Nuclear deformation of the $s-d$ shell nuclei ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ has been investigated by means of fast neutron scattering. Differential cross sections have been measured at the incident neutron energies of 9.76 and 14.83 MeV, over the angular range from 15° to 160°. Angular distributions have been obtained for the elastic scattering and the inelastic scattering to low lying collective states. The measurements have been compared to the predictions of collective models, and nuclear deformations have been determined for these nuclei. The coupled-channel and compound-nucleus formalisms were used in the calculations. The analysis shows that these nuclei exhibit quite different shapes, and confirms the oblate deformation of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ established in recent works. A detailed comparison of the deformations obtained in this study with those deduced from (p,p′), (d,d′), ($\alpha$,${\alpha }^{\prime }$), (${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}\prime$), other (n,n′), and charge distribution measurements is presented and discussed. It is emphasized that for these $N=Z$ nuclei the quadrupole deformations and deformation lengths are in very good agreement when measured through neutron and proton scattering as well as electromagnetic excitations.

Angular distributions of the analyzing power $A_y\left(\theta \right)$ for the elastic n-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ scattering have been measured in the energy range 15-50 MeV. A continuous energy polarized neutron beam was produced using a 52 MeV polarized deuteron beam incident on a liquid deuterium target. A liquid helium scintillation detector was used as a scattering sample. Scattered neutrons were detected with 14 scintillation detectors. Multiparameter data acquisition was performed to discriminate against background events. The incident neutron energy was determined off line by cuts in the incident time-of-flight spectra. The data were normalized in the backward angle maxima by previous N-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ data. The results were used as input in a series of phase shift analyses. Coulomb correction procedures to p-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ phase shifts have been used to provide n-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ predictions. The validity of these procedures has been tested. A set of n-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ phase shifts, varying smoothly with energy, is given which reproduces the new data very well.

A separable representation of the Paris potential is constructed by means of the Ernst-Shakin-Thaler method. The resulting separable interactions represent a good approximation of the on-shell as well as off-shell properties of the Paris potential. Their form factors are composed of rational functions not too complicated for today's computer codes for few-body systems. The various features of the nucleon-nucleon force are discussed together with first results obtained with these separable potentials for elastic electron-deuteron and nucleon-deuteron scattering.

A high precision study of the ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}(\mathrm{n},\gamma ){}_{}{}^{166}{}_{}{}^{}\mathrm{Ho}$ reaction, analyzed with advanced signal processing methods, has revealed the presence of 270 transitions with photon energy greater than 4050 keV. Application of a statistical model suggests that these transitions are most likely primary in nature and hence directly reflect the levels in ${}_{}{}^{166}{}_{}{}^{}\mathrm{Ho}$ up to an excitation above 2 MeV. The present data substantiate much of the level energy data below 1 MeV previously reported but, in most instances, with marked improvement in precision. In addition, new information on the previously unexplored region above this energy is presented. The level energies deduced from the high energy measurements have been refined, when possible, through use of crystal spectrometer data. The neutron separation energy is found to be 6243.68(2) keV. When the density of levels in ${}_{}{}^{166}{}_{}{}^{}\mathrm{Ho}$ is treated using a statistical model in which this quantity is represented by a constant temperature, the value for this parameter is found to be 520 keV.

The (t,${}_{}{}^3{}_{}{}^{}\mathrm{He}$) charge exchange reaction has been used to locate Gamow-Teller states with $T_0+1\mathrm{}$ isospin in the region of $A=54-58\mathrm{}$. These data were obtained at $E_{\mathrm{t}}=25\mathrm{}$ MeV on targets of ${}_{}{}^{54,56,58}{}_{}{}^{}\mathrm{Fe}$ and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$.

The bremsstrahlung cross section has been studied by measuring the activity induced in ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ by electrodisintegration and when thin radiators of Cu, Mo, Ta, and Th were placed in the electron beam just ahead of the target. The electron energies were varied from 13.5 to 60 MeV for the electrodisintegration and from 20 to 60 MeV for the radiator-in measurements; the ($\gamma$,n) cross section for ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ was determined using virtual photon theory; the radiator data were fitted using various bremsstrahlung cross sections. The best fit is obtained using the synthesized spectrum of Seltzer which differs from the Davies-Bethe-Maximon cross section as given by equation (3CS) of Koch and Motz.

