Bremsstrahlung from tritium–rare-gas mixtures enclosed in low-permeability glass bulbs has been observed with a Si(Li) detector. The end point of the x-ray spectrum, 18 556(6) eV, implies a ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^3{}_{}{}^{}$He atomic-mass difference of 18 595(6) eV.

The half-life of tritium has been measured by monitoring the decay of the x-ray bremsstrahlung emitted by gaseous mixtures of ${\mathrm{H}}_2^3$ and Xe. The result, 12.31±0.03 yr, when combined with the end-point energy measured on the same sources, yields the product (${\mathrm{G}}_{\mathrm{A}}$/${\mathrm{G}}_{\mathrm{V}}^{\prime }$)〈σ〉=2.098±0.003, where 〈σ〉 is the Gamow-Teller matrix element. Combined with a recent precise calculation of the matrix element, this value suggests that the renormalization of the axial-vector interaction can be entirely accounted for by nuclear effects in the triton. The deduced value of ${\mathrm{G}}_{\mathrm{A}}$/${\mathrm{G}}_{\mathrm{V}}^{\prime }$ constrains the neutron lifetime to lie in the range of 897±3 s.

The threshold electrodisintegration of the deuteron was measured with good energy resolution to a maximum four-momentum transfer squared of 42 ${\mathrm{fm}}^{\mathrm{-}2}$. The data are compared with meson exchange calculations that show sensitivity to the choice of exchange-current form factor, the nucleon electromagnetic form factors, and the nucleon-nucleon potential. While conventional theories can give a reasonable description of the data, comparison of the data with quark cluster calculations shows poor agreement.

Attempts to reconcile a 17-keV neutrino with constraints from astrophysics and double beta decay have led to model Majorana neutrino mass matrices with vanishing (or nearly vanishing) electron-electron components. A simple parametrization is presented of the higher-order mass effects on the intermediate-state propagator through which 0ν ββ decay can still occur. For light-mass eigenstates, the 0ν and 2ν rates are proportional, with the ratio depending on a weighted sum over mass eigenstates 〈${\mathit{m}}_{\nu }^3$${\mathrm{〉}}_{\mathit{L}\mathit{L}}^{\mathrm{Maj}}$. Thus, model 0ν ββ decay rates can be predicted with confidence.

We discuss the production of doubly strange ΛΛ hypernuclei in ${\mathrm{\Xi }}^{\mathrm{-}}$ atomic capture. The two-body ${\mathrm{\Xi }}^{\mathrm{-}}$${+}^6$Li${\to }_{\mathrm{\Lambda }\mathrm{\Lambda }}^6$He+n reaction is a relatively favorable case, with a yield of order 3%. For heavier p-shell targets, such as ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, the (1${\mathit{s}}_{\mathrm{\Lambda }}$${)}^2$ ground-state yields in the ${\mathrm{\Xi }}^{\mathrm{-}}$${+}^{\mathit{A}}$Z${\to }_{\mathrm{\Lambda }\mathrm{\Lambda }}^{\mathit{A}}$(Z-1)+n reaction are suppressed, and states of (1${\mathit{s}}_{\mathrm{\Lambda }}$1${\mathit{p}}_{\mathrm{\Lambda }}$) structure, coupled to an excited nuclear core, are preferentially populated.

Coincidence measurements of (p,n) reactions at 1.5 GeV/c in the Δ excitation region have been carried out for the first time. The location of the Δ peak in the neutron spectrum is found to be dependent on the coincident particles. The peak in coincidence with p${\mathrm{\pi }}^{+}$ is shifted to lower momenta compared to the free case, in contrast to the inclusive spectrum and the coincidence with other particles where it is shifted to higher momenta. The p${\mathrm{\pi }}^{+}$ invariant-mass distribution for C is significantly lower and broader than that for H. The coincidence data set stringent constraints on theoretical models introduced to interpret the peak shift in inclusive spectra.

Recent improvements to both the instrumentation and data-analysis techniques associated with the Manitoba II high-resolution mass spectrometer have led to greater precision and accuracy. The mass difference between ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$ and ${}_{}{}^{76}{}_{}{}^{}\mathrm{Se}$ has been redetermined to be 2038.56(32) keV. When this new Q value is used to reexamine recent spectra reported by groups searching for the characteristic sharp peak expected for neutrinoless double-beta decay, no evidence for the occurrence of such a decay is found. New upper limits can be derived for the electron-neutrino mass.

In order to investigate the coupling between collective flow of nucleons and pions in hot pion-dominated hadronic matter, we calculate the pion-nucleon drag coefficient in linearized transport theory. We find that the characteristic time for flow equalization is longer than the time scale of the expansion of a hardonic fireball created in high-energy collisions. The analysis of transverse-momentum data from p+p¯ collisions at √s =1.8 TeV reveals the same flow velocity for mesons and antinucleons. We argue that this may be evidence for the formation of a quark-gluon plasma in these collisions.

The detectability of collective transverse flow is discussed for CERN superproton synchrotron energies in Pb+Pb collisions. Calculations with a quark-gluon string model suggest there will be measurable flow in Pb+Pb reactions but not in S+S reactions at 160 GeV. Calculations of transverse flow with a fluid-dynamic model show a strong dependence on the equation of state and that the amount of flow is significantly larger than in the string model.

Multifragment disintegrations following ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$${+}^{197}$Au collisions at E/A=50 MeV have been studied with a multidetector system covering 88% of 4π in solid angle. The average number of intermediate-mass fragments (Z=3–20) increases strongly as a function of charged-particle multiplicity and reaches values larger than six for the most violent collisions. The results are compared to calculations with both dynamical and statistical models.

