We compare a proximity-type potential for two interacting nuclei with the double-folding method. Both spherical and deformed systems are considered. Special "orientation windows" are found for two deformed nuclei giving rise to nuclear cohesion. If the same nucleon-nucleon interaction is utilized, the proximity and the double-folding potentials agree fairly well for a spherical + deformed system. However, deviations are found in the case of two deformed nuclei.

The effects of large angular momenta on the fission properties of Pt isotopes are studied. Fissioning Pt systems were produced in fusion reactions of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$ and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ + ${}_{}{}^{144,150,152,154}{}_{}{}^{}\mathrm{Sm}$ in the energy range of 0.8-2.0 times the fusion barrier. The sub-barrier fusion-fission cross sections show a strong dependence on the target deformation. A pronounced increase in a simple model calculation in the total kinetic energy release with bombarding energy is accounted for by the increasing contribution of centrifugal energy. The widths of the mass and kinetic energy distributions increase rapidly with the angular momentum of the fissioning system. This effect is not accounted for by simple scission point model calculations.

[NUCLEAR REACTIONS, FISSION ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$, $E=90-148\mathrm{}$ MeV, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ + ${}_{}{}^{144,150,152,154}{}_{}{}^{}\mathrm{Sm}$, $E=180-230\mathrm{}$ MeV, measured fission cross sections, ${\sigma }_f\mathrm{}\left(E\right)\mathrm{}$, total kinetic energy and mass distributions as a function of bombarding energy. Analysis in terms of the scission point model of fission.]

Energy correlation measurements were performed for the spontaneous fission of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$, the thermal-neutron-induced fission of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$, and the photofission of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ with 12-, 15-, 20-, and 30- MeV bremsstrahlung. The photofission cross section for ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ was determined up to 30 MeV. For ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$(sf) the overall kinetic energy distribution is strongly asymmetric and the overall mass distribution has a very high peak yield (9%). Important deviations of the average total kinetic energy release $〈E_k^{*}〉$ and the average light and heavy fragment masses $〈m_L^{*}〉$ and $〈m_H^{*}〉$ from the systematics of Unik et al. are also observed for this fissioning system. These effects can be explained in the framework of the static scission point model by the strong preferential formation of a shell-stabilized scission configuration with the neutron number of the heavy and light fragments in the vicinity of the spherical $N=82\mathrm{}$ neutron shell and the deformed $N=66\mathrm{}$ neutron shell, respectively. A decrease of $〈E_k^{*}〉$ with the average excitation energy $〈E_{\mathrm{exc}}\left(E_e\right)〉$, $\frac{d〈E_k^{*}〉}{d〈E_{\mathrm{exc}}\left(E_e\right)〉}=-0.30\mathrm{}\pm 0.04$, is observed in the photofission of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$. A study of the energy-mass correlations shows that the mentioned decrease is caused predominantly by a diminution of the shell corrections in the mass region of the spherical $N=82\mathrm{}$ neutron shell. A comparison of the mass and kinetic energy distributions obtained in this work for ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$, with previously reported results for ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ and ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$ and with scission point model calculations, is also included.

[RADIOACTIVITY, FISSION ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$(sf).

NUCLEAR REACTIONS, FISSION ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}({\mathrm{n}}_{\mathrm{th}},f),{}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}(\gamma ,f),E_{{\gamma }_{max}}=12,15,20,30\mathrm{}$ MeV; measured photofission yields, fragment energies $E_1$, $E_2$; deduced $\sigma (\gamma ,f)$, $\frac{N(\mu ,E_k)}{〈E_{\mathrm{exc}}\left(E_e\right)〉}$.]

In an inclusive experiment, isotopically resolved fragments, $3\le Z\le 13$, produced in high-energy proton-nucleus collisions have been studied using a low mass time-of-flight, gas $\Delta E$-silicon $E$ spectrometer and an internal gas jet. Measurement of the kinetic energy spectra from 5 to 100 MeV enabled an accurate determination of fragment cross sections from both xenon and krypton targets. Fragment spectra showed no significant dependence on beam energy for protons between 80 and 350 GeV/c. The observed isobaric yield is given by $Y\alpha A_f^{-\tau }$, where $\tau \sim 2.6$ for both targets; this also holds for correlated fragment data. The power law is the signature for the fragment formation mechanism. We treat the formation of fragments as a liquid-gas transition at the critical point. The critical temperature $T_c$ can be determined from the fragment isotopic yields, provided one can set an energy scale for the fragment free energy. The high energy tails of the kinetic energy spectra provide evidence that the fragments originate from a common remnant system somewhat lighter than the target which disassembles simultaneously via Coulomb repulsion into a multibody final state. Fragment Coulomb energies are about $\frac{1}{10}$ of the tangent sphere values. The remnant is characterized by a parameter $T$, obtained from the high energy tails of the kinetic energy distributions. $T$ is interpreted as reflecting the Fermi momentum of a nucleon in this system. Since $T\gg T_c$, and $T$ is approximately that value expected for a cold nucleus, we conclude that the kinetic energy spectra are dominated by this nonthermal contribution.

