Wiescher, Görres, and Thielemann suggested that a "missing" $J^{\pi }=3^{+}$ level in ${}_{}{}^{18}{}_{}{}^{}\mathrm{Ne}$ should occur at $E_x\approx 4.33$ MeV, only ≈410 keV above the ${}_{}{}^{17}{}_{}{}^{}\mathrm{F}$+$p$ threshold. They noted that this level would provide an $s$-wave resonance in the ${}_{}{}^{17}{}_{}{}^{}\mathrm{F}(p, \gamma )$ reaction, greatly increasing its thermonuclear reaction rate. This, in turn, would have a pronounced effect on the production of ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ in explosive stellar environments. We have searched for this level using the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({}_{}{}^3{}_{}{}^{}\mathrm{He}, n)$ reaction. High-resolution time-of-flight spectra show that the $3^{+}$ level occurs at $E_x=4.561\mathrm{}\pm 0.009$ MeV, ≈230 keV higher than suggested. The astrophysical consequences of this result are discussed.

Dilepton production is studied in heavy-ion collisions at bombarding energies from 60 to 400 MeV/nucleon. The dynamical evolution of the nucleus-nucleus collisions is described by a transport equation of the Vlasov-Uehling-Uhlenbeck type including explicitly pion and Δ(1232) degrees of freedom and considering free on-shell production processes. We calculate the contribution of proton-neutron bremsstrahlung, ${\mathrm{\pi }}^0$ and Δ Dalitz decay, and ${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$ annihilation. At 60 MeV/nucleon bombarding energy proton-neutron bremsstrahlung dominates while around 100 MeV/nucleon most of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ cross section arises from ${\mathrm{\pi }}^0$ decay. At 400 MeV/nucleon, however, the Δ Dalitz decay is the most important dilepton source for invariant masses M>140 MeV thus offfering the possibility to study in-medium properties of this resonance.

By studying light charged particles emitted in coincidence with projectile-like fragments, we probe heavy ion reaction mechanisms that result in the production of light particles in peripheral collisions. Triple coincidence α-α${\mathrm{-}}^{12}$C correlations in the reactions of 35 MeV/nucleon ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with Ni conclusively identify previously known sources of light particles. The fast, beam velocity component of α particles in coincidence with projectile-like fragments is associated with the breakup of the projectile. The correlations suggest that the origin of the intermediate velocity component of α particles is the target nucleus. Both of these components are characterized by α particles emitted during the early stages of the collision.

The double isovector giant-dipolar state has been observed in the (${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$) Δ${\mathit{T}}_{\mathit{z}}$=+2 and (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) Δ${\mathit{T}}_{\mathit{z}}$=-2 double-charge-exchange reactions on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$. The resonances observed in the (${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$) reaction are closely related via Coulomb energy and isospin symmetry to the resonances measured in the inverse (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) reaction on the same nuclei. The new observations provide strong support for the identification of the double giant-dipole state in nuclei. The differences between the self-conjugate and non-self-conjugate cases are outlined.

The process of direct two-proton decay of nuclei with Z=22–28 on the proton drip line is considered. On the basis of new 0${\mathit{d}}_{3/2}$-0${\mathit{f}}_{\mathit{f}/2\mathrm{}}$ shell-model mass extrapolations, ${}_{}{}^{39}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{42}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{45}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{49}{}_{}{}^{}\mathrm{Ni}$ are found to be bound to single-proton decay but unbound to two-proton decay. New estimates of the spectroscopic factors and lifetimes have been made. The decays of ${}_{}{}^{39}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{45}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ni}$ are found to be promising for further experimental investigation.

We propose a new, deterministic method of solution of the nuclear Boltzmann equation. In this ‘‘weighted particle method,’’ two-body collisions are treated by a master equation for an occupation probability of each numerical particle. We apply the method to the quadrupole motion of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. A comparison with usual stochastic methods is made. Advantages and disadvantages of the weighted particle method are discussed.

The enhancement of two-step processes is analyzed for cases where the intermediate states and final states are influenced by a residual interaction, which splits the intrinsic configurations without changing total strength.

Published phase shifts (in R-matrix and effective range parametrized forms) fitted to protons scattering from ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, for energies up to 23 MeV, have been inverted to give two alternative energy-dependent local potentials. One is l independent, the other has a substantial Majorana character; there are very strong reasons to prefer the latter as a potential model for proton scattering from ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The analysis has novel features: Energy ‘‘bites’’ are introduced as a tool for exploiting the extension of the iterative-perturbative inversion procedure to ‘‘mixed-case’’ inversion for spin-half projectiles. An analysis of R-matrix parametrized phase shifts for neutrons reveals equal n${\mathrm{-}}^4$He and p${\mathrm{-}}^4$He nuclear potentials.

