Within the unitary πNN theory with Δ excitation, the effect of πd and πNN production channels on NN elastic scattering is examined. It is shown that the two-body coupled-channel method, which has been widely employed to study the Δ excitation in intermediate-energy NN scattering, is a valid approximation. Our results indicate that the difficulty encountered by the meson-exchange theory in understanding the NN data up to 1 GeV cannot be resolved within the model based on the one-pion-exchange Δ excitation mechanism.

We construct nucleon knockout amplitudes which exactly satisfy probability current conservation. The derivation is first produced for a nucleon bound to an inert core and is then generalized to the case of realistic nuclei. Numerical tests are presented for a nucleon bound in a square well potential for which exact results are compared with several approximated ones; the need of imposing probability current conservation is also numerically demonstrated.

Continuum spectra for pion single charge-exchange scattering at 165 MeV kinetic energy are calculated for a number of nuclei within the single-scattering approximation over a wide range of nuclear excitation energy. The discrepancy between our calculations and the data suggests that multiple-scattering processes may contribute significantly to the charge-exchange spectra. This suggestion is consistent with the present understanding of the delta-nucleus interaction as given, for example, by the isobar-hole model.

The NN-πNN equations that describe, in a unified framework, pion production in nucleon-nucleon scattering, and pion-deuteron and nucleon-nucleon elastic scattering, have been extended to include the N(939) and Δ(1232) on an equal footing. This extension, motivated by the quark models of hadrons, has the bare N and Δ as three quark states with the same spacial wave function, but different spin isospin states. The final equations, referred to as the BB-πBB equations, are consistent with the chiral bag models to the extent that the πNN, πNΔ, and πΔΔ coupling constants and form factors are related, and can be taken from bag models. The resultant equations satisfy two- and three-body unitarity, and are derived by exposing the lowest unitarity cuts in the n-body Green’s function. These equations retain important contributions missing from the NN-πNN equations. For pion production and N-N scattering they include the contribution of backward pions in the NN→NΔ transition potential, which may overcome the problem of small pp→πd cross section as predicted by the NN-πNN equations. For π-d elastic scattering they include an additional NΔ→NΔ tensor force that can influence the tensor polarization.

An analysis is carried out of a π-N-Δ field theory using projection operator techniques developed recently by the author. Relationships are derived between matrix elements of resolvents formed from bare ππN and ππΔ states and various three-particle amplitudes. These relations are exactly analogous to those obtained in potential theory between the three-particle Green’s function and the transition operators of Alt, Grassberger, and Sandhas. When the three-particle amplitudes are integrated over with appropriate weighting functions, the elastic scattering and production amplitudes are obtained. The weighting functions are the analogs of bound state wave functions for the πN and πΔ subsystems. A separation of the production amplitude into its one-fermion irre- ducible and reducible parts is derived. It is shown that the three-particle amplitudes are solutions of AlT, Grassberger, and Sandhas type of equations as extended by Kowalski to allow for a three-body interaction. When the AlT, Grassberger, and Sandhas quasiparticle method is applied to these equations, the two-particle equations developed previously by the author are recovered. If the one-fermion irreducible part of the three-body interaction is neglected a closed set of coupled nonlinear integral equations for all of the quantities of interest is obtained.

The spontaneous emission of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ from ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$, recently discovered by Rose and Jones, has been confirmed, and the mass of the emitted particles unambiguously identified. The present measurement was performed with a ${}_{}{}^{227}{}_{}{}^{}\mathrm{Th}$ source containing 9.2 mCi of ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$. An Enge split-pole magnetic spectrograph was used to suppress the intense alpha radiation and to identify the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ particles. The spectrograph was calibrated with tandem-accelerated beams of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. In six days of decay counting, twenty-four ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ events were observed yielding a branching ratio of (4.7±1.3)×${10}^{\mathrm{-}10}$ for the emission of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ from ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$ relative to that of alpha particles. The value is in fair agreement with the result of Rose and Jones, (8.5±2.5)×${10}^{\mathrm{-}10}$, and with more recent measurements from other laboratories.