[NUCLEAR REACTIONS $\mathrm{Xe}(\mathrm{p},X)$, $\mathrm{Kr}(\mathrm{p},X)$, $80\le E_q\le 350$ GeV; measured $\sigma (E,\theta )$, $X=\mathrm{Li} \mathrm{to} \mathrm{Al}$, $\theta ={34}^{\circ }$. Fragmentation.]

Pion charge exchange is known to be sensitive to nuclear densities. However, the extent to which different nuclear models can give different cross sections has not been carefully studied. We first demonstrate that mean field theories that give equivalent bulk properties of a given nucleus, i.e., equal charge radii and binding energies, and roughly equivalent compressibilities, symmetry energies, and removal energies, can still produce large differences in the asymptotic wave functions of the neutrons. We then show, within a distorted-wave impulse approximation reaction model, that such effects have a large influence on charge-exchange cross sections to isobaric analog and isovector monopole states. We also show to what extent the energy dependence of the O° cross section for charge exchange reflects the shape of the transition density.

Cross sections and asymmetries for quasi-elastic scattering of longitudinally polarized electrons on polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are calculated. The model used consists of impulse approximation plus closure approximation to sum over final states. At the quasi-elastic peak the asymmetry is found to be dominated by scattering from the neutron, and judicious choice of target polarization allows sensitivity to either the neutron's electric or magnetic form factor to be maximized. Away from the quasielastic peak, the protons contribute to the asymmetry. The proton's contribution is mainly owing to two partial wave channels, one mixed symmetry $S$ state and one $D$ state which have small total probability in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ wave function.

Angular distributions of the differential cross section and the analyzing power for ground state transitions in the ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^{4,5}{}_{}{}^{}\mathrm{He}$ reactions have been measured at 800 MeV using a polarized proton beam. The angular distributions of the analyzing power $A_y$ reveal a surprisingly strong spin dependence in these reactions. The analyzing power from the ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^4{}_{}{}^{}\mathrm{He}$ reaction is compared with $A_y$ data from elastic p-He scattering, the $\mathrm{pp}\to \mathrm{d}\pi$ reaction, and pion nucleon scattering, in order to find an indication of the origin to the spin dependence. Reasonably good agreement is obtained with the pion-nucleon $A_y$ data when momentum sharing is assumed between the nuclear vertices involved in a pion rescattering diagram of the ($\mathrm{p},\pi$) reaction.

[NUCLEAR REACTIONS ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^5{}_{}{}^{}\mathrm{He}$, $E_x=0\mathrm{}$ MeV, $T_{\mathrm{p}}=800\mathrm{}$ MeV; measured $\sigma (E,\theta )$, $A_y$ from ${\theta }_{\pi }^{\mathrm{c}.\mathrm{m}.\mathrm{}}=10\mathrm{}° \mathrm{to} 80°$. Comparisons with $A_y$ from ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},\mathrm{p}){}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}$, $\overrightarrow{\mathrm{p}}\mathrm{p}\to \mathrm{d}\pi$, and $\pi \overrightarrow{\mathrm{p}}$.]

Differential cross sections for elastic scattering of 80 MeV positive and negative pions from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ were measured at 5° intervals for laboratory angles from 20° to 125°. These are compared with several optical model calculations.

Angular distributions and thick-target recoil ranges have been measured for a number of products in the $A\sim 40-100$ mass range formed in the interaction of 400 GeV protons with silver. All the angular distributions peak at forward angles; the forward-backward asymmetry increases with product mass. The thick-target results were analyzed in terms of the two-step vector model. The results of both types of experiments for products with $A\gtrsim 60$ are consistent with a spallation mechanism. The results for lighter products are compared with similar data available for heavy element targets. Significant differences in the proton-nucleus interaction with respect to longitudinal momentum transfer and angular distribution are noted.

[NUCLEAR REACTIONS $\mathrm{Ag}(\mathrm{p},x)$ products ($A\sim 40-100$). $T_{\mathrm{p}}=400\mathrm{}$ GeV. Measured angular distributions, thick-target recoil ranges; off-line $\gamma$-ray spectrometry.]