We have analyzed recent data for pion elastic scattering on the three-nucleon system to extract the relative neutron-proton radii in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$. Using standard multiple-scattering analysis techniques we determine the difference between the odd radii with an uncertainty of ±0.007 fm and that between the even radii within ±0.010 fm from the existing data. Additional data and improvements in the scattering theory can be expected to lead to a more precise determination. To assess the significance of the extracted radius differences we compare them with radii determined from Faddeev calculations that include charge-symmetry-breaking forces.

Inclusive electrodisintegration of the deuteron with polarized beam and target is investigated in detail. The additional polarization form factors are derived and their decomposition into multipoles is given. The sensitivity of these form factors to the potential model, to subnuclear degrees of freedom, and to electromagnetic form factors is studied in different kinematical regions.

Specific patterns have been found in the relative phases of the amplitudes of various strong-interaction reactions like proton-proton, pion-nucleon, or pion-deuteron scattering. Here we investigate such patterns for the case of π-d elastic scattering. We show that these phase patterns result essentially from the dominance of the delta resonance.

I study a simple model ‘‘nucleon,’’ which can only absorb electric dipole radiation. This nucleon will scatter both electrically and magnetically, if its mass is of the same order of magnitude as its excitation energy. Therefore it has a static electric polarizability α as well as a susceptibility β, which are of similar size and of opposite sign. This contradicts naive expectations. The reasons for this unexpected behavior will be analyzed in some detail. Furthermore, numerical results are obtained within a constituent quark model. It turns out that the energy dependence of the electric polarizability and magnetic susceptibility is very weak for photon energies up to 100 MeV.

The free two-nucleon W matrices are studied for a number of two-nucleon channels, including coupled channels, and over a range of laboratory energies to 250 MeV. For realistic interactions these W matrices are shown to be simple, smooth, and real functions of (half-on-shell) momenta. The free two-nucleon t matrices are expanded in separable form by the W matrices and the (fully off-shell) remainder matrices left thereby should have a negligible effect in any (low-energy) few-body calculation.

To simulate the effects of the breakup channel on rearrangement amplitudes, the conventional coupled-reaction-channel (CRC) expansion is augmented by pseudoreaction channels. The construction of the projector for the extended CRC space is discussed, and transition-operator equations on this space are given. By solving the full and post-approximation forms of the CRC equations for a model three-particle problem, the crucial role played by the nonorthogonality terms is demonstrated.

The electron-capture and ${\mathrm{\beta }}^{+}$-decay branchings (EC/${\mathrm{\beta }}^{+}$) and delayed proton decays of A=142 isotopes with 61≤Z≤66 and A=140 isotopes with 63≤Z≤65 were investigated with the OASIS facility on-line at the Lawrence Berkeley Laboratory SuperHILAC. Electron capture and positron-decay emission probabilities have been determined for ${}_{}{}^{142}{}_{}{}^{}\mathrm{Pm}$ and ${}_{}{}^{142}{}_{}{}^{}\mathrm{Sm}$ decays, and extensive decay schemes have been constructed for ${}_{}{}^{142}{}_{}{}^{}\mathrm{Eu}_{}^{\mathit{g}}{}_{}{}^{}$(2.34±0.12 s), ${}_{}{}^{142}{}_{}{}^{}\mathrm{Gd}$(70.2±0.6 s), ${}_{}{}^{140}{}_{}{}^{}\mathrm{Eu}$(1.51±0.02 s), and ${}_{}{}^{140}{}_{}{}^{}\mathrm{Gd}$(15.8±0.4 s). Decay schemes for the new isotopes ${}_{}{}^{142}{}_{}{}^{}\mathrm{Tb}_{}^{\mathit{g}}{}_{}{}^{}$(597±17 ms), ${}_{}{}^{142}{}_{}{}^{}\mathrm{Tb}_{}^{\mathit{m}}{}_{}{}^{}$(303±17 ms), ${}_{}{}^{142}{}_{}{}^{}\mathrm{Dy}$(2.3±0.3 s), ${}_{}{}^{140}{}_{}{}^{}\mathrm{Eu}_{}^{\mathit{m}}{}_{}{}^{}$(125±2 ms), and ${}_{}{}^{140}{}_{}{}^{}\mathrm{Tb}$(2.4±0.2 s) are also presented. We have assigned γ rays to these isotopes on the basis of γγ and xγ coincidences, and from half-life determinations. Electron-capture and ${\mathrm{\beta }}^{+}$-decay branchings were measured for each decay, and β-delayed proton branchings were determined for ${}_{}{}^{142}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{142}{}_{}{}^{}\mathrm{Tb}$, and ${}_{}{}^{140}{}_{}{}^{}\mathrm{Tb}$ decays. ${\mathit{Q}}_{\mathrm{EC}}$ values, derived from the measured EC/${\mathrm{\beta }}^{+}$ branchings and the level schemes are compared with those from the Wapstra and Audi mass evaluation and the Liran and Zeldes mass calculation. The systematics of the N=77 isomer decays are discussed, and the intense $0^{+}$→$1^{+}$ and $1^{+}$→$0^{+}$ ground-state beta decays are compared with shell-model predictions for simple spin-flip transitions.

