We performed an experiment which was much more sensitive to the ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}(e, e^{\prime }\alpha )$ reaction at 13.1 MeV incident electron energy than was a previous experiment which reported surprisingly large cross sections. Our results set an upper limit for the ($e, e^{\prime }\alpha$) cross section of about 16 μb, an order of magnitude smaller than that reported earlier.

NUCLEAR REACTIONS ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}(e, e^{\prime }\alpha )$; $E=13.1\mathrm{}$ MeV; measured ${\sigma }_{e,\alpha }\mathrm{}\left(E\right)\mathrm{}$.

Within the framework of a microscopic theory for the multipole resonances in light deformed nuclei, the radiative capture reaction ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}(p, \gamma ){}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ is being studied. Accent is being put on improving the formalism of the theory as well as on gauging the relative importance of the quadrupole transitions as compared to the dominant dipole ones. From the results obtained for the cross sections and angular distributions it is seen that the reaction runs predominantly through the giant dipole states. The isoscalar quadrupole resonance is only weakly excited even though intermediate states with large $B\left(E2\mathrm{}\right)\mathrm{}$ values are available. The result may help to understand why in proton radiative capture reactions one detects a different $E2\mathrm{}$-strength distributions as compared to what is observed in $\alpha$-induced experiments.

NUCLEAR STRUCTURE ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$; calculated spectra, $E1\mathrm{}$ and $E2\mathrm{}$ transitions. Angular momentum projected deformed ph model.

NUCLEAR REACTIONS ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}(p, \gamma )$; calculated cross sections to ground and first excited states. Giant dipole and quadrupole resonances in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$.

Previous calculations have shown that the accurate prediction of two-nucleon overlap factors requires the inclusion of very large numbers of highly excited configurations. These "extended basis shell model" calculations treat a pair of nucleons added to an inert core. In the present paper, the two-particle random-phase approximation theory of Vary and Ginocchio is used to generalize the extended basis shell model to include the effect of core correlations. Including them is shown to have a small effect on two-nucleon stripping reactions, such as ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(t, p){}_{}{}^{18}{}_{}{}^{}\mathrm{O}$. However, the random-phase approximation enables us to include the effect of the highly excited single-particle states on the transition amplitudes for the pickup of a pair, e.g., ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(p, t){}_{}{}^{14}{}_{}{}^{}\mathrm{O}$. Because the admixed states have wave functions which are large in the surface and exterior regions, they result in large enhancements of pickup cross sections. We have also studied the breakdown of the random-phase approximation, when eigenvalues become complex. We provide a proof, for an arbitrary two-body interaction, that the potential strength for which the random-phase approximation eigenvalues become complex, is the minimum strength for which nontrivial solutions to the Hartree-Fock-Bogolyubov equations exist.

NUCLEAR REACTIONS Core correlations included in EBSM calculations of two nucleon stripping reactions using particle-RPA; influence of EBSM on two nucleon pickup reactions; breakdown of RPA.

Experimental results of mass measurements for all medium and heavy nuclei have been analyzed using a semiempirical mass formula. The analysis indicates the existence of a universal dependence on the neutron number for the shell-effects term in the neutron separation energies, and the existence of a similar universal dependence on the proton number for the shell-effects term in proton separation energies.

NUCLEAR STRUCTURE Medium and heavy nuclei, binding energies, shell effects, systematics.

The structures of the odd-$A$ Nb isotopes ${}_{}{}^{93,95,97}{}_{}{}^{}\mathrm{Nb}$ are studied in a semimicroscopic model which couples the proton quasiparticle motion to the quadrupole and the octupole vibrations of the neighboring even core. Inclusion of the octupole vibration of the core improves the $l=3\mathrm{}$ spectroscopic strength distribution of the earlier theoretical studies. There is a satisfactory agreement between the calculated and experimental level spectra, spectroscopic factors, and electromagnetic transition rates.

NUCLEAR STRUCTURE ${}_{}{}^{93,95,97}{}_{}{}^{}\mathrm{Nb}$, calculated levels $J$, $\pi$, $B\left(E2\mathrm{}\right)\mathrm{}$, quasiparticle-phonon coupling.

The application of the delta-shell method to finite-range distorted-wave Born-approximation calculations for low-energy ($d, p$) reactions is discussed. It is shown that this method is superior to the commonly used local-energy approximation as far as calculational accuracy is concerned.

NUCLEAR REACTIONS DWBA theory, finite-range effects.

An $S$-matrix analysis of the integrated and differential cross sections of the reaction ${}_{}{}^6{}_{}{}^{}\mathrm{Li}(n, t)\alpha$ over the energy range 0-3.9 MeV shows that the first $\frac{3}{2^{-}}$ excited state of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ should be situated at about 8.87 MeV. This value is lower than the one obtained in previous parametrizations.

