We study the energy systematics in light mirror nuclei of the unbound states having predominant single-particle character. For many levels in the mass range A=9–17, the observed Thomas-Ehrmann shift is described very well by a simple potential model. We speculate that the missing partner in ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ of the ${\mathrm{}(1/2)\mathrm{}}^{+}$ state in ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ is observable as a broad continuum with a peak at 0.9 MeV.

Photoneutron angular distributions and differential cross sections have been measured for the reaction ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$(γ,${\mathrm{n}}_0$${)}^{16}$O over the excitation energy region from 10 to 24 MeV. The angle-integrated ground state cross section was obtained and compared to the total photoneutron cross section. The comparison indicates that the ground state channel dominates the pygmy resonance region below $E_{\gamma }$=16 MeV but contributes very little (<10%) to the giant resonance region (near 22 MeV). Legendre coefficients extracted from the angular distribution data suggest that electric dipole transitions make up nearly all of the absorption strength in the region studied except in narrow regions near 10.8, 15.1, 17.3, and 22.3 MeV, where small but significantly nonzero values of the $a_1$ coefficient are observed. Values of the $a_2$ coefficient, interpreted in an E1 approximation, suggest a relatively pure single-particle composition of many of the states observed in the pygmy resonance region from 10 to 16 MeV.

Accurate absolute cross sections for the photodisintegration of deuterium were experimentally determined, using an absorption method, at the following photon energies: 5.97, 7.25, 7.60, 7.64, 8.80, 9.00, and 11.39 MeV with uncertainties generally less than 3%. The photon beams were produced by thermal neutron capture, and the absorption through 2 m absorbers of ${\mathrm{H}}_2$O and ${\mathrm{D}}_2$O was measured. The results are in excellent agreement with theoretical predictions with a preference for calculations using soft core potentials and including explicitly the effects of meson-exchange currents.

The reaction ${}_{}{}^2{}_{}{}^{}(\gamma$,p)n has been studied using a monochromatic and polarized gamma ray beam at energies $E_{\gamma }$=19.8, 29.0, 38.6, and 60.8 MeV. The beam of an intensity ∼4×${10}^5$ γ/sec was obtained by Compton back scattering of mode-locked laser light off electron bunches in the Adone storage ring. Photoneutron yields were measured at nine neutron angles ${\mathrm{theta}}_{\mathrm{n}\mathrm{\simeq }}$15, 30, 45, 60, 90, 120, 135, 150, and 165 deg in the center of mass (c.m.) for $E_{\gamma }$=19.8, 29.0, and 38.6 MeV, and at ${\mathrm{theta}}_{\mathrm{n}\mathrm{\simeq }}$30, 60, 90, 120, and 150 deg c.m. for $E_{\gamma }$=60.8 MeV. The polarization independent component $I_0$(theta) of the differential cross section and the polarization dependent component ${\mathrm{PI}}_1$(theta) were deduced and the angular distribution of the azimuthal asymmetry factor Σ(theta)=$I_1$(theta)/$I_0$(theta) was obtained. An extensive comparison with theory has been carried out and the inclusion of corrections due to meson exchange currents and to Δ-isobar configurations have been shown to be mandatory at energies $E_{\gamma }$≳40 MeV. Theoretical and experimental implications of intermediate energy deuteron photo- disintegration studies are discussed in some detail.

Angular distribution, asymmetry function, and polarization of the outgoing nucleons in deuteron photodisintegration are investigated employing the relativistic one-body charge density and two-body charge and current density effects with local and nonlocal contributions in pseudoscalar and pseudovector pion-nucleon couplings, and comparison is made with available experimental data. The angular distribution and polarization coefficients are reported for the super-soft core, Paris, Yale, and Hamada-Johnston potentials. The relativistic one-body and two-body corrections to the charge density increase the isotropic component of the angular distribution at lower energies but decrease it at higher energies. The changes in the polarization parameters are nearly the same for all the potentials, and all the potentials are found to reproduce the angular distribution, asymmetry function, and polarization of outgoing nucleons quite well at low and medium gamma ray energies.

The level structure of the N=80 nucleus ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pm}$ has been studied in-beam by the ${}_{}{}^{142}{}_{}{}^{}\mathrm{Nd}$(p,2nγ${)}^{141}$Pm reaction using a 25-MeV p beam and by the ${}_{}{}^{141}{}_{}{}^{}(\mathit{\alpha }$,4nγ${)}^{141}$Pm reaction using a 47-MeV α beam. γ-ray singles, γ-γ coincidence (both prompt and delayed), and angular distribution experiments were performed. We found 42 γ rays deexciting 28 states in ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pm}$ from the (p,2nγ) reaction and 34 γ rays deexciting 22 (generally higher-spin) states from the (α,4nγ) reaction, for a total of 35 known states in ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pm}$. These in-beam experiments, taken together with the results from ${}_{}{}^{141}{}_{}{}^{}\mathrm{Sm}_{}^{\mathrm{m}+\mathrm{g}}{}_{}{}^{}$ decay, yield $J^{\pi }$ assignments for most of the states and have allowed us to deduce the configurations for many of the states. The structures are discussed in terms of single-quasiparticle shell-model and triaxial weak-coupled collective states and are compared with systematics for this nuclear region.

