In the present work the influence of initial excitation energy and angular momentum of the fissioning system on the angular momenta of fission fragments corresponding to ${}_{}{}^{131}{}_{}{}^{}\mathrm{Te}$ and ${}_{}{}^{133}{}_{}{}^{}\mathrm{Te}$ was studied in the ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}({\alpha }_{30\mathrm{MeV}}, f)$ system. The fragment angular momenta were estimated from the radiochemically determined independent isomeric yield ratios using a statistical model. The obtained data are discussed along with the literature data on the fragment angular momenta in the same fissioning nucleus ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ formed in the ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}(n_{\mathrm{th}}, f)$ and ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}(\alpha , f)$ systems.

NUCLEAR REACTIONS ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}({\alpha }_{30\mathrm{MeV}}, f)$ reaction, fragment angular momentum, independent isomeric yield ratio, initial excitation energy, angular momentum, single particle effect.

Fission of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ was induced by a pulsed beam of monoenergetic fast neutrons. A heavy-ion surface barrier detector was used for the detection of fission fragments. Fragment mass was determined from measured fragment energy and fragment flight time. Fragment mass distribution and correlation of fragment kinetic energy with fragment mass were obtained for neutron incident energies of 1.6, 3.1, and 5.2 MeV. A strong dependence on shell energy is suggested from the increase of the most probable total kinetic energy of the fission fragments with increase in excitation energy of the compound nucleus.

NUCLEAR REACTIONS Fission ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}(\mathrm{n}, f)$, $E_{\mathrm{n}}=1.6, 3.1, \mathrm{and} 5.2$ MeV natural target; measured fragment mass distribution and fragment kinetic energy versus fragment mass.

The fission of nuclei with $159\le A\le 232$ induced by the bombardment of 19.1 to 44.5 MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ ions has been measured using solid-state detectors with time-of-flight measurements. Analysis with statistical fission theory, including precompound nucleon emission, indicates fission barriers which decrease only slightly relative to the liquid-drop model values with decreasing $Z$, approaching about 90% of the liquid-drop model barrier for $A\approx 160$. These results are in contrast with measurements at higher angular momenta which indicate much lower fission barriers (60 to 70% of the liquid-drop model) for this mass region. The angular correlations indicate complete, or slightly greater than complete momentum transfer to the compound system. This is in opposition to that observed using heavier projectiles where incomplete momentum transfer is probable.

NUCLEAR REACTIONS, FISSION ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$, ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ta}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Re}$, ${}_{}{}^{194,195}{}_{}{}^{}\mathrm{Pt}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, ${}_{}{}^{202}{}_{}{}^{}\mathrm{Hg}$, ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$, ${}_{}{}^{206,208}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Bi}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Th}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$,f), $E\left({}_{}{}^3{}_{}{}^{}\mathrm{He}\right)=19.1\mathrm{} \mathrm{to} 44.5$ MeV; measured ${\sigma }_F(\theta , E)$, angular correlations, coincident fragment kinetic energies; deduced relative mass division, total kinetic energy release, statistical-model fission parameters.

We have measured the production of charged nuclear fragments in collisions of 1.05 GeV/nucleon and 2.1 GeV/nucleon proton, deuteron, alpha, and carbon projectiles as well as 0.4 GeV/nucleon alpha particles on targets of C, Cu, Pb, and H (from a C${\mathrm{H}}_2$—C subtraction), using a double focusing spectrometer. We present single particle inclusive cross sections for the production of $Z=1\mathrm{}$ and $Z=2\mathrm{}$ fragments in the region $0.5\le {\left(\frac{p}{Z}\right)}_{\mathrm{lab}}\le 8.7$ GV/c and $0°\le {\vartheta }_{\mathrm{lab}}\le 12°$. We discuss the relevance of the concept of limiting fragmentation to our data and point out possible uses of the data to study nuclear structure and particle production mechanisms. A detailed comparison is made with Glauber-type models and hard-scattering models as well as the coalescence model.

