The absolute differential cross section for the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,p)n reaction has been measured using a large solid angle detector, with a tagged photon beam of mean energy 67 MeV. The data have been compared with nine different theoretical calculations of the cross section, which account for the data to varying degrees. Best agreement is obtained for models utilizing the nonrelativistic impulse approximation with a realistic nuclear potential, meson-exchange currents, and relativistic corrections.

We have developed a polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ target for polarized electron scattering measurements. The target has a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ density of 1.1×${10}^{20}$ nuclei ${\mathrm{cm}}^{\mathrm{-}3}$, a total length of 7.5 cm and thin glass windows of 120–180 μm thickness. ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ polarization as large as 40% was produced, limited only by the available laser power. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ polarization was maintained during bombardment with up to 22 μA of 578 MeV electrons. A measurement of elastic scattering of polarized electrons from polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ confirmed that the nuclei in the electron beam had the expected polarization. The polarization is produced by spin exchange with laser optically pumped Rb vapor, and the target design incorporates two separated volumes, one for optical pumping and the other for the electron bombardment. Extensions of this design are practical for fixed target electron scattering from polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ planned for SLAC and CEBAF.

A study of the strangeness production process p¯p→Λ¯Λ at threshold and intermediate energies has been performed doing a full coupled-channel (p¯p,Λ¯Λ) calculation. The elastic part of the p¯p and Λ¯Λ interactions has been derived from a one-boson-exchange version of the Bonn NN potential and a corresponding extension to the hyperon-nucleon case whereas the annihilation part is taken into account by introducing suitable optical potentials. The transition interaction between p¯p and Λ¯Λ is based on K- and ${\mathit{K}}^{\mathrm{*}}$-meson exchange. A reasonably good description of empirical cross sections as well as polarization data is achieved. It is demonstrated that the results are quite sensitive even to short-range modifications of the channel interactions. We also compare our model with other approaches and suggest a new experiment which would be able to check the very different predictions of the meson-exchange and constituent quark model, respectively.

The nonmesonic weak decay of ${}_{\mathrm{\Lambda }}{}^3{}_{}{}^{}\mathrm{H}$ is evaluated microscopically in the pion exchange model. The correlated three-body wave function of the hypertriton is approximated by a bound Λ-deuteron system obtained by averaging the YN interaction over the deuteron wave function. The relevant matrix elements are calculated in momentum space. The resulting decay rate is 4.9% of the free Λ decay rate.

We present a systematic investigation of the effect on a one-boson-exchange model of the NN and NN¯ systems of using either a small pion-nucleon coupling constant or a soft pion-nucleon form factor. Depending on the choice of low-energy pp data either of these changes can improve the overall fit. This conclusion is independent of whether or not retardation is included in the potential model. When the same models are applied to the NN¯ system we find little to cause us to prefer any one model over the others.

A three-dimensional relativistic equation with real time variables is derived from the Bethe-Salpeter equation. The kernel is uniquely determined by the Bethe-Salpeter kernel through an infinite series. The one-time kernel in the momentum representation is represented by a superposition of Feynman amplitudes with the particle 1 or the antiparticle 2 being on the mass shell. The numerical analysis shows that the one-time equation is equivalent to the Gross equation in the N-N scattering case.

The asymptotic form of the three-body scattering wave function in configuration space is investigated. The value of the distance for which the asymptotic form is an accurate approximation to the scattering wave function is studied in detail. It is shown that previous estimates of the value for this distance were too large. Using model equations that reproduce the essential features of the scattered wave function we investigate the propagation out of two sources with different spatial extents. One source is localized and corresponds to the Born approximation for nucleon-deuteron scattering; the other has a large spatial extent corresponding to the breakup behavior in the wave function itself. These numerical examples provide new estimates for the distance at which the asymptotic form for breakup is an accurate approximation to the scattered wave function.

A method for an unambiguous determination of deuteron asymptotic observables due to one-pion exchange is presented. The sensitivity of results to the pion-nucleon coupling constant is discussed.

The contribution of nonpionic dynamics to deuteron asymptotic observables is investigated. It is shown that effects due to ρ and ω exchanges are negligible.

A high-resolution (α,α’) experiment has been performed in order to confirm the existence of the low-energy octupole resonance (LEOR) in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. Until now there was a puzzling discrepancy; an (α,α’) experiment denied the existence, while a (p,p’) measurement affirmed it. The present (α,α’) reaction with an improved resolution of 27 keV has identified clustering L=3 levels in the ‘‘LEOR region’’ in agreement with the former (p,p’) measurement. The observed strength, however, is weaker than the (p,p’) results, suggesting the coexistence of the isovector strength.

The ${}_{}{}^{70,72}{}_{}{}^{}\mathrm{Ge}$(n,p${)}^{70,72}$Ga reactions have been measured at a beam energy of 200 MeV in order to study the behavior of Gamow-Teller (GT) strength near the N=40 subshell closure. The GT quenching factor extracted for ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$ is consistent with results for ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$ and with calculations done on the quasiparticle random-phase-approximation model if they are renormalized by a factor of about 0.6. The quasiparticle random-phase approximation predicts a drastic reduction in concentrated GT strength from ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$ to ${}_{}{}^{72}{}_{}{}^{}\mathrm{Ge}$ which is also seen in the data. These results are relevant to models of supernovae.

Discrete superdeformed bands in ${}_{}{}^{147,148}{}_{}{}^{}\mathrm{Gd}$ have been populated with asymmetric and symmetric fusion-evaporation reactions. The yields of the superdeformed bands compared with the total yield of the channel exhibit a large increase for symmetric reactions. We suggest an explanation for this effect in terms of the competition between neutron emission and fission at the early stage of the deexcitation process of the composite system.

