We analyze the ${\pi }^0$ photoproduction near threshold on spin- and isospin-zero nuclei within the elementary particle approach. From ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ data, we find that model independent contributions are very small. This makes the analysis of different models quite clear. Thus, while individual excited nuclear states contribute negligibly, the meson exchange correctly describes the data. Measurements of the mass number dependence of the meson-nuclei couplings would test these ideas.

High energy electrons and positrons observed in medium energy nucleus-nucleus collisions are shown to be primarily due to the external conversion of high energy gamma rays. The reaction ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$+Cu was studied at E/A=40 MeV, and a magnetic spectrograph was used with a specially constructed multiwire proportional counter plus Cerenkov detectors. A stopping target yield of 1.8±0.6×${10}^{\mathrm{-}6}$ photons with $E_{\gamma }$>25 MeV was measured per incident beam particle. The direct yield of $e^{+}$$e^{\mathrm{-}}$ pairs is less than 2% of the gamma yield.

The neutron total cross section of ${}_{}{}^{48}{}_{}{}^{}$Ca+n has been measured up to 10 MeV and analyzed up to 4 MeV using the R-matrix formalism to obtain resonance parameters and potential scattering phase shifts. Very little s-wave neutron strength was observed, and the small cross section (0.5±0.2 b) observed for low-energy neutrons (<150 keV) can be described by a real Woods-Saxon potential with $V_0$=47.3±0.7 MeV, $r_0$=1.21 fm, and a=0.66 fm. Three strong $d_{5/2}$ resonances amounting to 45% of the single-particle width were found in the 0.8- to 2.0-MeV energy region. These results compare well with cross-section predictions from two microscopic calculations. The $p_{1/2}$, $p_{3/2}$, and $d_{3/2}$ resonance strengths are very weak (much smaller than the $d_{5/2}$ strength).

The asymmetry dependence of the incompressibility at fixed density, the density at fixed pressure, and the isobaric incompressibility are studied for neutron-rich nuclear matter at arbitrary densities. Simple expressions valid to all orders in density and to second order in asymmetry are derived involving the density derivatives of the Landau parameters of the symmetric system. Illustrative calculations are performed with different equations of state.

Differential cross sections for neutron elastic scattering from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ have been measured in the energy range 18–26 MeV. These data, together with previously published neutron and proton data for these nuclei and for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ in the energy region 20 to 65 MeV, have been analyzed in terms of two microscopic optical potentials. The spherical potential derived from the work of Jeukenne, Lejeune, and Mahaux provides a consistent representation of the differential data, provided the imaginary central potential is renormalized. Predictions from the interaction of Brieva and Rook give less satisfactory agreement. In particular, there is a significant overprediction of the forward angle data below ∼25 MeV and an underprediction above ∼35 MeV.

A separable approximation to a two-body interaction is constructed from Gamow states. It was found possible to reproduce on- and off-shell quantities of a solvable model with good accuracy and without the occurrence of spurious zero with resonances. No free parameters were introduced to achieve these results.

The gamma ray to proton branching ratio, ${\Gamma }_{\gamma }$/${\Gamma }_{\mathrm{p}}$, of the ${}_{}{}^2{}_{}{}^{}$H${+\mathrm{}}^3$He reaction has been measured between center-of-mass energies of 25 and 60 keV. The ratio of the ground-state gamma reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}$${(}^3$He,${\gamma }_0$${)\mathrm{}}^5$Li to the dominant reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}$${(}^3$He,p${)}^4$He is observed to be roughly constant over this energy range with a best value of (4.5±1.2)×${10}^{\mathrm{-}5}$. This ratio for the gamma-ray reaction to the ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$ first excited state is measured to have a value of (8±3)×${10}^{\mathrm{-}5}$. The excitation energy of the first excited state is estimated to be 3.0±1.0 MeV.