NUCLEAR REACTIONS $\alpha$+H, $\alpha$+C, $\alpha$+Cu, $\alpha$+Pb, $\frac{E}{A}=400\mathrm{}$ MeV/nucleon; p+H, p+C, p+Cu, p+Pb, d+H, d+C, d+Cu, d+Pb, $\alpha$+H, $\alpha$+C, $\alpha$+Cu, $\alpha$+Pb, C+H, C+C, C+Cu, C+Pb, $\frac{E}{A}=1050\mathrm{}$ MeV/nucleon; p+H, p+C, p+Cu, p+Pb, d+H, d+C, d+Cu, d+Pb, $\alpha$+H, $\alpha$+C, $\alpha$+Cu, $\alpha$+Pb, C+H, C+C, C+Cu, C+Pb, $\frac{E}{A}=2100\mathrm{}$ MeV/nucleon; measured $\sigma (\mathrm{p}, \vartheta )$ for p, d, ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^6{}_{}{}^{}\mathrm{He}$, and ${}_{}{}^8{}_{}{}^{}\mathrm{He}$.

We have measured single particle inclusive spectra of negative pions produced at angles from 0° to 12° (lab) in collisions of 1.05 and 2.1 GeV/nucleon protons, deuterons, alpha particles, and carbon nuclei with targets of C, Cu, Pb, and H (from a C${\mathrm{H}}_2$—C subtraction). Most of the pions are produced in the kinematical domains allowed in free nucleon-nucleon collisions, but for alpha and carbon projectiles we have also observed pions whose energies range up to nearly twice the kinetic energy of a nucleon in the projectile. Our results suggest that processes involving more than two colliding nucleons and/or high internal momentum components are involved in the production of these high energy pions. Comparison is made with several hypotheses of scaling including specific dynamical models, and some disagreement is observed. We present fits to the kinetic energy dependence of the data, and the target and projectile mass dependence. We also show transverse momentum distributions.

NUCLEAR REACTIONS p + H, p + C, p + Cu, p + Pb, d + H, d + C, d + Cu, d + Pb, $\alpha$ + H, $\alpha$ + C, $\alpha$ + Cu, $\alpha$ + Pb, C + H, C + C, C + Cu, C + Pb, $\frac{E}{A}=1050\mathrm{}$ MeV/nucleon; p + H, p + C, p + Cu, p + Pb, d + H, d + C, d + Cu, d + Pb, $\alpha$ + h, $\alpha$ + C, $\alpha$ + Cu, $\alpha$ + Pb, C + H, C + C, C + Cu, C + Pb, $\frac{E}{A}=2100\mathrm{}$ MeV/nucleon; measured $\sigma (p, \vartheta )$ for ${\pi }^{-}$.

Recently it has been shown that the use of a relativistic impulse approximation allows one to calculate a nucleon optical potential for use in the Dirac equation. Excellent fits have been obtained for differential cross sections and spin-dependent observables for energies greater than 400 MeV. In this work we provide a general description of the form of the momentum-space optical potential for use in the Dirac equation. It is shown that there are eight invariant functions that determine the potential. Procedures for calculating these functions are given. (In the case of nuclear matter only three of these functions are required to specify the nucleon self-energy.)

NUCLEAR REACTIONS Nucleon optical potentials for the Dirac equation; general analysis of scattering of relativistic nucleons from nuclei.

Most of the available data on the elastic scattering of pions by nuclei between 14 and 80 MeV are analyzed with a complex local optical potential which is parametrized by a bias-free Fourier-Bessel series, and is used as a means of extracting as much information from the data as possible without the explicit use of a model for the interaction. A typical shape of a negative real potential at large radii with a positive one at smaller radii is obtained and a systematic dependence on energy, charge of the pion, and isospin of the target is observed. The Kisslinger potential is shown to reproduce all these systematics, whereas the Laplacian potential fails to do so. Some results for energies of up to 230 MeV are also analyzed. The dependence of reaction cross sections on the real potential is discussed.

NUCLEAR REACTIONS Pion-nucleus "model-independent" optical potentials 14-230 MeV on various targets.

We point out that the most commonly used version of the relativistic Faddeev equations has spurious bound-state solutions and therefore it is unsuitable for calculations in the bound-state region. We propose a way to modify these equations which would correct the problem, but which leads to the loss of the clustering property. We present numerical examples for the case of the ${\pi }^{-}$ nn system.

