Theoretical results on the asymmetry function are provided to encourage measurements to further test the recent unexpected conclusion that nucleon polarization measurements in the photodisintegration of the deuteron at low gamma-ray energies do not appear to require the two-body exchange current contributions.

The influence of off-shell and nonlocal effects in the first-order nonrelativistic microscopic optical potential is investigated for elastic proton scattering above 100 MeV. With the free nucleon-nucleon $t$ matrix taken from the model of Love and Franey, these effects are significant only for scattering angles greater than about 60° and energies below about 300 MeV. The inadequacy of the standard first-order theory for predictions of spin observables at forward scattering angles remains unchanged when these effects are included and the need for higher order processes including medium and relativistic effects is reinforced.

Resonating group kernels for the nine-quark NNN system are used to show that the quark structure of nucleons leads to nonlocal three-body forces which are short ranged and attractive. They give a net contribution of 0.2 MeV to the three-nucleon binding energy, 0.9 MeV via quark-quark interaction terms whose effect is partially canceled by kinetic energy contributions to the exchange kernels.

A generalization of many-fermion Feynman-Goldstone diagrams is derived based on a time-dependent unperturbed Hamiltonian along with a time-dependent reference state. In lowest order, the time-dependent Hartree-Fock equations follow immediately from the same arguments which lead to static Hartree-Fock when the basis is time independent. Systematic corrections to the time-dependent Hartree-Fock mean-field approximation are obtained through higher order diagrams.

[NUCLEAR STRUCTURE Generalization of Feynman-Goldstone diagrams to a time-dependent reference state. Diagrammatic derivation of the time-dependent Hartree-Fock equations and their systematic corrections.]

A periodic time-dependent Hartree-Fock solution is used as the reference state for a diagrammatic expansion of the propagator. A discrete Fourier transform leads to a function of energy whose poles are the corresponding energy levels. Limiting the expansion to first-order diagrams leads to a new derivation of the Bohr-Sommerfeld-type quantization rule for collective states.

[NUCLEAR STRUCTURE Collective energies. Periodic time-dependent Hartree-Fock. Diagrammatic derivation of the Bohr-Sommerfeld quantization rule.]

Models of ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ are constructed from ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-{}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{}$ separable interactions fitted to low-energy two-nucleon properties. In particular, a set of ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-{}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{}$ interactions is used that produces $D$-wave components in the deuteron with $P_D=0\%\mathrm{to}10\%$. The ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ binding energy ($B_3$), ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ wave-function component percentages, ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d(${\mathrm{d}}^{*}$) asymptotic normalization constants, ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d distorted wave parameters, percentage n-d component in the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ wave function, and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d momentum distribution are calculated for each case. From these results, numerous aspects of the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d(${\mathrm{d}}^{*}$) vertexes are examined. As examples: (1) dependence of the $S$- and $D$-wave ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d asymptotic norms on $P_D$ and $B_3$; (2) dependence of the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+${\mathrm{d}}^{*}$ asymptotic norm on the scattering length and effective range of the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ interaction; (3) role of the $D$-wave component of the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d momentum distribution for n-d relative momentum between 0 and 2 ${\mathrm{fm}}^{-1\mathrm{}}$; and (4) validity of approximating the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d distorted-wave parameter, $D_2$, by the ratio of the $D$- to $S$-wave asymptotic normalization constants. Where possible, comparisons are made with local-potential calculations and experiment.

[NUCLEAR STRUCTURE Faddeev calculations. ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+d or ${}_{}{}^3{}_{}{}^{}\mathrm{H}$→n+${\mathrm{d}}^{*}$ vertex structure. Deuteron $D$-wave effects on ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ vertex structure.]

Diverse experimental information is analyzed to show that all the $N=82\mathrm{}$ isotones with $Z=58,60,62,64,66,68,\mathrm{and} 70$ are doubly "magic" nuclei. Also, nuclei in this region are shown to exhibit identical behavior, i.e., they are similar in many ways. The implications of this discovery for the interacting boson model and other areas of physics are discussed.

[NUCLEAR STRUCTURE $Z=58\mathrm{} \mathrm{to} 70$, $N=82\mathrm{}$ isotones, stability and magicity, seniority mixing.]

