neutron momentum distributions. The total cross section for photon absorption by two protons shows that this process is consistent with the $E2\mathrm{}$ transition.

The first measurement of exclusive photodisintegration of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ with polarized photons is reported. Cross sections and asymmetries for ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\overrightarrow{\gamma },pn)p$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\overrightarrow{\gamma },pp)n$ at $235\le E_{\gamma }\le 305$ MeV are compared to a theoretical calculation which includes one-, two-, and three-nucleon photon, absorption. Two-nucleon absorption dominates the $\mathrm{pn}$ data, but is suppressed in the $\mathrm{pp}$ data. The $\mathrm{pp}$ data require the inclusion of three-nucleon absorption to describe the cross section and beam asymmetry over all momenta.

Lifetime measurements of the $3_1^{-}$, $5_1^{-}$, and $1_1^{-}$ states in ${}_{}{}^{144}{}_{}{}^{}\mathrm{Nd}$ show that the absolute $E2\mathrm{}$ and $E3\mathrm{}$ transition rates from the $5_1^{-}$ and $1_1^{-}$ states are consistent with their structure being formed by the coupling of the lowest quadrupole ($2_1^{+}$) and octupole ($3_1^{-}$) excitations. A level at 2205 keV has been identified as having $J^{\pi }=4^{-}$ and may be another member of this quadrupole-octupole coupled quintuplet. The energy spacing of the quintuplet can be explained by anharmonicities in the quadrupole-octupole interaction and the influence of the ${\nu }^2(2\mathrm{}{f}_{\frac{7}{2}},1\mathrm{}{i}_{\frac{13}{2}})$ configuration.

For temperatures above $T_c$ (where the nuclear equilibrium shape is spherical at rotational frequency $\omega =0\mathrm{}$), a small rotation can generate a prolate equilibrium shape "rotating" around its symmetry axis. This prolate spheroid is caused by a quantum shell effect which exists at positive $\omega$, but not at $\omega =0\mathrm{}$. For $T=1.5\mathrm{}$ MeV ($T_c$), ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}$ is prolate for all positive spins up to $60\hslash$.

The time independent mean field method for scattering defines biorthonormal sets of single-particle wave functions and corresponding creation and annihilation operators. Two-particle–two-hole (2p-2h) correlations can be introduced through a generalized random phase approximation; 1p-1h contributions vanish (Brillouin theorem). While the genreal variational method for scattering by Giraud and Nagarajan solves inhomogeneous Euler equations by inversion of the standard, Hermitean Hamiltonian, the present approach diagonalizes a non-Hermitean Hamiltonian, which carries the information about entrance and exit channels.

The efficiencies of solar neutrino detectors are often based in part on weak interaction strengths determined by (p,n) and other charge exchange reactions. Although the (p,n) determinations are surprisingly good, it is shown that they may be inaccurate for important Gamow-Teller transitions whose strengths are a small fraction of the sum rule limit. This emphasizes the importance of direct calibration with ν sources for detectors such as ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$ and ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ where direct β-decay information cannot be obtained. It may also bear on recent attempts to compare charge exchange and beta decay in the mass-37 system.

Intensity correlations between hard photons produced in heavy ion collisions have been measured for ${\mathit{E}}_{\gamma }$≥25 MeV in the reaction ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$${+}^{\mathrm{nat}}$Ni at 60A Mev bombarding energy. The observed correlation pattern is interpreted in terms of intensity interference. A correlation length of ${\mathit{C}}_{\mathrm{\sigma }}$=16±4 MeV is found and the deduced photon source extent is discussed.

We propose a theory of sequential charge exchange that describes, for the first time, the general features of the excitation function and the angular distributions of charge exchange on a ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ target to the isobaric and double isobaric analog states for pion kinetic energies up to 80 MeV. Our theory consists of conventional coupled-channel scattering through important low-lying states. We conclude that exotic contributions to the double charge exchange process must make a relatively small contribution (less than a factor of 2), effectively ruling out a prominent role for dibaryon resonances recently suggested as an explanation for the data.

Gamow-Teller strengths for selected nuclei in the iron region (A∼56) have been investigated via shell-model Monte Carlo calculations with realistic interactions in the complete ${\mathit{f}}_{\mathit{p}}$ basis. Results for all cases show significant quenching relative to single-particle estimates, in quantitative agreement with (n,p) data. The T=0 residual interaction and the ${\mathit{f}}_{7/2}$-${\mathit{f}}_{5/2}$ spin-orbit splitting are shown to play major roles in the quenching mechanism. Calculated B(E2,$2_1^{+}$→$0_1^{+}$) values are in fair agreement with experiment using effective charges of ${\mathit{e}}_{\mathit{p}}$=1.1e and ${\mathit{e}}_{\mathit{n}}$=0.1e.

An effective mean field approximations for finite systems at finite temperature which incorporates a multiplicity in the intrinsic partition function is derived in the context of the static path approximation. The approach exhibits a smooth behavior without sharp transitions. Moreover, the saddle point approximation around the new mean field is seen to provide an accurate estimate of the static path integral at all temperatures. Results are shown for a heavy nucleus with a quadratic interaction.

Fusion excitation functions for ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ have been measured to high precision. The extracted fusion barrier distributions show a double-peaked structure which is interpreted in terms of coupling to inelastic excitations of the target. The effect of the neutron stripping channel is evident in the reaction with ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$. These barrier distributions show clearly the signatures of specific inelastic and transfer channels.

If density isomers exist they can be detected by measuring the excitation function of subthreshold kaon production. When the system reaches the density where the density isomer has influence on the equation of state (which depends on the beam energy and on the optical potential), we observe a jump in the cross section of the kaons whereas other observables change little. Above threshold Λ¯’s or p¯’s may be used to continue the search. This is the result of microscopic Boltzman-Uehling-Uhlenbeck calculations.

We study the conditions under which the nucleons inside a deformed nucleus can undergo chaotic motion. To do this we perform self-consistent calculations in semiclassical approximation utilizing a multipole-multipole interaction of the Bohr-Mottelson type for quadrupole and octupole deformations. For the case of harmonic and nonharmonic static potentials, we find that both multipole deformations lead to regular motion of the collective coordinate, the multipole moment of deformation. However, despite this regular collective motion, we observe chaotic single-particle dynamics.