We study the effects of quark degrees of freedom on the nucleon-nucleon observables. The model we consider is built from the Paris potential for large and intermediate distances, supplemented by the quark cluster model for the core. The fit to the existing pp data set is not good. These results suggest that the good description of the NN interaction at short distances by quark models sometimes claimed in the literature could be questioned.

We have analyzed the pion-induced double-charge-exchange data for the direct population of the ground state of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ by the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$(${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$${)}^{11}$Li reaction. We find that the measured cross section determines the rms radius of the last two neutrons in ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ to be 5.$1_{\mathrm{-}0.9}^{+0.6\mathrm{}}$ fm, which corresponds to a total neutron rms radius for the nucleus of 3.${28}_{\mathrm{-}0.33}^{0.24}$ fm. We show that for large assumed neutron-halo radii the cross section decreases as the radius of the halo to the inverse sixth power and that a radius of 12 fm leads to a cross section which is 3 orders of magnitude smaller than that measured.

Target-fragment, shower-particle (meson), interacting-proton (36–400 MeV), and total multiplicities in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+Ag collisions from 5A MeV to 2×${10}^5$A MeV are studied. The target disintegration exhibits energy independence above 100A MeV even in the most central collisions. Above 5A GeV the energy dependences of the three different categories of particles are similar to those from proton-nucleus interactions. The absolute yield of target fragments is also the same while the yield of protons is twice as large and of shower particles 6–7 times larger in ${}_{}{}^{16}{}_{}{}^{}\mathrm{induced}$ central collisions as compared to p-nucleus reactions.

New precision angular distribution data for the D(γ,p)n reaction are presented for incident photon energies of 191 and 222 MeV. The difference of cross sections measured with orthogonal states of linear polarization is sensitive to the short-range behavior of the tensor interaction in models of the nuclear force. Comparisons with the Bonn and Paris potentials illustrate the sensitivity.

Recent data on central Si+Au collisions at 15A GeV are shown to imply an expectedly high degree of nuclear transparency. The paucity of observed midrapidlity protons and pions suggests that up to one half of the projectile nucleons may lose less than one unit of rapidity after traversing 5–10 fm of nuclear matter.

We have studied multifragment decays of Au projectiles after collisions with C, Al, and Cu targets at a bombarding energy of 600 MeV nucleon. We find that with increasing violence of the collision, measured via the multiplicity of light particles, the mean multiplicity of intermediate-mass fragments originating from the projectile first increases to a maximum 〈${\mathit{M}}_{\mathrm{IMF}}$〉≃3 and then decreases again. Calculations using the Boltzmann-Uehling-Uhlenbeck model suggest that the fragmentation is governed by the energy ${\mathit{E}}_{\mathrm{dep}}$ deposited into the projectile spectator and that 〈${\mathit{M}}_{\mathrm{IMF}}$〉 reaches its maximum around ${\mathit{E}}_{\mathrm{dep}}$≃8 MeV/nucleon.

A xenon time projection chamber with an active volume of 207 L has been built to study neutrinoless double β decay in ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$. Data were taken in the Gotthard Underground Laboratory, with 5 atm of xenon enriched to 62.5% in ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$. From 3380 h of data, no evidence has been found for the 0ν $0^{+}$→$0^{+}$ transition. Half-life limits of ${\mathit{T}}_{1/2}^{0\nu }$>2.5(4.9)×${10}^{23}$ yr in the mass-mechanism mode and ${\mathit{T}}_{1/2}^{0\nu }$>1.7(3.2)×${10}^{23}$ yr in the right-handed-current mode, at the 90(68)% C.L., were derived. An upper limit for the Majorana neutrino mass parameter was deduced.

Prescission charged-particle multiplicities, following fusion of ${}_{}{}^{164,167,170}{}_{}{}^{}\mathrm{Er}$${+}^{28}$Si, have been measured. The multiplicities at the lowest bombarding energies limit the statistical model level density parameters. More importantly, the α data restrict the time spent near equilibrium and suggest evaporation occurs predominantly from larger deformations.

The relative strength (ΔS=1)/[(ΔS=0)+(ΔS=1)] of isovector spin excitations, ${\mathit{P}}_{\mathrm{sf}}$, in the high-lying resonance region of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ was investigated with the ${(}^7$Li${,}^7$Be) reaction at ${\mathit{E}}_{\mathit{L}}$=26 MeV/nucleon and ${\mathrm{\theta }}_{\mathit{L}}$=0° by separately measuring the ${(}^7$Li${,}^7$${\mathrm{Be}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$) and ${(}^7$Li${,}^7$${\mathrm{Be}}_{0.43}$ MeV) reaction channels with the ${}_{}{}^7{}_{}{}^{}\gamma$ coincidence technique. The relative strength ${\mathit{P}}_{\mathrm{sf}}$ was derived up to an excitation energy of 18 MeV in ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ and found to have a constant value of 0.4–0.5 for the continuum irrespective of excitation energy and 0.5 for the isovector dipole resonance centered at ${\mathit{E}}_{\mathit{x}}$=7.6 MeV.

The mixed-symmetry $2^{+}$ state of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ is investigated by a large-scale shell-model calculation. We can reproduce the experimental energy levels by the Kuo-Brown interaction, as well as the E2 and M1 transition probabilities. The (e,e’) form factors are also reproduced by including the core-polarization effect. By inspecting the shell-model wave functions thus tested, it is found that the $2_2^{+}$ and $2_4^{+}$ states share a large fraction of the mixed-symmetry component.