We show that the $\overline{\mathrm{p}}$-atomic data for $\overline{\mathrm{p}}$+ ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, S, and ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ do not yield unique $\overline{\mathrm{p}}$-nucleus potentials. Two families of potentials are found, one with shallow imaginary and deep real parts and one with deep imaginary and shallow real parts. We examine some possible consequences for the n-$\overline{\mathrm{n}}$ oscillation time, for $\overline{\mathrm{p}}$-nuclear bound states, and for $\overline{\mathrm{p}}$-nucleus scattering.

We present an analysis of ${\pi }^{\pm }-{}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ elastic scattering by using a phenomenological ansatz for the pure hadronic amplitude; in addition a careful treatment of Coulomb effects has turned out to be essential. The resulting phase shifts and inelasticity parameters show a smooth behavior in the entire energy region between $T_{\pi }=30\mathrm{}$ and 230 MeV. The rapid increase of the differential cross sections at backward angles ($T_{\pi }=162\mathrm{}$ MeV) is discussed in terms of a semiclassical theory of the nuclear glory effect and is well reproduced by using additional information on analytic structure of the $\pi -{}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ elastic scattering amplitude in the complex $t$ plane.

[NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{\pm },{\pi }^{\pm }){}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, $E=30-226\mathrm{}$ MeV.]

The decay of ${}_{56}{}^{148}{}_{}{}^{}\mathrm{Ba}_{92}^{}{}_{}{}^{}$ to levels of odd-odd ${}_{57}{}^{148}{}_{}{}^{}\mathrm{La}_{91}^{}{}_{}{}^{}$ has been studied in experiments where $\gamma$-ray singles, time-dependent $\gamma$-ray spectra, and $\gamma \gamma t$ coincidence spectra were collected. The ${}_{}{}^{148}{}_{}{}^{}\mathrm{Ba}$ activity was produced directly by on-line mass separation. The half-life of ${}_{}{}^{148}{}_{}{}^{}\mathrm{Ba}$ was determined to be 0.61±0.03 s. A level scheme containing 26 levels and 63 $\gamma$ rays is proposed for ${}_{}{}^{148}{}_{}{}^{}\mathrm{La}$. Spin and parity for several low-lying levels are assigned on the basis of internal conversion coefficient measurements and $\beta$- and $\gamma$-ray branching. A half-life of 67±4 ns is measured for the 56-keV level. Several features of the level scheme are discussed and compared to neighboring La isotopes and $N=91\mathrm{}$ isotones.

[RADIOACTIVITY ${}_{}{}^{148}{}_{}{}^{}\mathrm{Ba}$ [from ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}({\mathrm{n}}_{\mathrm{th}},f)$] measured $E_{\gamma },I_{\gamma },{\alpha }_k,t_{\frac{1}{2}},\gamma \gamma t$ coincidence, LEPS and HpGe detectors; ${}_{}{}^{148}{}_{}{}^{}\mathrm{La}$ deduced levels, $I_{\beta },J^{\pi }$, and level halflife. Mass separated ${}_{}{}^{148}{}_{}{}^{}\mathrm{Ba}$ activity.]

The complete set of experimental results on correlations in nuclear beta decay is analyzed in terms of the general Hamiltonian including scalar, vector, axial vector, and tensor interactions with an arbitrary degree of parity violation. It is concluded that the standard vector minus axial-vector model with maximal parity violation (left-handed lepton current) is compatible with the data and rigorous limits are obtained for the values of possible additional coupling constants. In the scalar and tensor case the new constraints are considerably tighter than those published before: $\left|\frac{C_S}{C_V}\right|$ and $\left|\frac{C_S^{\prime }}{C_V}\right|\le 0.2$, $\left|\right(\frac{C_S+C_S^{\prime })}{C_V}|\le 0.06$; $\left|\frac{C_T}{C_A}\right|$ and $\left|\frac{C_T^{\prime }}{C_A}\right|\le 0.09$, $\left|\right(\frac{C_T+C_T^{\prime })}{C_A}|\le 0.01$, all at the 95% confidence level. On the other hand, rather large admixtures of the right-handed lepton currents ($\frac{C_V^{\prime }}{C_V}\ne 1$ or $\frac{C_A^{\prime }}{C_A}\ne 1$) are allowed by the data. An analysis of the correlations between various coupling constants implied by the data is also performed.

[RADIOACTIVITY Correlations in $\beta$ decay analyzed; limits on unusual couplings deduced.]

Gamma rays and conversion electrons were measured for the ${}_{}{}^{244}{}_{}{}^{}\mathrm{Am}$ beta decay isomers in an ${}_{}{}^{243}{}_{}{}^{}\mathrm{Am}$ target undergoing neutron capture in a high-flux reactor. New transitions accompanying beta decay of 26-min ${}_{}{}^{244}{}_{}{}^{}\mathrm{Am}_{}^g{}_{}{}^{}$ were observed. These include 984.92-keV and 977.80-keV $E0\mathrm{}$ transitions assigned to the deexcitation of a first-excited $0^{+}$ band in ${}_{}{}^{244}{}_{}{}^{}\mathrm{Cm}$ with level energies of 984.91 ($0^{+}$) and 1020.76 ($2^{+}$) keV. The ratio of reduced transition probabilities $\frac{B\left(E0\mathrm{}\right)\mathrm{}}{B\left(E2\mathrm{}\right)\mathrm{}}$ for the $0^{+}$ level is 1.5±0.2.