Double ionization of the atomic K shell accompanying the K-shell internal conversion of the 0.145-MeV transition of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ has been studied by recording coincidences between Kα satellite x rays and Kα hypersatellite x rays emitted when the double vacancies are filled. The probability per K-shell internal conversion that a double vacancy is formed, $P_{\mathrm{KK}}$(IC), was found to be (3.4±0.3)×${10}^{\mathrm{-}5}$, which is a factor of (0.79±0.07) times the theoretical prediction for K-shell electron shakeoff in K-shell internal conversion of Mukoyama and Shimizu. The K${\alpha }_1$ to K${\alpha }_2$ hyper- satellite ratio was found to be (1.50±0.13), a value which is about 6% less than the calculation of Åberg et al.

A new fluid dynamical description of giant resonances which avoids the scaling approximation and takes into account the interplay between first sound and zero sound is presented. The new method leads to equations satisfying the sum rules $S_{\mathrm{-}1}$, $S_1$, and $S_3$ for the electric modes and the sum rule $S_1$ for the magnetic modes. The model describes surface modes and separates the low lying modes from the giant resonances. Numerical results for the energy spectrum of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are presented.

Isotope shifts of the stable strontium isotopes ${}_{}{}^{84}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{86}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{87}{}_{}{}^{}\mathrm{Sr}$, and ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$ and the radioactive isotopes ${}_{}{}^{89}{}_{}{}^{}\mathrm{Sr}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Sr}$ have been measured using laser spectroscopy on collimated atomic beams. The changes in mean square charge radii extracted from the isotope shifts show a pronounced shell effect at the closed neutron shell N=50. The experimental data are compared with the predictions of the droplet model and Hartree-Fock plus BCS calculations. The analysis suggests that the changes in mean square charge radii are due to a change in size, a change in the predominantly dynamic deformation, and a change in the diffuseness of the nuclear charge distribution.

The accuracy of the optimal subset approximation, which reduces the number of coupled equations in the hyperspherical harmonic method, is checked theoretically and numerically. The critical parameter that determines the error of the method is shown to be proportional to the product of potential matrix elements connecting the K=0 state to states with K>0, and the matrix elements between K>0 states. In particular this means that the accuracy is largely independent of the degree of excitation of the system. The numerical precision of the optimal subset method in calculating energies and expectation values of Coulomb-bound three-body systems is checked by comparison of optimal subset results with exact results for fixed maximum global angular momentum $K_{\max }$. Errors range from less than one percent for the helium atom ground state energy to 100 percent or more for certain positronium ion expectation values. This precision is consistent with the theoretically determined error parameters.

Impulse approximation and pion-exchange current contributions to the trinucleon magnetic moments are calculated using wave functions generated by solving the configuration-space Faddeev equations for a variety of nucleon-nucleon force models. Careful attention is paid to the origin of important exchange current contributions. Numerical results are compared with previously published calculations and with the experimental data. An attempt is made to isolate and understand sources of discrepancy between our results and those previously published. Calculations which include both impulse and pion-exchange current contributions are in fairly good agreement with experiment, whereas calculations which include only the impulse approximation term are not.

A supersymmetry scheme for nuclei, where neutron and proton bosons are distinguished, is presented. The single j for this scheme is assumed to be (3/2) and therefore the resulting supergroup is U(12/4). The dynamical supersymmetry investigated is the Spin(6) chain. This scheme is a direct generalization of the U(6/4) supersymmetry scheme previously proposed by Iachello and co-workers. Comparisons of the energies between the theory and experiment seem to suggest that such a supersymmetry U(12/4) may be found in certain regions in nuclei.