Analysis of the ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}$(p,α) reaction with the triton pickup and α knockout models fails to give the magnitude of the measured cross section. We show that a calculation based on a collective form factor successfully gives both the angular distribution and the absolute magnitude of the cross section. Some insight into the collective process is provided by the recent extension of the interacting boson model to alpha clustering in deformed nuclei.

Gamma-ray production cross sections have been measured for the gamma-ray lines most strongly excited in the alpha-particle bombardments of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ for alpha-particle energies from threshold to 27 MeV. Tabulations of cross sections averaged over alpha-particle energy bins of 1 MeV are provided for calculations relevant to gamma-ray line astronomy. Relevance to analysis of spectra acquired with gamma-ray spectrometers in space is discussed.

Twelve known low-lying positive parity levels in ${}_{}{}^{105}{}_{}{}^{}\mathrm{Pd}$ up to 962 keV excitation energy were investigated by measuring, in singles mode, with a high resolution 57 ${\mathrm{cm}}^3$Ge(Li) detector, the yields and angular anisotropies of the deexcitation γ rays following Coulomb excitation with 2 to 4 MeV protons. Out of the seven of these levels which have been populated for the first time through Coulomb excitation with protons, the 696.2 keV level is proposed to be Coulomb excited for the first time. Level energies, the branching ratios, the multipole mixing ratios, B(E2) and B(M1) transition probabilities, and half-lives were deduced. The angular distributions support ${\mathrm{}(5/2)\mathrm{}}^{+}$, ${\mathrm{}(3/2)\mathrm{}}^{+}$, ${\mathrm{}(7/2)\mathrm{}}^{+}$, ${\mathrm{}(5/2)\mathrm{}}^{+}$, and ${\mathrm{}(3/2)\mathrm{}}^{+}$ spin-parity assignments, for the 560.6, 673.2, 696.2, 781.8, and 961.9 keV levels, respectively. The present results have been discussed in view of the existing experimental data, as well as in terms of various core-particle coupling models.

A level scheme for ${}_{}{}^{220}{}_{}{}^{}\mathrm{Ra}$ is presented, established using the ${}_{}{}^{208}{}_{}{}^{}\mathrm{C}$,2n) reaction studied near the Coulomb barrier (60≤E≤68 MeV). Measurements included γ-ray excitation functions, γ-γ coincidences, and γ-ray angular distributions. The dominant features in the spectrum are states of alternating parity connected by fast E1 transitions. Values of B(E1)/B(E2) are obtained for states with J=6–17 ħ. Examination of the systematic behavior of even-even Ra isotopes reveals a sharp change in structure as one proceeds from ${}_{}{}^{214}{}_{}{}^{}\mathrm{Ra}$ to ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$. Results are discussed in terms of alpha-particle clustering (in particular as described by the vibron model) and of a stable octupole deformation; calculations of the energy spectrum based on the vibron model are presented.

The reaction ${}_{}{}^{70}{}_{}{}^{}\mathrm{O}$,2p2n${)}^{82}$Sr with E${(}^{16}$O)=80 MeV was used to study the nucleus ${}_{}{}^{82}{}_{}{}^{}\mathrm{Sr}$. Measurements were made of the excitation functions, angular distributions, and γ-γ-t coincidences. From these measurements six new levels were placed in the level scheme of ${}_{}{}^{82}{}_{}{}^{}\mathrm{Sr}$ at 2683.7, 3609.2, 4367.1, 5308.4, 6364.4, and 7827.8 keV. A gamma ray with a very high anisotropy [$A_2$=-1.05(7), $A_4$=0.12(6)] feeds the ${(11\mathrm{}}^{\mathrm{-}}$) level at 5914.5 keV. A new band based on the level at 3525.7 keV was identified. The sequence of transitions decaying down the negative parity band was reordered to 522-1005-876-694 keV.

Small angle cross sections for the reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{20}$Ne,α${)}^{28}$Si and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{20}$Ne${,}^8$Be${)}^{24}$ Mg leading to ground states and first excited states are reported for $E_{\mathrm{c}.\mathrm{m}.\mathrm{}\mathrm{\sim }12}$ to 15 MeV and angular distributions are measured at 11 selected energies. A few resonant-like features are found with dominant single l values determined as l=8, 9, 10, and 11. Although individually these features satisfy previously accepted resonance criteria, the energies and l values are not sufficiently consistent with those of other heavy-ion resonance investigations of ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ to interpret them as resonances of common origin.

The time-dependent cluster model is applied to the description of light-ion reactions of various types. Special emphasis is placed on the quantitative description of the fusion excitation function in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{-}_{}^{12}{}_{}{}^{}$C system and the qualitative discussion of l matching for different binary reactions in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{-}_{}^{16}{}_{}{}^{}$O system. The Euler-Lagrange equations of the time-dependent cluster model are generalized to the multideterminantal case, and in this form they are applied to describe the evolution of parity-projected wave functions in the α${\mathrm{-}}^{12}$C reaction. For this reaction, the results for various assumptions about the trial wave function and the initial geometry of the reaction are qualitatively discussed.

