The neutron capture cross sections and solar abundances of ${}_{}{}^{160,161}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{170,171}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{175,176}{}_{}{}^{}\mathrm{Lu}$, and ${}_{}{}^{176,177}{}_{}{}^{}\mathrm{Hf}$ have been measured. With this data base $s$-process studies have been carried out to determine the $s$-process neutron density and temperature and to investigate the $s$-process nucleosynthesis of the ${}_{}{}^{176}{}_{}{}^{}\mathrm{Lu}$ clock. From various branchings the neutron density was found to be (0.8-1.8)×${10}^8$ neutrons per ${\mathrm{cm}}^3$ and the temperature $\mathrm{kT}$ to be 18—28 keV. On the basis of the present data, ${}_{}{}^{176}{}_{}{}^{}\mathrm{Lu}$ proved not to be applicable as a cosmic clock because of the temperature sensitivity of the ${}_{}{}^{176}{}_{}{}^{}\mathrm{Lu}$ half-life but can be used instead as a stellar thermometer. Constraints for the $s$-process temperature ($kT=20-28\mathrm{}$ keV) were found to be in good agreement with the investigated branchings.

The physical idea behind the present approach is that the ($a$,$\mathrm{ab}$) reaction continuum consists mainly of those particles $a$,$b$, following a quasifree knockout collision, which undergo an energy degradation due to rescattering on their way out from the target nucleus. The Feshbach, Kerman, and Koonin statistical two-body theory of the ($a$,$b$) reaction continuum is then extended to also describe this exclusive continuum process. A computable expression for the direct ($a$,$\mathrm{ab}$) continuum cross section is deduced as a convolution integral over a doorway quasifree cross section and a number of factors describing the probability of multiple rescattering of the quasifree particles on the residual nucleus. The resemblance between the two-body and the three-body expressions is remarkable and reflects their common physical support.

Fragments of the $g_{\frac{9}{2}}$ isobaric analog states in ${}_{}{}^{51}{}_{}{}^{}\mathrm{Mn}$ corresponding to $E_x=4.101\mathrm{}$ MeV ($S_n=0.10\mathrm{}$) and $E_x=4.155\mathrm{}$ MeV ($S_n=0.34\mathrm{}$) parent states in ${}_{}{}^{51}{}_{}{}^{}\mathrm{Cr}$ have been found. To locate the $g_{\frac{9}{2}}$ isobaric analog resonance fragments the ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}(\mathrm{p},{\mathrm{p}}_1\gamma )$, ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}(\mathrm{p},{\mathrm{p}}_2\gamma )$, and ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}(\mathrm{p},\gamma ){}_{}{}^{51}{}_{}{}^{}\mathrm{Mn}$ reactions were used. The excitation curves were measured in the $E_{\mathrm{p}}=3.08-3.36\mathrm{}$ MeV proton energy range. The excitation function of the (p,${\mathrm{p}}_2\gamma$) reaction turned out to be a sensitive tool to locate resonances with higher, $\frac{5}{2}\le J_R\le \frac{13}{2}$, spins. The spins of the resonances were found using the method of normalized angular distributions. Fifteen $g_{\frac{9}{2}}$ fragments were identified. Partial widths for each fragment and in all three channels were deduced and fine structure analyses were carried out. Inelastic spectroscopic factors and Coulomb displacement energies were derived for both fragmented $g_{\frac{9}{2}}$ isobaric analog resonances. The results were compared with previous work.