The microscopic nonrelativistic first-order optical potential for proton-nucleus scattering is studied in some detail. Momentum-space calculations have been performed for a number of different target nuclei at proton energies above ∼100 MeV and these microscopic predictions are compared with experimental cross section, analyzing power, and spin-rotation function data. The input to these calculations consists of the free on-shell nucleon-nucleon $t$ matrix, its nonlocal and off-shell structure, the treatment of the full-folding integral, and target densities obtained from electron scattering. Off-shell and nonlocal effects, as well as various factorization approximations, are studied. The sensitivity to uncertainties in the off-shell extension of the $t$ matrix, within the context of the Love-Franey model, is explicity displayed. Similarly, uncertainties due to nonlocalities and incomplete knowledge of nuclear densities are shown. Explicit calculations using the $t$ matrix of Love and Franey indicate that these effects play significant roles only for relatively large angles ($\theta \lesssim 60°$) and/or lower energies (∼150 MeV). These studies reinforce the conclusion that the lack of agreement between such first-order predictions and the data for spin observables at small angles arises from a physical effect not included in the nonrelativistic first-order theory, rather than from any uncertainty in the calculation or in its input.

The neutron total cross sections of ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$ and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Cr}$ have been measured in the energy range from a few tens of keV to about 900 keV using a neutron time-of-flight technique and a pulsed electron linear accelerator. The nominal resolution of the measurements was about 0.06 ns/m. The total cross-section data have been analyzed using an $R$-matrix multilevel multichannel code to determine values of the resonance parameters ($E_0$, $g{\Gamma }_{\mathrm{n}}$, and $J^{\pi }$) and to investigate the parity dependence of the level densities of ${}_{}{}^{53}{}_{}{}^{}\mathrm{Cr}$ and ${}_{}{}^{55}{}_{}{}^{}\mathrm{Cr}$ at high excitation. From these analyses we obtain the following values for the average properties of the resonance parameters for $s$-wave resonances up to about 900 keV and for $p$-wave resonances up to 600 keV: $D_0=(45\mathrm{}\pm 6)$ keV, $S_0(\times {10}^4)=(3.0\mathrm{}\pm 1.0)$, $D_1=(8.5\mathrm{}\pm 0.6)$ keV, $S_1(\times {10}^4)=(0.70\mathrm{}\pm 0.12)$ for ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$; and $D_0=(60\mathrm{}\pm 9)$ keV, $S_0(\times {10}^4)=(2.6\mathrm{}\pm 0.9)$, $D_1=(9.2\mathrm{}\pm 0.5)$ keV, $S_1(\times {10}^4)=(0.67\mathrm{}\pm 0.11)$ for ${}_{}{}^{54}{}_{}{}^{}\mathrm{Cr}$. The distributions of reduced neutron widths for $s$- and $p$-wave resonances for each isotope show good agreement with the Porter-Thomas distribution. The values of the ${\Delta }_3$ statistic for the long-range correlation of $s$-wave resonances for both ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$ and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Cr}$ and found to be in reasonable agreement with the theoretical prediction of Dyson and Metha. The values for the ratio $\frac{D_0}{D_1}$ for both nuclides are larger than expected from a ($2J+1$) level dependence, indicative of a parity dependence of the level densities of ${}_{}{}^{53}{}_{}{}^{}\mathrm{Cr}$ and ${}_{}{}^{55}{}_{}{}^{}\mathrm{Cr}$ at high excitation.

Three methods for calculating the breakup-fusion cross sections are compared; ours, and those of Baur and Trautmann and of Kasano and Ichimura. All three use the two-step and the spectator approximations. It will be shown first that, while ours does not make any further approximation, the other two make a few additional approximations. Errors caused by these additional approximations are assessed numerically. The errors are found rather large in general. A critical assessment of the formalism by Austern and Vincent, on which the work of Kasano and Ichimura was based, is also made.

In an earlier work it was assumed that the imaginary part of the optical potential due to nucleon transfer could be described by a proximity-type formula. Here we derive such a formula starting from the transfer probabilities between specific quantum states and assuming leptodermous nuclei.