We report upon calculations of a complete set of response functions for nuclear matter. The calculations are performed in the Tamm-Dancoff approximation using a reaction matrix calculated with a realistic interaction. (This interaction was obtained in the application of the one-boson-exchange model to the description of nucleon-nucleon scattering.) We stress the importance of performing such calculations with realistic interactions. We also indicate that a reasonable result for the response in the scalar-isoscalar channel can only be obtained using an effective interaction that saturates at the correct density for nuclear matter. Therefore, we calculate the reaction matrix in the scalar-isoscalar channel using the recently developed relativistic Brueckner-Hartree-Fock theory. (Relativistic effects are less important in other channels and are neglected in these calculations in all channels other than the scalar-isoscalar channel.) We find zero-sound modes in several channels for excitations of small momentum. We also study the evolution of the nuclear response for increasing values of the momentum, in the range 0$k_F$≤1.0, or 0$k_F$≤1.5 in some cases, and discuss the recent data on the ratio of the spin-dependent longitudinal to the transverse response for proton scattering on ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.

Many microscopic studies of both nuclear matter and s-shell nuclei have been undertaken with recently developed realistic models of the nucleon-nucleon interaction. These studies have proven to be very useful in enhancing our understanding of nuclear structure. Microscopic treatment of all but these lightest nuclei (A<5) has proven to be extraordinarily difficult, however, because of the strong spin-isospin dependence of the interaction. We have developed a new method of performing variational calculations with realistic interactions for larger nuclei. This method does not rely upon spin and spatial symmetries of the system, as in nuclear matter calculations, or upon explicit summation over all spin states, as has been done in s-shell nuclei. Instead spin-isospin states are sampled in a random walk which takes place in a combination of spin, isospin, and coordinate space. Results of calculations of the oxygen nucleus with a V6 interaction are reported, including energy, form factor, and charge distribution.

Finite temperature effects in the pairing force problem are studied within the formalism of a variational approach. The formalism, which is free of the number fluctuations which are present in the standard Bardeen-Cooper-Schrieffer approach, allows for the description of thermally-induced phase transitions. An application of the method is discussed for the case of a two-level model.

The nuclear structure calculations for strontium, zirconium, and molybdenum isotopes are performed in a large configuration space by employing a quadrupole-plus-pairing-interaction Hamiltonian. The possible factors responsible for the sudden onset of deformation at N=60 in these nuclei are pointed out from the systematics of the occupancies of the single particle orbitals derived from the variational microscopic calculations. The energy spectra and the B(E2) values in the doubly even ${}_{}{}^{98}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{100}{}_{}{}^{}$,102Zr, and ${}_{}{}^{104}{}_{}{}^{}$,106Mo obtained from the variation-after-projection formalism are in good agreement with the corresponding experimental data.

Projected Hartree-Fock-Bogoliubov calculations employing renormalized effective interactions are carried out to estimate the proton-neutron occupancies of spherical shells in the ground states of several 2p-1f shell nuclei. The results are compared with the predictions obtained via the spectral distribution methods as well as with the available experimental estimates.

A boson expansion formalism in the seniority scheme is presented and its relation with number-conserving quasiparticle calculations is elucidated. Accuracy and convergence are demonstrated numerically. A comparative discussion with other related approaches is given.

The nuclear matter parameters and single-particle properties are calculated in the so-called ${\Lambda }^{\mathrm{}\left(00\right)\mathrm{}}$, ${\Lambda }^{\mathrm{}\left(10\right)\mathrm{}}$, and ${\Lambda }^{\mathrm{}\left(11\right)\mathrm{}}$ approximation of the Green’s function theory. For the nucleon-nucleon interaction we used the Hamada-Johnston, the Reid-soft-core, and the Paris potential. The results show no significant differences with those obtained from the Brueckner theory. For comparison we used also the Galitskii approximation.

An investigation of the thermal neutron radiative capture reaction ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$(n,γ${)}^{32}$P has yielded data with high statistical precision. Ninety-eight transitions have been assigned to a derived decay scheme and the neutron separation energy was found to be 7935.70(4) keV. Three E2 transitions have been identified with average strength B(E1)↓¯${=4.2\mathrm{}}_{\mathrm{-}2.5}^{+1.6\mathrm{}}$ $e^2$${\mathrm{fm}}^4$/MeV. This value is consistent with the Axel-Brink hypothesis.