Deformed states in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, in which four nucleons are placed in the $1p$ shell, are considered. An interaction consisting of a Gaussian attraction and zero range density dependent repulsion is employed. The parameters are chosen so that the ground state energy of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is -28 MeV, and the oscillator length parameter $b$ is 1.4 fm. The method of variation after projection is employed, using the techniques of Evans and Elliot, to obtain the energies of $J=0^{+},2^{+},\mathrm{and} 4^{+}$ states. The results are studied as a function of the range of the Gaussian interaction. Connection is made with the more extensively studied problem of four-particle—four-hole states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$.

The structure of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ is studied in the alpha cluster model with parity and angular-momentum projection for several nucleon-nucleon interactions. The method differs from previous studies in that the states of positive and negative parity are determined without the customary restriction of the variational space to cluster positions with certain assumed symmetries. It turns out that a number of variational results in the literature are spurious under unrestricted variations. We demonstrate that the alpha cluster model of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ is capable of explaining most of the experimental $T=0\mathrm{}$ levels up to about 15 MeV excitation. In particular, the 6.05 MeV rotational band is reproduced remarkably well. A shell-model analysis of the excited cluster-model states shows the necessity of including a very large number of shells. The evidence for the recently proposed tetrahedral symmetry of some excited states is also discussed.

A method for projecting on angular momentum wave functions discretized on a three-dimensional Cartesian mesh is presented. The method is based on a matrix representation of the rotation operator. It is applied to cranked Hartree-Fock wave functions calculated for ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ with a simple interaction. In this case, the accuracy of the projected matrix elements is estimated to be of the order of 0.1%. An extensive comparison of the projected and cranking energies is made. The validity of the cranking method as an approximation to a variation-after-projection calculation seems to be wider than usually expected. The study of the fission barrier of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ for the channel ${}_{}{}^4{}_{}{}^{}\mathrm{He}$-${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ shows that the cranking predictions for these very deformed states are quite reliable.

The method of coherent correlated pairs is applied with a realistic effective Hamiltonian to the four-nucleon system. Three methods of solution are compared for ease of implementation and convergence rates. A Monte Carlo method yields the best upper bound within the coherent correlated pair space. The full variational treatment of the four-nucleon coherent correlated pair problem yields equations which have poor stability properties. An ansatz variational method proves to be rapidly convergent and yields results very close to those of the Monte Carlo method. The results for binding energy and the one body density distribution are compared with Hartree-Fock results using the same effective Hamiltonian in the same model space. As in previous soluble model applications the coherent correlated pair method provides a superior upper bound to the ground state energy.

A microscopic calculation of the second-order imaginary optical potential is made for ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$(p,p) at 14 MeV incident energy using random phase approximation transition densities for intermediate excited states. The sensitivity of the surface absorption on details of the nuclear structure wave functions is discussed.

The decay of mass-separated ${}_{}{}^{124}{}_{}{}^{}\mathrm{Ag}$ to ${}_{}{}^{124}{}_{}{}^{}\mathrm{Cd}$ was studied by $\gamma$ singles and $\gamma \gamma$ coincidence measurements. A half-life for ${}_{}{}^{124}{}_{}{}^{}\mathrm{Ag}$ of 0.17 ± 0.03 s was measured. The one $\gamma$ ray from ${}_{}{}^{124}{}_{}{}^{}\mathrm{Ag}$ decay observed at 613 keV is postulated to depopulate the $2_1^{}{}_{}{}^{+}$ state in ${}_{}{}^{124}{}_{}{}^{}\mathrm{Cd}$. The resulting extension of the systematics of even-even Cd isotopes is discussed.

[RADIOACTIVITY ${}_{}{}^{124}{}_{}{}^{}\mathrm{Ag}$, ${}_{}{}^{124}{}_{}{}^{}\mathrm{Cd}$ [from ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}(\mathrm{n},f)$]; measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$, $\gamma \gamma$ coin for ${}_{}{}^{124}{}_{}{}^{}\mathrm{Ag}$, ${}_{}{}^{124}{}_{}{}^{}\mathrm{Cd}$ measured $T_{\frac{1}{2}}$; Ge(Li) detectors; ${}_{}{}^{124}{}_{}{}^{}\mathrm{Cd}$ deduced levels $J$, $\pi$. Mass-separated ${}_{}{}^{124}{}_{}{}^{}\mathrm{Ag}$ and ${}_{}{}^{124}{}_{}{}^{}\mathrm{Cd}$ activity.]