NUCLEAR REACTIONS $S$-matrix analysis, ${}_{}{}^6{}_{}{}^{}\mathrm{Li}(n, t)\alpha$, $E_n$ up to 3.9 MeV, integrated and differential cross sections; first $\frac{{}_{}{}^{-}{}_{}{}^{}3}{2}$ excited level of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ located at ${\mathrm{E}}_x=8.87\mathrm{}$ MeV.

The systematic energy dependence of recently published surface-transparent potentials is shown to be affected very little by the coupling to the first excited $2^{+}$ state in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, although the elastic scattering cross sections depend quite strongly on the coupling.

NUCLEAR REACTIONS ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, elastic and inelastic $\sigma \left(\theta \right)$, coupled channels analysis.

We study the truncated $t$-matrix approximation for the triplet nucleon-nucleon interaction in the trinucleon bound state problem, where binding energies are found to be within 8% of the exact result. Numerical results in this approximation for the four-body bound state energy are also quoted.

NUCLEAR STRUCTURE ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, Faddeev-Yacubovsky calculation, bound state energies.

The directional correlations of the 135.3-32.2 keV and the 135.3-30.6 keV $\gamma -\gamma$ cascades in ${}_{}{}^{201}{}_{}{}^{}\mathrm{Hg}$ (following electron capture decay of ${}_{}{}^{201}{}_{}{}^{}\mathrm{T}1\mathrm{}$) were measured using a 5 cm × 5 cm NaI(T1) detector and a 78.5 ${\mathrm{mm}}^2$ × 5 mm Si(Li) detector. The results obtained were $W\left(\theta \right)=1+(0.184\mathrm{}\pm 0.030)P_2\left(cos\theta \right)$ and $W\left(\theta \right)=1+(0.175\mathrm{}\pm 0.040)P_2\left(cos\theta \right)$, respectively. Starting with the known ground-state spins of ${}_{}{}^{201}{}_{}{}^{}\mathrm{T}1\mathrm{}$ and ${}_{}{}^{201}{}_{}{}^{}\mathrm{Hg}$, the directional correlations give results consistent with the following spin assignments; $\frac{3}{2^{-}}\left(0\mathrm{} \mathrm{keV}\right)$, $\frac{3}{2^{-}}\left(1.6\mathrm{} \mathrm{keV}\right)$, $\frac{3}{2^{-}}\left(32.2\mathrm{} \mathrm{keV}\right)$, and $\frac{3}{2^{-}}\left(167.4\mathrm{} \mathrm{KeV}\right)$. Assuming that the 135.3-keV $\gamma$ transition is $M1+0.1\%$ $E2\mathrm{}$ (which is consistent with internal-conversion measurements), the directional correlation results are consistent with multipolarities of $M1+\le 0.3\%$ $E2\mathrm{}$ for the 32.2-keV $\gamma$ ray and $M1+\le 0.4\%$ $E2\mathrm{}$ for the 30.6-keV $\gamma$ ray. The corresponding values of the mixing ratios are $-0.0634\mathrm{}\le \delta \mathrm{}\left(30.6\right)\mathrm{}\le 0.0515$ and $-0.0361\mathrm{}\le \delta \mathrm{}\left(32.2\right)\mathrm{}\le 0.0506$. These results are in mixed agreement with previous measurements.

RADIOACTIVITY ${}_{}{}^{201}{}_{}{}^{}\mathrm{T}1\mathrm{}$; measured $\gamma \gamma \left(\theta \right)$. ${}_{}{}^{201}{}_{}{}^{}\mathrm{Hg}$ deduced $J^{\pi }$. Si(Li) and NaI(T1) detectors.

Proposed spin and parity of the states 2450.9, 2561.33, and 3415.7 keV in ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$ could be confirmed by $\gamma$ angular distribution and linear polarization measurements. The assignments of the states 3666.1 and 3954.5 keV could be corrected to $6^{-}$ and $7^{-}$.

NUCLEAR REACTIONS ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, 2p\gamma )$ ${}_{}{}^{67}{}_{}{}^{}\mathrm{Zn}(\alpha , n\gamma )$, ${}_{}{}^{68}{}_{}{}^{}\mathrm{Zn}(\alpha , 2n\gamma )$; measured $\gamma$ angular distributions and linear polarization, ${\chi }^2$ analysis.

Weak coupling calculations that correctly describe the 4p-2h states of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ invariably predict the presence of 6p-4h excitations beginning near 7 MeV. We suggest candidates for the $0^{+}$, $2^{+}$, $4^{+}$, and $6^{+}$ 6p-4h levels.

NUCLEAR STRUCTURE ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$; calculated excitation energies of 4p-2h and 6p-4h levels. Candidates for 6p-4h given.