Energy spectra of complex nuclei ($Z_f=5-10\mathrm{}$) emitted in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ collisions at $\frac{E}{A}=30\mathrm{}$ MeV were measured at angles significantly larger than the grazing angle. The angular dependence of these energy spectra gives clear evidence for the emission of these complex fragments prior to the attainment of statistical equilibrium of the compound nucleus. The qualitative features of the data are rather well described by assuming that complex fragments are emitted from a localized region of high excitation which is in the process of equilibration with the surrounding cold nuclear matter or, alternatively, that the target nucleus is shattered into several fragments by the incoming projectile.

The ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({}_{}{}^7{}_{}{}^{}\mathrm{Li},\alpha ){}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ reaction has been investigated at an incident energy of 20 MeV. Complete angular distributions were measured in the angular range ${\theta }_{\mathrm{lab}}=7.5\mathrm{}°-157.5\mathrm{}°$ using a multiangle spectrograph. Known ${\mathrm{}\left(\mathrm{sd}\right)\mathrm{}}^3$ states are populated about twice as strongly as the core-excited four-particle—one-hole (4p-1h) states. Angular distributions for members of the ground-state band show only a moderate forward-angle rise, and those of the negative-parity band and other weak states are approximately symmetric around 90°. Results have been analyzed in terms of Hauser-Feshbach compound-nucleus calculations and finite-range distorted-wave Born approximation calculations in which the three transferred nucleons enter the $\mathrm{sd}$ and/or $1p$ shells. The contribution of the compound-nucleus cross section has been estimated. The data for the $K^{\pi }={\frac{1}{2}}^{+}$ and $K^{\pi }={\frac{1}{2}}^{-}$ bands in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ could be well fitted by an incoherent sum of direct and compound reaction cross sections. Simple analysis of the integrated cross sections based on a ($2J+1$) rule is consistent with results of the Hauser-Feshbach calculations. Comparison between the present experimental results and previous triton cluster transfer reactions on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ emphasizes the enhanced compound/direct ratio for the 4p-1h and other weak states in the present data.

A time-dependent mean-field theory is developed for fast nucleon emission in nuclear heavy-ion reactions. The essence of the model is to treat the relative motion of the ions classically while treating the internal excitations quantum mechanically. General properties of the model are calculated by assuming a phenomenological external field. The model is applied to study fast neutron emission from the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$.

We explore the possibility that the process of a three-fragment breakup observed in the reactions of ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$ and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ on ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at about 11 MeV per nucleon may arise from an intermediate rotating toroidal nucleus with $l\sim 130$. Quantitative characteristics of the toroidal nuclei are presented.

The atomic charge state distributions of ${}_{}{}^{154-158}{}_{}{}^{}\mathrm{Er}$ ions produced in fusion reactions with ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$ beams and ${}_{}{}^{126-130}{}_{}{}^{}\mathrm{Te}$ targets are used to deduce the average internal conversion probabilities of continuum $\gamma$ transitions at high spin. A strong dependence is observed on both neutron number and spin. For each of the nuclei ${}_{}{}^{155-158}{}_{}{}^{}\mathrm{Er}$ a critical spin is observed at which a sudden enhancement of internal conversion occurs. This result alone implies either a sudden enhancement of $M1\mathrm{}$ radiation, a sudden decrease of the average $E2\mathrm{}$ transition energy, or some mixture of the two. In either case a major change in the underlying structure of the rotating body is implied. Previous continuum $\gamma$-ray spectroscopy measurements support the interpretation involving enhanced $M1\mathrm{}$ radiation at very high spin.

A general reaction theory of the heavy-ion fusion cross section that clearly exhibits the possible effects of directly coupled channels is developed. Our expression for the fusion cross section shows how the presence of coupled channels enhances its value in general. The result may be used to standardize the discussion of, e.g., sub-barrier heavy-ion fusion in general.

