The quadrupole moment of the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ (${\mathit{I}}^{\mathrm{\pi }}$=$2^{+}$, ${\mathit{T}}_{1/2}$=769 msec) nucleus was measured as ‖Q${(}^8$B)‖=68.3±2.1 mb by use of modified β-NMR. This value is twice as large as the prediction of the Cohen-Kurath shell model. It is found by subtracting the contribution of deeply bound neutrons that the protons in ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ carry more than 90% of the observed moment. The anomalous value is accounted for fairly well by the proton halo due to the loosely bound valence configuration. This is the first experimental evidence for the existence of a proton halo covering a neutron core.

Nuclear disks and bubbles formed in central heavy-ion collisions, as simulated by means of Boltzmann-like kinetic equations, break up into several fragments due to a new kind of Rayleigh-Taylor-like surface instability. We demonstrate that a sheet of liquid, stable in the limit of noninteracting surfaces, becomes unstable due to surface-surface interactions. The onset of this instability is determined analytically. The relevance of this instability to nuclear multifragmentation is discussed.

Nuclear transport theory predicts the formation of unstable bubbles and rings in the central collision between equal-mass heavy ions. This phenomenon occurs around a beam energy of E/A≊50 MeV/nucleon and is due to the compression of the nuclei in the early stage of the collision. As observable consequences, we predict a higher number of intermediate-mass fragments than expected from multifragmentation of a homogeneously filled sphere, and a different pattern of fragment Coulomb accelerations.

The nuclear-breakup and Coulomb-breakup contributions to the sequential breakup of 156-MeV ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ by ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ via the $3^{+}$ resonance state of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ at 2.186 MeV are investigated by three-body calculations based on the continuum-discretized coupled-channels method. The nuclear-breakup contribution is as important as the Coulomb-breakup one up to forward angles where the Coulomb breakup was believed to be dominant. The effects of multistep processes via various nonresonant continuum states due to the three-body dynamics are also found to be important.

The excitation function of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(α,γ${)}^{16}$O reaction and the angular distribution of its γ rays were measured at nine energies ranging from ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=1.37 to 2.98 MeV. These measurements allowed the separation of the E1 and E2 contributions and their extrapolation to the region of astrophysical interest. The analysis of the E1 cross sections with a three-level R-matrix method yields a prediction of $1_{\mathrm{-}1}^{+6\mathrm{}}$ keV b for the S factor at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=0.3 MeV. The contribution of E2 transitions at the same energy is 40±7 keV b from a cluster-model analysis of the present data.

We have performed quasiparticle-random-phase-approximation (QRPA) calculations of the νν transition matrix for ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$, ${}_{}{}^{82}{}_{}{}^{}\mathrm{Se}$, and ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$, using effective interactions derived from the Paris and the Bonn NN potentials. Unlike earlier QRPA calculations where the self-energy corrections to the single-particle spectra were suppressed, we have retained these corrections as given by our interactions. In this way our calculations are able to avoid the commonly encountered difficulty of QRPA instability near ${\mathit{g}}_{\mathrm{pp}}$=1. The ${\mathit{M}}^{2\nu }$ matrix elements of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$, ${}_{}{}^{82}{}_{}{}^{}\mathrm{Se}$, and ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$ given by our calculation, with no adjustable parameters, are in reasonably good agreement with recent direct counter experiments.

Lifetimes of states in two ΔI=1 bands in ${}_{}{}^{198}{}_{}{}^{}\mathrm{Pb}$ have been measured using the Doppler-shift attenuation method. The in-band reduced transition probabilities are ∼1–2 Weisskopf units assuming magnetic dipole transitions. The measured lifetimes in conjunction with the partial level scheme support an oblate collective interpretation for these structures.

A comprehensive study of odd-A rotational bands in normally deformed rare-earth nuclei indicates that a large number of seniority-one configurations (30% for odd-Z nuclei) at low spin have moments of inertia nearly identical to that of the seniority-zero configuration of the neighboring even-even nucleus with one less nucleon. It is difficult to reconcile these results with conventional models of nuclear pair correlation, which predict variations of about 15% in the moments of inertia of configurations differing by one unit in seniority.

Based on the systematics for hard photon production a scheme is suggested which relates the hard-photon multiplicity observed in intermediate energy heavy ion reactions to the impact parameter. The method is applied to data obtained in an exclusive experiment of the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{158}$Gd at 44 MeV/nucleon, demonstrating the usefulness of this new approach.

Angular correlation functions for the ${\mathrm{He}}^4$(${\mathrm{\pi }}^{\pm }$,${\mathrm{\pi }}^{\pm \prime }$t)p reaction at the incident energy ${\mathrm{T}}_{\mathrm{\pi }}$=180 MeV and at four pion scattering angles have been measured. The ${\mathrm{He}}^4$(${\mathrm{\pi }}^{\pm }$,${\mathrm{\pi }}^{\pm \prime }$t)p data complement previous ${\mathrm{He}}^4$(${\mathrm{\pi }}^{\pm }$,${\mathrm{\pi }}^{\pm \prime }$p)t results by greatly extending the available range of proton emission angles. We calculate angular correlation functions of the cross sections with three different quasifree knockout models, and we show that direct triton knockout is crucial to an understanding of the data. © The American Physical Society