The level structure of ${}_{}{}^{200}{}_{}{}^{}\mathrm{Hg}$ has been studied by the ($\mathrm{n},{\mathrm{n}}^{\prime }\gamma$) reaction. All previously identified levels below 2 MeV are confirmed, and some aspects of the low-lying structure have been clarified.

[NUCLEAR REACTIONS ${}_{}{}^{200}{}_{}{}^{}\mathrm{Hg}(\mathrm{n},{\mathrm{n}}^{\prime }\gamma )$, $E_n=1.0-3.5\mathrm{}$ MeV; measured $E_{\gamma }$, $I_{\gamma }$, $\sigma (E,E_{\gamma },{125}^{\circ })$, $\sigma (E_{\gamma },{\theta }_{\gamma })$. Deduced levels, $J$, $\pi$. Enriched target.]

Monochromatic photons derived from the ($n,\gamma$) reaction have been used to induce the ($\gamma ,n$) reaction from which several excited states in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$ have been deduced. The energies (in keV) and associated uncertainties for the levels observed are 39(2), 109(2), 179(2), 231(2), 258(2), 309(2), 365(3), 412(2), 442(2), 466(3), 515(3), 542(2), 571(2), 624(2), 643(2), 666(3), 720(2), 793(2), 820(2), 857(2), 897(3), 959(3), 1122(2), 1205(2), 1247(3), 1307(2), 1351(2), 1427(4), 1740(3), 1822(3), and 1866(3). The photoneutron cross sections for the formation of these states via various photon energies are also given.

[NUCLEAR REACTIONS ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}(\gamma ,n){}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$; ($n,\gamma$) photons; measured $E_{\mathrm{n}}$; deduced level energies.]

We treat the phase shift problems of the elastic scattering of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ ($E_{\mathrm{lab}}=60\mathrm{}$ MeV), ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ($E_{\mathrm{lab}}=50\mathrm{}$ MeV), and $\alpha +{}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ($E_{\mathrm{lab}}=104\mathrm{}$ MeV) in a similar manner. We calculate the contributions to the zeroth order as well as the first order in ${\hslash }^2$. We find that the results approach the exact ones as they should.

[NUCLEAR STRUCTURE WKB method for phase shifts.]

We study the spatial correlations between two particles (or two holes) around a closed shell core in terms of the probability distribution expressed as a function of the c.m. coordinate $R$ of the two particles and of their relative coordinate $r$. We find that the mixing of configurations induced by the pairing force leads to a probability distribution centered in regions corresponding to larger values of $R$ and smaller values of $r$, as compared to the case of a pure ${\mathrm{}\left(j\right)\mathrm{}}_0^2$ configuration. This tendency to a "surface clustering" is mainly due to the interference of the contributions coming from levels with different parity. However, even with the inclusion of a large number of configurations, the size of the localized "cluster" is much larger than that of a free dinucleon system.

[NUCLEAR STRUCTURE Pairing correlations, correlation in space, two-particle transfer reactions.]

The effect of the deuteron breakup channel on the elastic scattering of deuteron lead targets around 80 MeV incident deuteron energy has been examined. It is found that the large difference between experimental values and folding model predictions could mostly be explained in terms of deuteron breakup effects.

[NUCLEAR REACTIONS d-${\mathrm{Pb}}^{208}$ elastic scattering, $E_{\mathrm{d}}=79.4\mathrm{}$ MeV breakup channel effects.]

The effect of crossing symmetry on the $P_{11}$ channel of the pion-nucleon system is investigated. A static model is constructed which includes attraction from the crossed delta graph, rho exchange, and crossing from the $p$ waves. After fitting the phase shifts, it is found that crossing plays an important role in this channel. The crossing contribution is 25% of the total attractive part of the amplitude at the zero in the phase shifts and 20% at the Roper resonance. This large effect is expected to persist at low energies when relativistic corrections are made.

[NUCLEAR REACTIONS $\pi \mathrm{N}$ scattering in $P_{11}$ channel, crossing symmetry, Roper resonance.]

The fragmentation theory is used to study the fine structure effects in nuclear fission charge distribution yields. The odd-even proton effects as well as the resulting non-Gaussian charge distributions are shown to be given satisfactorily, without use of any free parameter. Calculations are made for light mass products 98, 100, 102, and 104 due to thermal neutron induced fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$.

[NUCLEAR REACTIONS, FISSION Charge distributions, non-Gaussian, fine structure, odd-even proton effects, post saddle shape, fragmentation dynamics, light mass chains, ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$.]