NUCLEAR REACTIONS ${\pi }^{-}$ nn bound states; calculated Fredholm determinant $0\le \sqrt{S}\le 2018$ MeV.

A hybrid quark model for two baryons is developed. The short distance part is represented by six-quark wave functions, while the long distance part is described by conventional wave functions representing the relative motion of three-quark baryons. Formulae which give the probabilities of the six-quark configurations as a function of energy, in terms of the exterior NN interactions and experimental phase shifts, are derived and applied.

NUCLEAR REACTIONS Quark structure of nuclei, hybrid quark-baryon model of two baryons. Derivation of interior quark amplitudes from phase shifts and exterior forces. Numerical values for interior six quark probabilities for $0<E<\mathrm{}800\mathrm{}$ MeV nucleon-nucleon states.

The three body approximation of the pion-nucleus optical model is used to calculate effective strengths to be used in conventional calculations. The resulting wave functions are used to calculate pion elastic scattering and single charge exchange. It is found that observed energy shifts in elastic scattering can be understood. Considerable change in the magnitude and shape (as a function of energy) of the charge exchange cross section is a direct result of these corrections.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+}, {\pi }^{+}){}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Li}({\pi }^{+}, {\pi }^0){}_{}{}^7{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}({\pi }^{+}, {\pi }^0){}_{}{}^{13}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}({\pi }^{+}, {\pi }^0){}_{}{}^{15}{}_{}{}^{}\mathrm{O}$; calculated $\frac{d\sigma }{d\Omega \left(0\mathrm{}°\right)}$, $\sigma \left(\theta \right)$, $\sigma \mathrm{}\left(E\right)\mathrm{}$; corrections due to binding and Pauli blocking.

Data for elastic scattering of ${\pi }^{+}$ and ${\pi }^{-}$ from ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ at $T_{\pi }=162\mathrm{}$ MeV between ${\theta }_{\mathrm{lab}}=22\mathrm{}° \mathrm{and} 105°$ were analyzed by an optical model. Good fits were obtained with neutron and proton ground state densities of three-parameter Fermi shape having the same rms radius. Inelastic data for the quadrupole transitions to the ${\frac{3}{2}}^{-}$ (3.68 MeV) and ${\frac{5}{2}}^{-}$ (7.55 MeV) states and the octupole transition to a proposed ${\frac{5}{2}}^{+}$, ${\frac{7}{2}}^{+}$ doublet (11.82 MeV) were analyzed using a collective model. The extracted strengths for the neutron and proton parts of the transitions are compared to the results of electron scattering and $\gamma$-ray studies.

NUCLEAR REACTIONS ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}({\pi }^{\pm \prime }, {\pi }^{\pm })$, $T_{\pi }=162\mathrm{}$ MeV; measured $\sigma \left(\theta \right)$. Optical model and collective model analysis. $B\mathrm{}\left(\mathrm{EL}\right)\mathrm{}$ deduced.

We study threshold pion electroproduction on light $T=0\mathrm{}$ nuclei. The probe is especially interesting because it mixes longitudinal (spin component parallel to momentum transfer, $\overrightarrow{\sigma }·\overrightarrow{\mathrm{k}}$ coupling) and transverse ($\overrightarrow{\sigma }\times \overrightarrow{\mathrm{k}}$ coupling) channels. Using the local density approximation for the treatment of possible nuclear spin-isospin mode enhancements, we calculate cross sections for both exclusive and inclusive measurements. For discrete nuclear levels we study differential cross sections of various pionlike levels, and these are compared with a nonpionlike excitation. The cross sections for exclusive excitations are extremely small except for forward angles. The inclusive cross sections, achieved by summing over all nuclear states, are considerably larger since these include the quasifree excitation. All cases are studied as a function of $g^{\prime }$, the Migdal spin-isospin parameter. We find a strong influence of kinematical conditions (especially the energy transfer) and of nuclear density on enhancement phenomena.

NUCLEAR REACTIONS ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(e, e^{\prime }{\pi }^{-}){}_{}{}^{16}{}_{}{}^{}\mathrm{F}_{}^{*}{}_{}{}^{}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(e, e^{\prime }{\pi }^{-})X$; threshold pion production cross sections for exclusive and inclusive measurements; spin-isospin strength distribution effects.