Measurements of width and amplitude correlations allow sensitive tests of the amplitude distribution. Experimental results show an apparent discrepancy from the expected multivariate Gaussian distribution. A test which shows that the disagreement cannot be explained solely by the limited sample sizes is presented.

An alternate way of introducing inelasticity parameters for two coupled elastic channels, such as the S and D waves in np scattering, has been devised. The present scheme is related to recent proposals of Bryan, of Klarsfeld, and of Melhem and Kermode. The existence of spurious solutions in the purely elastic case is demonstrated and a cure proposed.

Cross sections for production of Li and Be isotopes in the α(α,pn${)}^6$Li, α(α,p${)}^7$Li, and α(α,n${)}^7$Be reactions have been measured at 198.4 MeV. These measurements are relevant to the understanding of light-element nucleosynthesis in galactic cosmic ray interactions with the interstellar medium. The data indicate that beyond energies of about 250 MeV, the α+α reaction does not contribute to the natural abundance of lithium, reinforcing theories which produce ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ in cosmic ray processes and most of nature’s ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ in the big bang. In addition, α+α elastic scattering data obtained in these experiments have been analyzed in terms of the optical model, and the results are compared with lower-energy systematics.

The ${}_{}{}^{36}{}_{}{}^{}\mathrm{S}$(t,p${)}^{38}$S reaction was studied at 18-MeV bombarding energy with an overall energy resolution of 55 keV. Excited states of ${}_{}{}^{38}{}_{}{}^{}\mathrm{S}$ were identified at energies (uncertainties in parentheses) of 1295(10), 2835(14), 3375(17), 3690(17), 4336(20), 4478(22), 4955(25), 5064(27), 5278(28), 6000(30), and 6605(60) keV. Angular distributions were measured for protons leading to the ground state and ten lowest excited states. The data are compared with distorted-wave Born approximation calculations in which a microscopic two-nucleon form factor was employed. On this basis spin assignments have been made for several states. A comparison is made between levels observed in ${}_{}{}^{38}{}_{}{}^{}\mathrm{S}$ and those predicted by the weak coupling and shell models.

Inclusive proton spectra were measured from the interaction of 150 MeV protons with a variety of targets ranging from berylium to bismuth over the angular range from 10° to 30°. At all of the angles at which data were taken the spectra from the berylium and the carbon targets show strong peaks attributable to quasifree scattering while the spectra from nickel and heavier targets are rather flat throughout the continuum region. The quasifree scattering is calculated using a Fermi gas model, with the nucleus a uniform sphere, and in this picture the required attenuation of a quasifree peak requires a nucleon free path of no more than about 3.5 fm. Spectra of deuterons, tritons, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, and alpha particles were also measured.

This paper investigates the ability of an $L^2$ discretization procedure to approximate three-body continuum effects using a finite dimensional Sturmian basis. The approximation is tested in three-body connected kernel equations of the Alt-Grassberger-Sandhas–type. The numerical accuracy of the approximate $L^2$ discretized equations is tested by solving a model problem of three bosons interacting via S-wave nonseparable potentials. The potentials are either an attractive Yukawa function, or a sum of two Yukawa functions, one attractive and one repulsive. Numerical results are compared with those of three-body calculations for energies below the breakup threshold. It is found that three-body, connected kernel equations respond remarkably well to the $L^2$ discretization procedure both on and off shell.

The neutron capture cross sections of 198,199,200,201,20 2,204Hg(n,γ) were measured in the energy range 2.6 to 500 keV. The average capture cross sections were calculated and fitted in terms of strength functions. Resonance parameters for the observed resonances were determined by a shape analysis. Maxwellian averaged capture cross sections were computed for thermal energies kT between 5 and 100 keV. The solar mercury abundance was determined to be 0.34±0.04 relative to Si${=10\mathrm{}}^6$. The termination of s-process nucleosynthesis at lead and bismuth was investigated. The abundances of ${}_{}{}^{206}{}_{}{}^{}$,207,208Pb were reproduced introducing a strong fluence component of the s process in addition to normal s- and r-process nucleosynthesis. The radiogenic ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ abundance was determined and the r-process age was calculated via ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. Using Fowler’s exponential model, an age T=4.6 Gyr +Δ=17.2±2.6 Gyr was obtained.