The reaction ${}_{}{}^{41}{}_{}{}^{}\mathrm{K}$(t,p)${}_{}{}^{43}{}_{}{}^{}\mathrm{K}$ has been investigated with a 15-MeV triton beam. Twenty levels of ${}_{}{}^{43}{}_{}{}^{}\mathrm{K}$ (many of them unreported previously) have been identified up to about 3.4 MeV excitation energy. Angular distributions were measured for all levels. Comparison with distorted-wave Born-approximation calculations allows extraction of $L$ values for most of them. Three multiplets arising from the couplings of ${\left(1\mathrm{}{f}_{\frac{7}{2}}\right)}_{J=2\mathrm{}}^2$ and ${\left(1\mathrm{}{f}_{\frac{7}{2}}\right)}_{J=4\mathrm{}}^2$ transferred neutrons with the $1d_{\frac{3}{2}}$ proton hole have been identified in ${}_{}{}^{43}{}_{}{}^{}\mathrm{K}$. Their energy centroids are closely related to the ${\left(1\mathrm{}{f}_{\frac{7}{2}}\right)}^4$ spectrum of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$. The general sum rules for two-nucleon transfer reactions and a more specialized sum rule give a good account of the data and suggest spin and parity assignments for many of the observed states. The positive parity states in ${}_{}{}^{43}{}_{}{}^{}\mathrm{K}$ are compared with $f_{\frac{7}{2}}^4{\left(d_{\frac{3}{2}}{s}_{\frac{1}{2}}\right)}^{-1\mathrm{}}$ and $f_{\frac{7}{2}}^3{p}_{\frac{3}{2}}{d}_{\frac{3}{2}}^{-1\mathrm{}}$ shell-model calculations.

Important breakings of the multi-$j$ $\mathrm{U}\left(\frac{6}{12}\right)$ supersymmetry schemes have been observed in the ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$(d,p)${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}$ reaction. Including only in the analysis the known levels with $J<\mathrm{}4\mathrm{}$ below 1.5 MeV excitation energy, it appears that an appreciable fraction, 36%, of the total observed strength corresponds to transitions to the $2_2^{+}$, $0_2^{+}$, and $0_3^{+}$ levels, forbidden in the $\mathrm{U}\left(\frac{6}{12}\right)$ scheme but experimentally observed with 19%, 21%, and 36% of the strength of the allowed transition to the ground state.

Inclusive cross sections for energetic protons emitted at backward angles were measured using a 200 MeV proton beam bombarding ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$,${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ targets. The data were analyzed using the quasi-two-body scaling approach. It is shown that a scaling regime is reached for some of the data taken at incident energies of about 200 MeV/nucleon. This regime, however, is different from the one observed above 600 MeV/nucleon.

The ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$,p) reaction, at a bombarding energy of 39.0 MeV, has been used to locate candidates for high-spin states. Angular distributions and angle-integrated cross sections are presented for 43 levels (or groups of levels) of which at least 10 probably have $J\ge \frac{9}{2}$.

The ${}_{}{}^6{}_{}{}^{}\mathrm{Li}+{}_{}{}^6{}_{}{}^{}\mathrm{Li}\to 3\alpha$ reaction has been studied in a kinematically complete experiment at 2.4 and 4.2 MeV incident energy. Information on the behavior of quasifree effects around the Coulomb barrier is discussed.

In elastic scattering between $4N$ nuclei, a rising oscillatory structure often appears in the differential cross section at backward angles. This anomalous phenomenon is explained by an $\alpha$ transfer process between the nuclei. For ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ scattering ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ is considered to be composed of an ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ core with two alpha particles orbiting around it. These valence particles may be transferred between the cores during the scattering. The nuclear molecular orbital model is applied. A natural agreement with the experimental data can be reached without any adjustment of the parameters involved.

In a systematic study of strongly damped reaction mechanisms between medium mass nuclei we have measured the evaporation residue and the fissionlike fragments from the ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$+${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ reaction. The mass and angular distributions and the total kinetic energies for fissionlike fragments were measured. A strong angular dependence of the mass distribution has been observed. The cross sections for the production of fusion evaporation and fissionlike fragments have been determined and the fusion cross section deduced. The latter were compared to various fusion model predictions including those developed to describe the so-called fast fission and quasifission. The results are interpreted in terms of a process which we call dynamical fission, the basic concepts of which are consistent with those of the extra push model and those of the fast fission model in the subcritical mass transfer regime.

