We report the most sensitive direct upper limit set on the mass ${\mathit{m}}_{\nu }$ of the electron antineutrino. Our measurements of the shape of the β decay spectrum of free molecular tritium yield, under the assumption of no new physics other than that of mass, a central value for ${\mathit{m}}_{\nu }^2$ of -147±68±41 ${\mathrm{eV}}^2$, which corresponds to an upper limit of 9.3 eV (95% confidence level) on ${\mathit{m}}_{\nu }$. The result is in clear disagreement with a reported value of 26(5) eV.

Nucleon self-energies in nuclear matter are studied by analyzing the correlator of nucleon interpolating fields using QCD sum-rule methods. Large Lorentz scalar and vector self-energies arise naturally, and are comparable to the optical potentials of Dirac phenomenology. The key phenomenological inputs are the baryon density and the value of the nucleon σ term.

We present an analysis of the phenomena occurring whenever a level crossing is encountered. Besides Landau-Zener transitions and the quantum nonintegrable phase, fractionalization of quantum numbers and chaotic behavior emerge as intrinsically intertwined phenomena.

The cross section for the astrophysically important ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$(p,γ${)}^{14}$O reaction has been measured directly with an intense (3×${10}^8$ particles/s) and pure (>99%) 8.2-MeV ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ radioactive ion beam. The average value, for the 5.8–8.2-MeV ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ energy range, is 106(30) μb. The partial γ width of the resonance which occurs in this reaction at a center-of-mass energy of 0.545 MeV has been deduced to be 3.8(1.2) eV. It is compared with theoretical predictions and indirect determinations.

We report the first on-line measurements of quadrupole-interaction-resolved nuclear magnetic resonance on oriented nuclei. The 10-min ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ activity was obtained as daughter after cold implantation of mass-separated ${}_{}{}^{186}{}_{}{}^{}\mathrm{Hg}$ into a hcp Co single crystal at the NICOLE facility at ISOLDE-3 (CERN). The quadrupole interaction of ${}_{}{}^{186}{}_{}{}^{}\mathit{Co}$(hcp) was fully resolved, and the spectroscopic quadrupole moment of ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ was determined to be Q=+3.12(20) b. This implies ${\mathrm{\beta }}_2$=+0.246(16), proving the large prolate deformation of the ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ ground state.

The chaotic properties of the interacting-boson model of nuclei are studied both classically and quantum mechanically. Classical phase diagrams are constructed in the general parameter space of the Hamiltonian known as Casten’s triangle. They lead to a discovery of a nearly regular region which is probably related to an unknown approximate symmetry. Analysis of the quantum fluctuations of the spectrum and of the electromagnetic B(E2) intensities confirms the classical results. The phase diagrams may be useful in identifying ‘‘chaotic’’ nuclei within the nuclear periodic table.

Multifragment events for intermediate-mass fragments (3≤Z≤12) with multiplicity up to four have been observed in the reaction of 0.90 and 3.6 GeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ ions with ${}_{}{}^{\mathrm{natAg}}{}_{}{}^{}$ nuclei. Fragment energy spectra and angular distributions are found to be dependent on event multiplicity. The data suggest significant modification of the Coulomb field of the emitting source.

A search for neutrinos of mass 10–40 keV has been made by studying the internal-bremsstrahlung spectrum of ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$. We find evidence for a 17.2-keV neutrino with a mixing ratio of 1.6%.

Parity-nonconserving longitudinal analyzing powers were measured for 23 p-wave neutron resonances in ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$. Seven resonances show effects of greater than 2σ statistical significance (95% confidence)—the largest sample yet measured in a single nucleus. All seven analyzing powers have positive sign. Strong sign correlations are not a feature of the conventional statistical model of parity mixing between compound nuclear states. The results suggest that the mechanism of parity violation in resonance reactions is more complicated than previously assumed.

In one of the first measurements of its type, the nuclear response function ${\mathit{R}}_{\mathit{L}\mathit{T}}$ has been determined in the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(e,e’p${)}^{15}$N reaction in quasielastic kinematics for the ground state (1/$2^{\mathrm{-}}$) and the first excited state (6.32 MeV, 3/$2^{\mathrm{-}}$). Extracted momentum distributions for these two states exhibit asymmetric behavior. Spectroscopic factors show significant depletion of strength, consistent with previous results. ${\mathit{R}}_{\mathit{L}\mathit{T}}$ agrees better with relativistic distorted-wave impulse-approximation calculations in magnitude than does the total cross section.