Although a great deal of experimental work has succeeded in limiting a possible second class axial coupling to about ten percent of the size of weak magnetism, published limits on the size of a possible second class polar vector current are one order of magnitude less sensitive. We summarize the present situation and demonstrate that muon capture provides the strictest present limit.

We apply the symplectic shell model to the breathing mode in closed-shell nuclei. The group theory of $\mathrm{Sp}\mathrm{}(2,R)\mathrm{}$ is used to embed the description of the collective monopole excitation in the framework of the oscillator shell model. This provides a microscopic description of the breathing mode by way of a diagonalization of the effective interaction in an appropriate collective subspace. We apply this model to closed-shell nuclei ranging from ${}_{}{}^{56}{}_{}{}^{}\mathrm{Ni}$ to ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ using various Skyrme-type forces. The results confirm that a force with a nuclear matter incompressibility of about 200 MeV reproduces the experimental breathing mode energies. An evaluation of the calculated wave functions using the formalism of the $\mathrm{Sp}\mathrm{}(2,R)\mathrm{}$ boson picture indicates the importance of two-boson correlations that particularly affect the compression modulus. As an element in our analysis we compare $\mathrm{Sp}\mathrm{}(2,R)\mathrm{}$ model and random phase approximation results. This reveals the strengths and limitations of the symplectic model.

[NUCLEAR STRUCTURE $\mathrm{Sp}\mathrm{}(2,R)\mathrm{}$ symplectic shell model applied to breathing mode in medium and heavy closed shell nuclei.]

The strength distribution of the $2^{-}$ states in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ is calculated including the $\Delta$-isobar quenching effects. The theoretical $B \mathrm{}\left(M2\mathrm{}\right)\mathrm{}$ values up to 8 MeV are dominated by the orbital angular momentum part of the $M2\mathrm{}$ operator. Therefore we find only little quenching in this energy region owing to the $\Delta$-particle nucleon-hole admixtures.

[NUCLEAR STRUCTURE ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$; $\Delta$-isobar effects on $M2\mathrm{}$ strength.]

It is shown that the Nilsson prescription for calculating equilibrium deformations of nuclei under the constraint of constant volume may be interpreted in terms of a Hartree mean-field approximation applied to nucleons interacting via many-body forces. Such an interaction is obtained in closed form, having a Taylor expansion beginning with the familiar quadrupole-quadrupole interaction, and then successively adding three-body, four-body, etc., terms. Since the interaction is not uniquely determined, two interesting forms are discussed. One, having both monopole and quadrupole parts, has a Hartree field identical to the Nilsson potential. The other, which is purely quadrupole, permits a generalization to all orders of a result obtained by Moszkowski for small deformations. The scalar many-body interaction naturally explains the nonscalar effective two-body interactions used in random-phase approximation calculations of deformed nuclei.

Renormalized single-particle matrix elements of the magnetic dipole moment operator for the (${2p}_{\frac{3}{2}}$, ${1f}_{\frac{5}{2}}$, ${2p}_{\frac{1}{2}}$) space are calculated in the framework of perturbation theory involving first- and second-order excitations from the ${1f}_{\frac{7}{2}}$ core. The calculated dipole matrix elements are consistent with the empirical values deduced from the observed $M1\mathrm{}$ transitions as well as dipole moments in several Ni and Cu isotopes.

[NUCLEAR STRUCTURE Renormalized magnetic dipole moment operator; restricted valence space spanned by the ${2p}_{\frac{3}{2}}$, ${1f}_{\frac{5}{2}}$, and ${2p}_{\frac{1}{2}}$ orbits; first- and second-order diagrams; empirical values of the effective $M1\mathrm{}$ single-particle matrix elements.]

The transverse ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(e,e′) inelastic spectrum has been measured at 180° up to an excitation energy of 96 MeV for 150.6 MeV incident electrons. This spectrum is compared to a recent self-consistent random phase approximation calculation which includes multipolarities of $J\le 3$. The calculated cross section is larger than the experimental cross section in the quasielastic peak region, and resonance states are predicted in the 20-35 MeV region which are not observed.

[NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(e,e′); $E=150.6\mathrm{}$ MeV, $\theta =180\mathrm{}°$; measured $\sigma (E,\theta )$.]