Three decoupled (ΔI=2) rotational bands have been observed to rise out of irregular spherical excitations in ${}_{51}{}^{117}{}_{}{}^{}\mathrm{Sb}$ at moderate spin. These bands are interpreted as resulting from low-lying π${\mathit{g}}_{7/2}$, π${\mathrm{d}}_{5/2}$, and π${\mathit{h}}_{11/2}$ valence orbitals outside the Z=50 closed shell coupled to the deformed [(π${\mathit{g}}_{7/2}$${)}^2$⊗(π${\mathit{g}}_{9/2}$${)}^{\mathrm{-}2}$${]}^{116}$Sn core state at the N=66 midshell. The valence orbitals do not significantly influence either the spherical or the deformed core shape; the latter is regulated by the β at which the π${\mathit{g}}_{7/2}$ and the intruder π${\mathit{g}}_{9/2}$ levels cross. Two strongly coupled (ΔI=1) bands involving [(π${\mathit{g}}_{7/2}$${)}^2$⊗(π${\mathit{g}}_{9/2}$${)}^{\mathrm{-}1}$] were also observed.

The energy region from the π threshold up to the Roper resonance N(1440) has been investigated in inelastic α scattering on hydrogen using α particles from SATURNE with a beam momentum of 7 GeV/c. In addition to projectile excitation, excitation of the ${\mathit{P}}_{11}$(1440 MeV) resonance has been observed for the proton, indicating a strong monopole excitation. From this a value of the nucleon compressibility of 1.4±0.3 GeV is extracted.

From the measured yield of δ electrons with energies between 3 and 8 MeV, emitted in the heavy-ion reaction Pb+Pb at 12 MeV nucleon incident energy, a very fast deceleration of the nuclei in the approach phase is inferred which is much faster than predicted by the microscopic one-body dissipation model. Since the deceleration time is smaller than or comparable to the thermal equilibration time, the dissipation process is non-Markovian and therefore memory effects have to be included. This is performed on the basis of dissipative diabatic dynamics, which describes elastoplastic properties. The new diabatic one-body dissipation model reporduces the fast deceleration and the long nuclear contact time.

It is shown that identical rotational energy spacings in pairs of even-even nuclei do not set these nuclei qualitatively apart from others. Rather, they represent the terminus or limiting case of a continuous range of spacings whose behavior is controlled by the balance between residual p-n pairing interactions and whose phenomenology can be simply described.

We calculate the average helicity dependence of the low-energy neutron-nucleus cross section in terms of a phenomenological optical model. Comparison with recent measurements on ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ by the TRIPLE Collaboration shows that the effective parity-nonconserving interaction is two orders of magnitude larger than estimates based on standard meson-exchange models. The helicity dependence is predicted to oscillate with target mass due to shape resonances.

In experiments employing fast ion-guide-based on-line mass separation we have identified six new, rare nuclides of highly refractory elements produced in the fission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ by 20-MeV protons. The new isotopes ${}_{}{}^{105}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{107}{}_{}{}^{}\mathrm{Nb}$, ${}_{}{}^{109}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{110}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{113}{}_{}{}^{}\mathrm{Tc}$, and ${}_{}{}^{115}{}_{}{}^{}\mathrm{Ru}$ were identified through (β, ${\mathit{K}}_{\mathrm{\alpha }}$ x-ray) coincidences and β-delayed γ decay. The observed β half-lives range from 130 ms to approximately 1 s. All our recent β half-life data are compared with predictions of the deformed quasirandom-phase-approximation model. The main uncertainty is found to be the inaccuracy of the decay energy predictions.

The E802 Spectrometer at the Brookhaven Alternating Gradient Synchrotron has been used to measure the correlations in relative momentum between like-sign pions emitted in central Si+Al and Si+Au collisions at 14.6A GeV/c. Data are presented in terms of the correlation function for both identified ${\mathrm{\pi }}^{\mathrm{-}}$ and ${\mathrm{\pi }}^{+}$ pairs near the nucleon-nucleon center-of-mass rapidity. All parametrizations of the correlation function are consistent with a spherically symmetric source of rms radius ${\mathit{R}}_{\mathrm{rms}}$≊3.5±0.4 fm and lifetime τ∼2 fm/c.

Calculations are presented for the Gamow-Teller strength distribution in the ${\mathrm{\beta }}^{+}$ decay of ${}_{}{}^{37}{}_{}{}^{}\mathrm{Ca}$ and compared to results extracted from recent beta decay data and from (p,n) data on the analog nucleus ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$. The strength distribution is shown to be sensitive to the Hamiltonian, and comparison with experiment indicates a need for further improvement in the 1s0d shell Hamiltonian. It also indicates that the quenching of the Gamow-Teller operator in the upper part of the 1s0d shell is similar to that deduced from previous analyses.

The effects of nucleon-nucleon correlations and color transparency on the final-state interaction of the struck nucleon in electron-nucleus scattering at high-momentum transfer are discussed. The results of realistic microscopic calculations show that both the mechanisms lead to an enhancement of the nuclear transparency, and that the correlation effects are larger up to momenta ${\mathit{Q}}^2$∼4 (GeV/c${)}^2$.

Using a recently developed Boltzmann-Langevin treatment, we study cluster formation in unstable nuclear matter. The self-consistent propagation of the spontaneous fluctuations restores the predictive power of the one-body approach, even when such catastrophic phenomena are addressed.