Exclusive p-p correlations from the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${+}^{58}$Ni reaction at 850 MeV incident energy have been measured. The enhancement in the p-p correlation function observed for small values of Δp with a gate on ${\mathit{v}}_{\mathrm{rel}}$ is satisfactorily explained by stochastic proton emission followed by the p-p final-state interaction. A strong dependence of the p-p correlation function on the relative angle between the two-proton c.m. and the fragment velocities has been found. Also a dependence of the p-p correlation function on the Δp orientation with respect to the plane defined by the two-proton c.m. and the fragment velocities has been observed. This latter behavior has been attributed to angular momentum effects.

The ${\mathit{K}}^{\mathrm{\pi }}$=35/$2^{\mathrm{-}}$, five-quasiparticle isomer in ${}_{}{}^{179}{}_{}{}^{}\mathrm{W}$ is shown to decay into the region of a backbend in the 7/$2^{\mathrm{-}}$[514] band, allowing for the first time the identification of a full set of aligned-band states. Destructive interference results from level mixing in the band-crossing region. The deduced γ-ray branching ratios are used to establish the mixing matrix elements and to show that the aligned band has a high value of the K quantum number. The properties of well-defined alignment and yet also high K provide the first clear example of a Fermi-aligned s band. The anomalous decay of the isomer itself is now explained.

We show how to calculate the root-mean-square parity-violating matrix element M for a heavy nucleons of valence nucleon number ${\mathit{A}}_{\mathit{v}}$ in terms of a standard parity-violating interaction ${\mathit{V}}^{\mathrm{PV}}$. For large values of ${\mathit{A}}_{\mathit{v}}$, we find a scaling law for M in terms of ${\mathit{A}}_{\mathit{v}}$ and the number of core nucleus. We compare our results to a recent measurement of M in ${}_{}{}^{239}{}_{}{}^{}\mathrm{U}$, obtaining results that bracket the data for three previously determined parameter sets of ${\mathit{V}}^{\mathrm{PV}}$.

Exact numerical calculations with Lagrange constraints are used to determine the lowest terms in an expansion for the two-Skyrmion interaction. The nucleon-nucleon potential which results after semiclassical quantization compares better with the phenomenological Paris potential than do previous calculations in the Skyrme model which used the product approximation. In particular, the present calculations show a sizable medium-range attraction in the central channel, a result that is not found with the product approximation.

The tensor polarization ${\mathit{t}}_{20}$ of the recoil deuteron in elastic e-d scattering has been measured for three values of four-momentum transfer, q=3.78, 4.22, and 4.62 ${\mathrm{fm}}^{\mathrm{-}1}$. The data have been used to locate the first node in the charge monopole form factor of the deuteron at q=4.39±0.16 ${\mathrm{fm}}^{\mathrm{-}1}$. The results for ${\mathit{t}}_{20}$ are in reasonable agreement with expectations based on the nucleon-meson description of nuclear dynamics.

Entropy generation during an ultrarelativistic nuclear collision is discussed. It is shown that the maximum entropy densities attained are limited by the time during which the collision takes place. This provides a strong upper limit on the maximum entropy density attained in a collision of given multiplicity density.

Two-fragment (Be-Be, B-B, and C-C) correlation functions were measured at small relative momenta for noncompound fragment emission in ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$${+}^{197}$Au collisions at E/A=35 MeV. Interpretation of the experimental correlation functions in terms of final-state Coulomb-interaction models indicate average fragment-emission times of about 100–200 fm/c.

The cross section for the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’d${)}^2$H reaction has been measured as a function of the four-momentum transfer q at a missing momentum of 125 MeV/c. The data show that this reaction cannot be described as quasielastic knockout of a deuteron. In a microscopic description of the (e,e’d) cross section, assuming a direct knockout mechanism, the q dependence reflects the p-n relative wave function in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. However, even a calculation in this framework using a relativistic ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ wave function does not describe the data, indicating that other reaction mechanisms play a non-negligible role.

The energy distribution of protons from many reaction channels were studied following the fusion of ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at 110 MeV. Channel-dependent and angular-momentum-dependent effects were clear, but no evidence was found for structural effects within any final nucleus, contrary to recent claims.

The QCD sum-rule approach for a nuclear medium is developed. The medium dependence of the neutron-proton mass difference calculated from this approach gives effects in nuclei which have direct relevance for the resolution of the Okamoto-Nolen-Schiffer anomaly.