We estimate the importance of rescattering diagrams involving intrinsically third-order effects in the pionic field for the process of pion absorption at rest on a pair of nucleons. The calculation is performed using a chiral bag model adapted for the correct description of higher-order pionic effects. The model provides the form factors needed in order to achieve a convergent result. The third-order diagrams cancel in part; nevertheless, the net result is as important as the conventional second-order $s$-wave rescattering mechanism for reasonable bag radii $R\sim 1$ fm and becomes dominant for bag radii $R\lesssim 0.7$ fm for internucleon distances less than about 2 fm.

NUCLEAR REACTIONS ($\pi , 2N$), pion absorption, chiral bag models.

The states of kaonic hydrogen bound by the combined Coulomb plus nuclear potentials are determined exactly in momentum space and a study is made of the dominant physics. Couplings to the $\Sigma \pi$, ${\overline{K}}^{0}n$, and $\Lambda \pi$ channels are included with different models for the strong potentials and different wave equations. The existence of both open and closed channels demands an extension of the Kwon, Tabakin, Landé treatment of the Coulomb singularity. Model studies indicate a high sensitivity to channel coupling and relativistic kinematics. The calculated $K^{-}p$ atomic shift and width agree in magnitude with recent experiments, but the theoretical shift is towards the less bound whereas the experimental shifts appear more bound.

NUCLEAR REACTIONS ($K^{-}, K^{-}$), ($K^{-}, \pi$), ($K^{-}, {\overline{K}}^0$), $E=-(0.8\mathrm{} \mathrm{keV}-20\mathrm{} \mathrm{MeV})$; $\Gamma$ hadronic atom, momentum space, coupled channels, exact Coulomb, nonlocal potentials, relativistic kinematics.

The decay of ${}_{}{}^{234}{}_{}{}^{}\mathrm{Np}$ has been investigated using a coaxial Ge(Li) detector. The source prepared by the ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$(d,3n) reaction was purified from fission products by radiochemical separation. The analysis of the $\gamma$ ray spectra revealed the presence of 59 photon lines, 29 of which were found for the first time. The absolute values of $\gamma$, EC, and ${\beta }^{+}$ intensities were deduced from Ux-$K$ ray intensity. A ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ decay scheme is suggested on the basis of the good sum relationships. Accurate values of 17 low-spin-energy levels are given, 6 of which were previously unreported in the ${}_{}{}^{234}{}_{}{}^{}\mathrm{Np}$ decay: 849.36(${03}^{-}$), 926.33(${22}^{+}$), 989.41(${22}^{-}$), 1457.1(${12}^{-}$), 1500.88(1), and 1510.22(1) keV.

RADIOACTIVITY ${}_{}{}^{234}{}_{}{}^{}\mathrm{Np}$ from ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$(d,3n); radiochemistry, Ge(Li) detector. Measured $E_{\gamma }$, $I_{\gamma }$, $I_{k-\mathrm{x}}$; deduced absolute $I_{\gamma }$, $I_{\mathrm{EC}}$, $I_{{\beta }^{+}}$, $log\mathrm{ft}$; ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ level assignment, decay scheme.

The Gamow-Teller beta-decay transitions of $\mathrm{sd}$-shell nuclei with five or more excess neutrons are calculated from complete ($0d_{\frac{5}{2}}, 1s_{\frac{1}{2}}, 0d_{\frac{3}{2}}$) space shell-model wave functions. These wave functions are obtained from diagonalizations of a model Hamiltonian formulation which reproduces observed energy-level structures throughout the $\mathrm{sd}$ shell. The calculations are carried out with both the "free-nucleon" normalization for the Gamow-Teller single-nucleon matrix elements and one based on the empirical values obtained for these quantities from a comparison of corresponding theoretical and experimental Gamow-Teller magnitudes near the line of stability. The phase-space factors $f$ which connect the reduced Gamow-Teller strengths to the total half-lives and the individual decay probabilities are calculated both from the energies obtained in the shell-model calculations and, alternatively, from hybrid energy spectra in which available experimental energies are substituted for the corresponding calculated values wherever possible. Comparisons of the beta-decay predictions to existing experimental results are presented and discussed.