The phenomenological isobar doorway model of Kisslinger and Wang is applied to the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\gamma , {\pi }^0){}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ for photon energies between 220 and 360 MeV. The parameters of the model are determined by fitting pion elastic scattering data. Over most of thee energy range the isobar model gives a total photoproduction cross section substantially larger than distorted-wave impulse approximation with a static first order optical potential. The calculated cross sections are compared to experimental data at photon energy 250 MeV.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{-}, {\pi }^{-})$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\gamma , {\pi }^{\circ })$, resonance region, isobar doorway model.

A technique for approximating local interactions by separable interactions of simple analytic form is examined. Approximations to an exponential potential are calculated. Near zero energy, where the local potential possesses an antibound state, a rank three potential is required to produce a reasonable approximation. The unique feature of the approximation proposed here is that it can produce separable potentials whose scattering amplitudes are good approximations near a predetermined energy. The range of validity of the approximation is found to expand rapidly as one increases the rank of the potential.

NUCLEAR REACTIONS Scattering theory, approximating local potentials by separable forms.

We have studied the level structure of ${}_{}{}^{173}{}_{}{}^{}\mathrm{Tm}$ via the ${}_{}{}^{176}{}_{}{}^{}\mathrm{Yb}(p, \alpha ){}_{}{}^{173}{}_{}{}^{}\mathrm{Tm}$ reaction. We measure the excitation energies of 32 states up to 2.192 MeV. Twenty-seven of these states have not been reported previously. We measure the ($p, \alpha$) $Q$ value to be 7628.8±4.9 keV. Angular distributions for the states up to 818 keV were taken and compared with distorted wave Born-approximation theory. The results of these calculations together with the proposed band structure of ${}_{}{}^{173}{}_{}{}^{}\mathrm{Tm}$ suggest possible spin assignments for our 339.8-, 526.0-, and 609.5-keV states.

NUCLEAR REACTIONS ${}_{}{}^{176}{}_{}{}^{}\mathrm{Yb}(p, \alpha )$, $E\left(p\right)=16\mathrm{}$ MeV, measured excitation energies, $Q$-value, $\sigma (\alpha , \theta )$, $\theta =15-110\mathrm{}°$, ${}_{}{}^{173}{}_{}{}^{}\mathrm{Tm}$ deduced $l$, $J$, $\pi$, enriched targets, DWBA analysis, magnetic spectrograph.

The method of dynamic nuclear orientation has been used to orient ${}_{}{}^{76}{}_{}{}^{}\mathrm{As}$ atoms present as impurities in an $n$-type silicon crystal. The measured anisotropy of the $\gamma$ rays was used to determine the orientation parameters subsequent to the 2.410 MeV $2^{-}$ → $2^{+}$ first forbidden $\beta$ transition. The $U_2$ and $U_4$ parameters characterizing the change in the orientation satisfy the relationships $\frac{U_2}{U_4}=0.95\mathrm{}\pm 0.10$ and $U_4\ge 0.30\pm 0.03$.

RADIOACTIVITY ${}_{}{}^{76}{}_{}{}^{}\mathrm{As}$; nuclear orientation, deduced angular momentum $2.410\beta$.

We investigated radiative proton capture in light nuclei in view of possible tests of meson exchange and nucleon correlation processes. We show that for proton energies between 30 and 100 MeV exchange currents are dominating the angular distributions in forward directions whereas nucleon-nucleon correlations are important mainly in backward directions. In view of possible tests of meson exchange contributions (violation of the Siegert theorem and magnetic exchange currents) precise measurements of the forward $\gamma$ production would be highly desirable.

NUCLEAR REACTIONS ($p, \gamma$), $E=30-100\mathrm{}$ MeV; calculated $\sigma$, $\sigma \left(\theta \right)$.

Formation of the 17.637 MeV state in ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ in the reaction ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ $({}_{}{}^3{}_{}{}^{}\mathrm{He}, \alpha ){}_{}{}^5{}_{}{}^{}\mathrm{Li}$ (g.s.) has been observed by an $\alpha -\alpha$ coincidence method.

NUCLEAR REACTIONS ${}_{}{}^6{}_{}{}^{}\mathrm{Li}({}_{}{}^3{}_{}{}^{}\mathrm{He}, \alpha ){}_{}{}^5{}_{}{}^{}\mathrm{Li}(\mathrm{g}.\mathrm{s}.\mathrm{})\to p+\alpha$; measured $\alpha \alpha$ coincidence as a function of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ bombarding energy, observed the formation of the ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ state.

The general structure of an exact Pauli projector is employed in the derivation of relations between Brueckner reaction matrices that are defined for a different number of occupied states (corresponding either to different nuclei or different truncations of the Pauli projector). A numerical example is given showing the truncation influence in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$.

NUCLEAR STRUCTURE Accurate methods of calculating nuclear reaction matrices.