The fractions of tin fission products formed independently and by decay of indium isotopes were determined for $A=121, 123, 125, 127, \mathrm{and} 128$ from thermal-neutron-induced fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, and for $A=121, 123, 127, \mathrm{and} 128$ from 14-MeV-neutron-induced fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. The procedure involved on-line chemical separation of indium and tin fission products by use of a continuous-extraction method during irradiation and beta-activity measurements of purified tin samples after decay of indium precursors. Measured fractions of tin isotopes formed directly or by beta decay combined with their cumulative yields and mass-number (chain) yields allowed calculation of independent and/or cumulative yields for the nuclides studied. The yields of indium isotopes agree with complementary technetium yields measured radiochemically, but they are lower than most indium yields measured mass spectrometrically and most complementary technetium yields measured with recoil separators. The yield data were used to determine mass- and charge-distribution parameters ${\sigma }_{A^{\prime }}$, $\Delta A^{\prime }$, $Y\left(Z\right)\mathrm{}$, ${\sigma }_Z$, and $\Delta Z$ for thermal-neutron-induced fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. The values of ${\sigma }_{A^{\prime }}$ and ${\sigma }_Z$ are similar to the averages of values derived for other elements and mass numbers. $\Delta A^{\prime }$ has a pronounced peak at $Z=50\mathrm{}$, and the elemental yield decreases sharply from $Y(Z=50\mathrm{})=4.0\%$ to $Y(Z=49\mathrm{})=0.1\%$. The $\Delta Z$ function increases abruptly near $Z=50\mathrm{}$, changing from ∼-0.45 to positive values, as indicated by earlier experimental data, but inconsistent with the scission-point theoretical predictions. These effects, associated with the fifty-proton shell, diminish at higher excitation energy.

Proton inelastic cross sections have been measured for the $5^{-}$ and $6^{-}$ ($T=0, 1$) states of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ and the $6^{+}$ state of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ at $E_{\mathrm{p}}=333, 498, \mathrm{and} 800$ MeV. These data, and previously published data at $E_{\mathrm{p}}=135\mathrm{} \mathrm{and} 178$ MeV, are analyzed in the context of the distorted wave impulse approximation. The transition densities obtained from the proton scattering analysis are compared with those we obtain from fitting the corresponding electron scattering form factors in an attempt to evaluate the validity of the distorted wave impulse approximation at high momentum transfer over the range $E_{\mathrm{p}}=135-800\mathrm{}$ MeV. The proton and electron values of theoretical normalization factors are in reasonable agreement with each other for the unnatural parity states but are in agreement only at the highest proton energies for the natural parity states.

Differential cross sections for inelastic scattering of ${\pi }^{+}$ and ${\pi }^{-}$ from a cooled gas target, enriched in ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ (49.9%), were measured at an incident energy $T_{\pi }=164\mathrm{}$ MeV between ${\theta }_{\mathrm{lab}}=18\mathrm{}° \mathrm{and} 74°$. Data were also taken on a natural oxygen and an enriched ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ target (94.9%) to allow a substraction of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ yields from the data taken with the ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ target. A microscopic distorted wave impulse approximation analysis of five collectively enhanced transitions to the lowest $J^{\pi }={\frac{3}{2}}^{-}, {\frac{5}{2}}^{-}, {\frac{7}{2}}^{-}, {\frac{9}{2}}^{-}, \mathrm{and} {\frac{11}{2}}^{-}$ states in ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ was performed using transition densities from three different models. The data were fitted best with transition densities derived from a large-space shell-model calculation; provided that their $\mathrm{}\left[\mathrm{LSJ}\right]=\left[303\right]\mathrm{}$, isoscalar parts were enhanced by a factor ($1+2\delta$). Both the ${\pi }^{+}$ and ${\pi }^{-}$ data for the five transitions in ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ and the transition to the $3^{-}$ state in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ (6.13 MeV) were fitted using a single polarization charge, $\delta$. Evidence was found for $E2\mathrm{}$ strength near 8 MeV and for $M4\mathrm{}$ strength to two states at 15.7 and 17.1 MeV.

Activation measurements of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,n)${}_{}{}^7{}_{}{}^{}\mathrm{Be}$(g.s.+ 0.43 MeV) total reaction cross section have been made at proton energies of 60—480 MeV. The energy dependence of the total reaction cross section, ${\sigma }_T\mathrm{}\left(E\right)\mathrm{}$, is observed to vary inversely with the incident proton energy up to 480 MeV. These results are consistently lower than those reported earlier by Ward et al. in the energy range of 100-200 MeV, the difference being due to the composite nature (${}_{}{}^7{}_{}{}^{}\mathrm{Li}$Cl) of the targets used in the earlier study. The lithium activation, isospin Clebsch-Gordan ratio, and Monte Carlo code methods for determining neutron efficiencies are now in good agreement (±10%) up to 200 MeV.