RADIOACTIVITY Predictions of total half-lives and decay probabilities to individual daughter states of the isotopes of O, F, Ne, Na, Mg, Al, Si, and P which have neutron excesses of five and greater; shell-model calculations, complete $0d_{\frac{5}{2}}-1\mathrm{}{s}_{\frac{1}{2}}-0\mathrm{}{d}_{\frac{3}{2}}$ basis space, empirical $\mathrm{sd}$-shell Hamiltonian.

Shell-model calculations of the Gamow-Teller strength function for ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ have been performed utilizing a realistic finite-range two-body interaction in a model space consisting of the $2p$ and $1g$ shells. The effects of admixtures of two-particle two-hole excitations in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Nb}$, mostly due to the spin and isospin exchange components of the nucleon-nucleon force, are discussed. Ground state correlations in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ are also added via seniority-zero two-proton excitations from the $2p$ shell into the $1g_{\frac{9}{2}}$ shell. With the correlations the Gamow-Teller strength function is in good agreement with the experimental results and accounts for essentially all of the observed dispersion of strength. The inclusion of these correlations does not, however, produce either a displacement of Gamow-Teller strength to higher excitation energies, or a significant change in the total strength. Thus, they cannot account for the observed Gamow-Teller quenching. The quenching factor derived by a comparison of our calculated results with experiment is 0.52.

NUCLEAR STRUCTURE ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ calculated Gamow-Teller strength function. Analyzed contributions from two-particle two-hole admixtures in the $1g$-shell and parent ground-state correlations.

Proton and neutron single particle level spacings are determined for the $A=146\mathrm{}$ mass region, using a rotationally invariant interaction and recent experimental data. Excitation energies of spherical and deformed high spin states in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$, the transition probability $B(E2; {10}^{+}\to 8^{+})$ for several $N=82\mathrm{}$ isotones, and the $0^{+}$ excited state spectra of, and neutron pair transfer probabilities for, levels in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ are calculated. Comparisons with experimental data are made.

NUCLEAR STRUCTURE ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{148}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{150}{}_{}{}^{}\mathrm{Er}$, ${}_{}{}^{152}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Hf}$; calculated single particle spectrum, high spin yrast levels, $B\left(E2\mathrm{}\right)\mathrm{}$, $0^{+}$ excited state spectrum, pair transfer probability.

We report in this paper identification of the new isotope ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$. Uranium targets were irradiated with 28 GeV protons; after rapid retrieval of the target and separation of actinium from thorium, ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ was allowed to decay into the known ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ daughter. Exhaustive chemical purification was employed to permit the identification of ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ via its characteristic $\gamma$ radiations. The half-life derived for ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ from several experiments is 2.3±0.3 min. The production cross section for ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ is 100 μb.

RADIOACTIVITY ${}_{}{}^{233}{}_{}{}^{}\mathrm{Ac}$ produced in ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$(p, 4p2n) reaction, measured $t_{\frac{1}{2}}$ through daughter nuclide ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$. Natural uranium target, 28 GeV protons, radiochemical separation, Ge(Li) $\gamma$ spectroscopy, genetic relationship. Production cross sections of several Th and Ac isotopes.

Levels in ${}_{}{}^{196}{}_{}{}^{}\mathrm{Hg}$ have been studied by the ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}(\alpha , 4\mathrm{n})$ reaction and the high-spin level scheme of ${}_{}{}^{196}{}_{}{}^{}\mathrm{Hg}$ has been considerably extended. Backbending in both positive and negative parity yrast level sequences is discussed within the cranked shell model description.

NUCLEAR REACTIONS ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}(\alpha , 4\mathrm{n})$, $E=48.6\mathrm{}$ MeV; measured $E_{\gamma }$, $I_{\gamma }\left(\theta \right)$, $t_{\frac{1}{2}}\left(\gamma \right)$, $\gamma -\gamma$ coin; ${}_{}{}^{196}{}_{}{}^{}\mathrm{Hg}$ deduced high-spin levels, $J$, $\pi$.