Targets of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ have been bombarded by 35 MeV/nucleon ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ ions. Inside a cone of ±10° around the beam axis, outgoing protons and α particles were detected by an arrangement of 18 scintillators in coincidence with particles of charge Z=5–11 emerging at 2°. At this energy the identified reaction mechanisms differ significantly from the ones observed in the 10–15 MeV/nucleon region. Important energy transfer of around 50 MeV to the target-like residues is observed. For the coincident oxygen-α events, in addition to the well-known sequential decay mechanism of the projectile, about 40% of the events are attributed to another mechanism producing oxygen ions narrowly peaked near the beam velocity. Among the other reaction channels, cases are present which can be interpreted in terms of sequential decay alone, as well as others where admixtures of different processes play a role.

We calculate the imaginary part of the heavy ion optical potential at the strong absorption radius assuming that the absorption is essentially given by the depopulation of the entrance channel due to nucleon transfer. The transfer probabilities of individual nucleons between specific quantum states are calculated with a simple formula. The method is applied to several pairs of nuclei and the results are compared to the experiment and other previous calculations.

Fission yields from the photofission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ with neutron capture γ rays were measured at an effective excitation energy $E_x$=7.8 MeV. The mass distribution of the fission fragments was deduced by measuring yields of 19 mass chains with respect to ${}_{}{}^{135}{}_{}{}^{}\mathrm{Xe}$, whose cumulative yield was measured directly. The results are in general agreement with those obtained by Jacobs et al. using bremsstrahlung at higher energies. However, a systematic decrease of the yields of a few mass chains was observed. This decrease can be attributed to a change in the shape of the light and heavy mass distributions, as a function of energy. The ratio ${\Gamma }_{\mathrm{n}/{\Gamma }_f}$ was measured at two energies and its values confirm recent theories on the shape and height of the second fission barrier in ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. The most probable charge $Z_p$ was obtained for the mass chains 92, 134, and 135 at three energies.

Differential cross sections have been measured for p+d→γ${+}^3$He at $T_{\mathrm{p}}$(lab)=300, 350, 400, 425, 450, 470, and 500 MeV for ${\mathrm{theta}}_{\gamma }$(c.m.) near 60° and 90°. Measurements were also made for d+p→γ${+}^3$He at $T_{\mathrm{d}}$=376 MeV for ${\mathrm{theta}}_{\gamma }$(c.m.)=84°, 98°, and 113°, and at $T_{\mathrm{d}}$=600 MeV for ${\mathrm{theta}}_{\gamma }$=96° and 105°. Our results are in agreement with those of the inverse reaction, γ${+}^3$He→p+d of Sober et al., as is expected from time-reversal invariance. Our data agree with the latest results of Cameron et al. The older radiative capture measurements of Heusch et al. and the photodisintegration measurements made at other laboratories differ significantly from our results. Our data are compared with three theoretical models; the one proposed by Maximon and Prats comes closest to describing the data.

Delta excitations in heavy nuclei, induced by charge exchange reactions, are studied using the surface response model. The residual pion-exchange interaction and the self-energy of the delta in a nuclear medium is included in the random-phase-approximation response. The peak position observed in ${(}^3$He,t) reactions can be explained by the self-energy of the delta extracted from pion-nucleus scattering, and the magnitude of the cross section is consistent with Glauber theory. The comparison to (p,n) data is reasonable; contributions from neutron decay of the delta, which are left out in the calculations, constitute a substantial experimental background.

Single arm spectrometer measurements of the differential cross sections and analyzing powers of the pp→pn${\pi }^{+}$ reaction have been performed at 400 and 450 MeV incident proton energy. The measurements covering an angular range from 46° to 90° (lab) spanned pion energies corresponding to production of the np system with relative energies between 0 and 30 MeV, a region where the influence of the np final state interaction is particularly important. The trend of the measured analyzing power is very similar to that of the pp→d${\pi }^{+}$ reaction, and is well explained by calculations that use this latter data as input. Dominance of the triplet pn final state is implied by these results.

Energy spectra of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ emitted in the reactions of 70- and 160-MeV ${\pi }^{\pm }$ mesons with Ag were measured at seven angles with respect to the beam, from 30° to 160°. The spectra are similar in both shape and magnitude to the corresponding spectra observed at an angle of 90° in the reactions of 300–480 MeV protons with the same target. The spectra from ${\pi }^{\pm }$ reactions are nearly independent of angle, in contrast to the strong angular dependence of the high-energy particles observed in reactions of protons and other projectiles. These observations, as well as the ${\pi }^{+}$/${\pi }^{\mathrm{-}}$ ratios for the yields of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, are interpreted in terms of pion absorption and subsequent interactions of the resulting fast nucleons leading to fragment emission.