High spin states have been studied in ${}_{}{}^{78}{}_{}{}^{}\mathrm{Rb}$ using the ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$(${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$,3pn)${}_{}{}^{78}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}({}_{}{}^{28}{}_{}{}^{}\mathrm{Si},\alpha \mathrm{pn}){}_{}{}^{78}{}_{}{}^{}\mathrm{Rb}$ reactions at laboratory energies of 103.5 and 108 MeV. $\gamma -\gamma$ coincidence and $\gamma$-ray angular distribution measurements were performed. New states were found at 1511[${10}^{\mathrm{}(-)\mathrm{}}$], 1908[${11}^{\mathrm{}(-)\mathrm{}}$], 2929[${13}^{\mathrm{}(-)\mathrm{}}$], 4143[(${15}^{-}$)], and 1004[$8^{\mathrm{}(-)\mathrm{}}$] keV above the bandhead state. The latter state is probably the $4^{\mathrm{}(-)\mathrm{}}$, 5.74 min isomeric state whose excitation energy lies somewhat above 103 keV. The states populated in this reaction group into two decay sequences which appear to be rotational bands. The moment-of-inertia parameter $\frac{{\hslash }^2}{2\mathcal{I}}$ is about 20 keV. There is a close similarity to the level structure of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Br}$.

An excitation function for the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{18}{}_{}{}^{}\mathrm{O},\alpha ){}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ was measured at $\vartheta =7\mathrm{}°$ (lab) in the energy range 10-15 MeV (c.m.). Resonancelike structures are observed for the ground state at $E=11.5, 12.8, \mathrm{and} 14.3$ MeV (c.m.). For the summed group of states $E_x=0.00-5.71\mathrm{}$ MeV, structures are correlated with the ground-state excitation function and, to some extent, with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$($2^{+}$))${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ inelastic-scattering data. Angular distributions have been measured in the energy range $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=10.8-12.2\mathrm{}$ MeV. An angular distribution for the ground state at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=11.6\mathrm{}$ MeV is dominated by $l=10\mathrm{}$. Legendre polynomial expansion coefficients for $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=10.8-12.2\mathrm{}$ MeV are presented.

The fission of ${}_{}{}^{255,256}{}_{}{}^{}\mathrm{Es}$, ${}_{}{}^{255-257}{}_{}{}^{}\mathrm{Fm}$, and ${}_{}{}^{258}{}_{}{}^{}\mathrm{Md}$ has been studied in the excitation energy range from threshold to 25 MeV. A target of ${}_{}{}^{254}{}_{}{}^{}\mathrm{Es}$ was used in the direct reaction studies; (d,$\mathrm{p}f$), (t,$\mathrm{p}f$), (${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$\mathrm{d}f$), (${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$\mathrm{p}f$), and in the compound induced fission reactions formed with p, d, t, and $\alpha$ particle projectiles. Coincident fission fragment energies were recorded along with (in the direct reaction studies) the outgoing light charged particle. The mass and kinetic energy distributions were studied as a function of nuclear excitation energy. The observed bulk properties were consistent with established systematics in that they exhibited an asymmetric mass distribution and a phenomenologically consistent total kinetic energy. However, the systems demonstrated a fission decay mode which we ascribe to high energy symmetric fission decay. This component, though somewhat arbitrary in its definition, showed a general decrease in yield as a function of increasing nuclear excitation energy. This observed rapid change in fission properties between "normal" and high energy symmetric fission probably points to the important observable consequences that can occur from small variations in the potential energy surface.

The differential cross section for n-p elastic scattering at 801.9 MeV has been measured with high statistical precision and good relative accuracy over the angular range $60°<{\theta }^{*}<180\mathrm{}°$. The absolute normalization is based on the simultaneously observed yield of deuterons from the $\mathrm{np}\to \mathrm{d}{\pi }^0$ reaction and is good to 7%. A nearly monoenergetic neutron beam, produced by proton bombardment of a liquid-deuterium target, was directed through a liquid-hydrogen target. The angle, velocity, and momentum of charged particles ejected from the target were measured in a magnetic spectrometer equipped with multiwire proportional chambers and timing scintillators. The results are in good agreement with earlier Saclay and LAMPF data and include an angular region not covered before. The pole-extrapolation method of Chew was used to extract a value $f^2=0.075\mathrm{}\pm 0.005$ for the pion-nucleon coupling constant which is in agreement with accepted values, thus providing evidence for the accuracy of the shape and normalization of the angular distribution.