Thermal neutron capture gamma rays from germanium have been studied using an internal irradiation facility and a pair spectrometer. Energy and intensity of transitions in four germanium isotopes were determined and their level and separation energies inferred. The separation energies are ${\mathit{S}}_{\mathit{n}}$ ${(}^{71}$Ge)=7415.95±0.05 keV, ${\mathit{S}}_{\mathit{n}}$ ${(}^{73}$Ge)=6782.94±0.05 keV, ${\mathit{S}}_{\mathit{n}}$ ${(}^{74}$Ge)=10 196.31±0.07 keV, and ${\mathit{S}}_{\mathit{n}}$ ${(}^{75}$Ge)=6505.26±0.08 keV. The E1 reduced strength function, 〈${\mathrm{\Gamma }}_{\gamma \mathit{i}}$${\mathit{D}}^{\mathrm{-}1}$${\mathit{E}}_{\mathit{i}}^{\mathrm{-}3}$${\mathit{A}}^{\mathrm{-}2/3}$〉, of these germanium isotopes was found to be (1.8±0.5)×${10}^{\mathrm{-}9}$ ${\mathrm{MeV}}^{\mathrm{-}3}$, a value lower than the global average. The M1 strength function 〈${\mathrm{\Gamma }}_{\gamma \mathit{i}}$${\mathit{D}}^{\mathrm{-}1}$${\mathit{E}}_{\mathit{i}}^{\mathrm{-}3}$〉 of ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$ was estimated to be (20±9)×${10}^{\mathrm{-}9}$ ${\mathrm{MeV}}^{\mathrm{-}3}$ which agrees with the global average. The average B(E2)↓¯ of ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$ using the present thermal data and the previous resonance data from literature was found to be 18±10${\mathit{e}}^2$ ${\mathrm{fm}}^4$ MeV ${}_{}{}^{\mathrm{-}1}{}_{}{}^{}$ which agrees with the value predicted by the Axel-Brink hypothesis.

A search for deeply bound ${\mathrm{\pi }}^{\mathrm{-}}$ states in heavy nuclei was undertaken using the pion-transfer ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$(n,p) reaction at the TRIUMF CHARGEX facility. Monoenergetic 418-MeV neutrons from the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,n) reaction were used to induce (n,p) reactions on a segmented ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ target. The spectrum between 100- and 180-MeV excitation energy was measured with an energy resolution of 1.15 MeV (FWHM). In the region of 120–140 MeV, where the deeply bound pionic states were expected, the observed spectrum exhibited a smooth continuumlike behavior with a cross section of ≊0.8 mb/sr MeV. This resulted in an upper limit of 0.35 mb/sr for the production cross section of ${\mathrm{\pi }}^{\mathrm{-}}$ bound states in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. This cross section is substantially smaller than the estimate based on the plane-wave impulse approximation, showing the importance of the effect of distortion. The distortion effect is calculated and discussed.

Spectra of energetic protons above 35 MeV have been measured following negative muon capture from rest in Ca. The spectrum extends to the kinematic limit near 93 MeV, with a branching ratio of (2.3±0.3)×${10}^{\mathrm{-}4}$ per capture above 40 MeV. Nuclear cascade calculations of the proton and neutron spectra in this energy region are presented and are consistent with the measured proton spectrum when capture on correlated pp and np pairs in the nucleus is included. The ratio of capture on np to pp pairs is 6.7±1.6, which is consistent with results from pion capture.

Giant resonances were observed in (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) double charge exchange on ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ at excitation energies of 8.8, 14.2, and 27.9 MeV, respectively, where the giant dipoles built on the isobaric analog states are expected to appear. Partial angular distributions were measured for both ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and observed to have a dipole shape. The resonance on the T=1/2 targets has a single isospin value (T=3/2) and is the analog of the ${\mathit{T}}_{>}$ giant dipole state in the above nuclei. The results are in good agreement with photonuclear reactions and indicate a new general method for an accurate determination of the ${\mathit{T}}_{>}$=T+1 giant dipole state in T=1/2 nuclei.