The ${}_{}{}^{40}{}_{}{}^{}$,42,44Ca, ${}_{}{}^{46}{}_{}{}^{}$,48,50Ti, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Cr}$, and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$ (t${,}^3$He) reactions have been studied at $E_{\mathrm{t}}$=25 MeV. Differential cross sections have been measured in the angular range ${\theta }_{\mathrm{lab}}$=5.5°–50°. The angular distributions have been compared with coupled-channels calculations. J ${}_{}{}^{\pi }{}_{}{}^{}$ assignments have been made to a number of states in the residual nuclei ${}_{}{}^{40}{}_{}{}^{}$,42,44K, ${}_{}{}^{46}{}_{}{}^{}$,48,50Sc, ${}_{}{}^{54}{}_{}{}^{}\mathrm{V}$, and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$.

The yields of protons and α particles from 2 mg/${\mathrm{cm}}^2$ targets of ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{92}{}_{}{}^{}\mathrm{Zr}$ have been measured in the incident electron energy range 20–100 MeV; the ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$(e,p) and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$(e,α) data were extended to 130 MeV. Photodisintegration plus electrodisintegration yields were also measured for electron energies above 50 MeV. The photodisintegration cross sections, derived from these data, rise continuously from 25 MeV onward for all four reactions. One satisfactory explanation of this phenomenon is that we are observing multiparticle emission following virtual photon absorption.

A microscopic model for the alpha-particle-nucleus optical potential is presented and applied to α${\mathrm{-}}^{40}$Ca scattering. Starting with the M3Y force as the basic nucleon-nucleon interaction, the single-channel contribution to the optical potential is calculated by means of the fish-bone model which treats the antisymmetrization between the projectile and the target nucleus in an approximate way. The applicability of the fish-bone model to the α${\mathrm{-}}^{40}$Ca system is tested by comparison of resonating group calculations with fish-bone model calculations. The potential terms arising from the coupling of the elastic channel to other reaction channels have been calculated in the framework of the nuclear structure approach using random-phase approximation transition densities for intermediate excited states. The elastic scattering cross sections calculated from the microscopic potentials reproduce gross structures of the experimental data. However, the model cannot account for the whole absorption.

Gamow-Teller allowed neutrino capture transitions between the ground state of ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ and accessible excited states in ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$ are calculated in a model space of the 2p and 1f shells. The total (p,n) Gamow-Teller strength function is also calculated. The effects of model-space truncation are systematically investigated and detailed comparisons are made between calculated and experimental spectroscopic data for states in ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ and ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$. The calculated effect of excited-state transitions is in good agreement with a previous phenomenological estimate (based upon beta decay measurements in the vicinity of mass 71) except for the higher energy ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ neutrinos. For these rare high energy neutrinos, there is not yet sufficient experimental information to make a complete phenomenological estimate. The total cross section for ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ neutrinos is calculated to be about ten times larger than the ground-state–to–ground-state capture rate. The overall uncertainty in the capture rate for a ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ detector that is caused by excited state transitions is estimated to be about 5 percent for a standard solar model and about 1 percent for nonstandard models that are consistent with the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ solar neutrino experiment.

A study of the π1$g_{9/2}$ orbit size in ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$ is presented. The rms radius for the point-proton density is extracted by studying transitions to $8^{+}$ states in these nuclei. The radii are consistently larger than a value determined in a magnetic electron scattering experiment on ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$. A qualitative discussion of the ground state occupation of the π1$g_{9/2}$ orbit based on the transition amplitudes to the $8^{+}$ states is given.