The angular distributions of the differential cross sections and analyzing powers are presented for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\mathrm{p},{\pi }^{+}){}_{}{}^{13}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}$ reaction leading to the ground state of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ as well as some of the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}$ low-lying excited states. The analyzing powers for some of the transitions exhibit a considerable energy dependence while for other transitions they remain relatively unchanged, thus indicating a dynamic sensitivity of the analyzing power dependent on nuclear structure. Comparisons of theoretical predictions for $A_{N0\mathrm{}}$ and $\frac{d\sigma }{d\Omega }$, based on microscopic two-nucleon models, with our results indicate that substantial differences between theory and experiment still exist for $A(\mathrm{p},{\pi }^{+})A+1\mathrm{}$ type of reactions.

A new approximation method for potential scattering is proposed. The usual idea of linearizing propagators in eikonal approximation is incorporated with the second Born approximation in this method such that the scattering amplitude retains more accurate low order Born terms. Consequently, the linearized propagator is dependent on the specifics of the potential. The new formula thus obtained gives spectacular improvements to usual eikonal formulas. Interestingly it works also for scatterings at not so high energy.

The neutron pickup reaction (p,d) has been studied at a proton energy of 800 MeV on targets of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. States known to correspond to single-hole excitations are seen and in most cases the data are properly understood through distorted-wave Born approximation calculations. High-spin final states are prominent, and some are shown to be excited through multiple step processes. The strongest states seen in the data do not correspond to known levels.

A (p,2p) experiment was carried out at 2.1 GeV to search for interactions between the incident proton and a fast dinucleon constituent inside the target nucleus. The results of this experiment along with a Two-Armed Spectrometer System used to make these coincidence measurements are described. Data are presented that indicate a possible contribution to the backscattered proton spectrum from such a dinucleon structure, although effects of statistics and experimental resolution allow only an upper limit to be set on the magnitude of this contribution. Effects of phase space, Fermi motion, and final state interactions on these measurements are discussed. A comparison with an intranuclear cascade model is shown. The systematics of other two-particle coincidence spectra obtained in this experiment are also presented.

In a recent paper, a calculation of the self-consistent $\pi \mathrm{N} t$ matrix in nuclear matter was presented. In this calculation the driving term of the self-consistent equation was chosen to be a static approximation to the free $\pi \mathrm{N} t$ matrix. In the present work, the earlier calculation is extended by using a nonstatic, fully-off-shell free $\pi \mathrm{N} t$ matrix as a starting point. Right-hand pole and cut contributions to the $P$-wave $\pi \mathrm{N}$ amplitudes are derived using a Low expansion and include effects due to recoil of the interacting $\pi \mathrm{N}$ system as well as the transformation from the $\pi \mathrm{N}$ c.m. frame to the nuclear rest frame. The self-consistent $t$-matrix equation is rewritten as two integral equations which modify the pole and cut contributions to the $t$ matrix separately. The self-consistent $\pi \mathrm{N} t$ matrix is calculated in nuclear matter and a nonlocal optical potential is constructed from it. The resonant contribution to the optical potential is found to be broadened by 20% to 50% depending on pion momentum and is shifted upward in energy by approximately 10 MeV in comparison to the first-order optical potential. Modifications to the nucleon pole contribution are found to be negligible.

We have measured the cross section of the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+},{\pi }^{+}\mathrm{p}){}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ in the region of the ${\Delta }^{++}$ resonance to determine whether the width or central energy of the resonance are modified if $\pi$,p scattering takes place inside a nucleus. No significant changes were found within the accuracy of our experiment.