Measurements of the linear polarization of resonantly scattered photons have been used for model independent parity assignments in nuclear resonance fluorescence experiments. The novel result of the present study was the first observation of enhanced electric dipole excitations in the deformed nuclei ${}_{}{}^{150}{}_{}{}^{}\mathrm{Nd}$ and ${}_{}{}^{162}{}_{}{}^{}\mathrm{Dy}$ at excitation energies of 2.414 and 2.520 MeV, respectively. The transition energies and the enhanced B(E1)↑ strengths of 3 and 5×${10}^{\mathrm{-}3}$ ${\mathit{e}}^2$ ${\mathrm{fm}}^2$ support the interpretation in terms of the predicted new type of collective electric dipole excitations in deformed nuclei due to reflection asymmetric shapes like octupole deformations and/or cluster configurations.

Six electric monopole (E0) transitions have been observed at low energy in ${}_{}{}^{185}{}_{}{}^{}\mathrm{Pt}$: These transitions have no observed γ rays. The observation of pure E0 transitions and of such a large number of E0 transitions in an odd-mass nucleus is unprecedented. The phenomenon is consistent with the mixing of shape isomeric configurations.

The unusual case in nuclear orbital electron capture whereby either a neutrino in a weak interaction eigenstate or in a mass eigenstate is emitted by the same nucleus is examined. The case of the low-energy Q value nuclear electron capture decays is considered where, for at least one electronic shell, the emission of a weak eigenstate neutrino having an admixture of a second mass eigenstate neutrino (with mass in the keV/${\mathrm{c}}^2$ range) is energetically prohibited. This feature, in particular, opens the possibility for a new approach to searching for massive neutrino admixtures using relative electron capture rates. Five candidates are specifically identified, of which one, ${}_{}{}^{157}{}_{}{}^{}\mathrm{Tb}$, is conceivably of immediate interest to the 17 keV/${\mathrm{c}}^2$ neutrino mass question. Finally experimental prospects and limitations are described.

According to the kinematic analysis two sets of laboratory angle pairs, coplanar and noncoplanar, were selected and the coincidence spectra of two protons outgoing from ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(d${,}^2$p)2n reaction induced by 15.7 MeV deuteron were measured. The resonant spectrum of the diproton has been obtained. The peak, mean, and width of the spectrum are 0.43±0.09 MeV, 0.45±0.05 MeV, and 0.14±0.13 MeV, respectively. The lifetime of the state is estimated to be (4.8±4.3)×${10}^{\mathrm{-}21}$ s.

Coulomb screening effects are studied in very-low-energy nuclear reactions. The two-potential formalism is shown to be a convenient method for the separation of long-range (molecular) and short-range (nuclear) dynamics. As specific applications, electron screening effects and muon catalysis in nuclear reactions are investigated. In the case of electron screening in very-low-energy nuclear reactions a method is elaborated for calculation of the enhancement of the astrophysical factor. For muon-catalyzed fusion reactions the sudden approximation is shown to be valid even if the reaction is dominated by a long-lived nuclear resonance.

This work addresses the question of how well, in principle and in practice, the electric and Coulomb quadrupole amplitudes for the N→Δ transition can be determined. The analysis is motivated by the significantly greater number of observables available in polarized electroproduction that will become accessible at the new generation of electron accelerators. The influence of several common assumptions, such as restriction to s and p waves only, is investigated. Results are presented for low [0.12 (GeV/c${)}^2$] and high [2.5 (GeV/c${)}^2$] four-momentum transfers.

The effect of Δ and ΔΔ degrees of freedom on the triton binding energy (${\mathit{E}}_{\mathit{T}}$) is studied using the Hannover ΔΔ force model. The three-body system of interest extends through J≤4, with L(NΔ),L(ΔΔ)≤4. A series of preliminary investigations reduces this three-body problem to J≤2, with L(NΔ),L(ΔΔ)≤2, and a 110 keV attractive correction to ${\mathit{E}}_{\mathit{T}}$. These J≤2 ΔΔ calculations reveal a repulsive dispersive effect of 930 keV and an attractive ΔΔ three-body force effect of 500 keV, in addition to the corresponding one-Δ effects of 550 and 920 keV, respectively. The total Δ-induced dispersive effect is thus about 1480 keV, while the total Δ-induced three-body force effect is about 1420 keV: Δ effects on ${\mathit{E}}_{\mathit{T}}$ almost exactly cancel. The net ΔΔ J≤2 result is ${\mathit{E}}_{\mathit{T}}$=7.32 MeV, while the corresponding nucleons-only result is 7.38 MeV. Similarly, the net J≤4 result is ${\mathit{E}}_{\mathit{T}}$=7.43 MeV, as compared to the corresponding nucleons-only result, 7.46 MeV. The Hannover ΔΔ force model is also examined for consistency with the two-body scattering parameters and is found to be somewhat defective in this regard. Thus, the important implications of these qualitative results for nuclear physics are to some extent dependent on confirmation using more sophisticated force models.

Cross sections have been calculated for the reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,η${)}^2$${\mathrm{H}}^{\mathrm{*}}$ in the impulse approximation. Very different cross sections are obtained for the T=1 and T=0 n-p breakup channels. This calculated difference demonstrates that the reaction can be useful in determining the isospin components of the electromagnetic transition amplitude of nucleon resonances with strong eta-decay branches. Measurements of this cross section will complement earlier data from ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,η${)}^2$H.