The prediction of transverse energy distributions, dσ/${\mathit{dE}}_{\mathit{t}}$, in heavy ion collisions is examined and extended and the evidence for the effect of anomalous cross section fluctuations on the cross section at high transverse energy is critically examined. We calculate the contribution to the transverse energy of rescattering of target nucleons on their unstruck neighbors.

The proton Compton effect has been studied in the region between the threshold for pion photoproduction and the Δ(1232). The measurements were performed using bremmstrahlung from the high duty-factor electron beam available at the Saskatchewan Accelerator Laboratory. Elastically scattered photons were detected with an energy resolution of approximately 1.5% using a large NaI total absorption scintillation detector. Differential cross sections were measured for photon energies in the range 136 MeV≤${\mathit{E}}_{\gamma }$≤289 MeV and for angles in the range 25°<${\mathrm{\theta }}_{\mathrm{lab}}$<135°. The angular distributions and the excitation functions derived from these data are in agreement with recent theoretical analyses. The results were interpreted within a formalism based in part on dispersion relations to obtain model-dependent estimates of the electric and magnetic polarizabilities, α¯ and β¯. We find, subject to the dispersion sum rule constraint α¯+β¯=(14.2±0.5)×${10}^{\mathrm{-}4}$ ${\mathrm{fm}}^3$, that α¯=(9.8±0.4±1.1)×${10}^{\mathrm{-}4}$ ${\mathrm{fm}}^3$ and β¯=(4.4∓0.4∓1.1)×${10}^{\mathrm{-}4}$ ${\mathrm{fm}}^3$, which are consistent with the best previous measurements.

Recent proton Compton scattering data from Saskatoon spanning the pion threshold region are shown to reflect the presence of a unitarity cusp (Wigner cusp), long predicted but never before observed. The analysis is based on a formulation of the Compton cross section employing convenient semiphenomenological expressions for the four dominant multipole amplitudes, designed to respect the low energy theorem and other constraints. Unitarity anomalies have now been detected in both the elastic (Compton) and inelastic (${\mathrm{\pi }}^0$p) channels of the γ+p reaction.

We present in detail a formulation of the shell model as a path integral and Monte Carlo techniques for its evaluation. The formulation, which linearizes the two-body interaction by an auxiliary field, is quite general, both in the form of the effective ‘‘one-body’’ Hamiltonian and in the choice of ensemble. In particular, we derive formulas for the use of general (beyond monopole) pairing operators, as well as a novel extraction of the canonical (fixed-particle-number) ensemble via an activity expansion. We discuss the advantages and disadvantages of the various formulations and ensembles and give several illustrative examples. We also discuss and illustrate calculation of the imaginary-time response function and the extraction, by maximum entropy methods, of the corresponding strength function. Finally, we discuss the ‘‘sign problem’’ generic to fermion Monte Carlo calculations, and prove that a wide class of interactions are free of this limitation.

We investigate the behavior of the operator responsible for sequential pion double charge exchange in nuclei in the plane wave limit with a view to studying its extension in space, especially the short-range part.

We extend a recent calculation of the momentum dependence of the ρ-ω mixing amplitude to the pseudoscalar sector. The π-η mixing amplitude is calculated in a hadronic model where the mixing is driven by the neutron-proton mass difference. Closed-form analytic expressions are presented in terms of a few nucleon-meson parameters. The observed momentum dependence of the mixing amplitude is strong enough as to question earlier calculations of charge-symmetry-breaking observables based on the on-shell assumption. The momentum dependence of the π-η amplitude is, however, practically identical to the one recently predicted for ρ-ω mixing. Hence, in this model, the ratio of pseudoscalar-to-vector mixing amplitudes is, to a good approximation, a constant solely determined from nucleon-meson coupling constants. Furthermore, by selecting these parameters in accordance with charge-symmetry-conserving (CSC) data and SU(3)-flavor symmetry, we reproduce the momentum dependence of the π-η mixing amplitude predicted from chiral perturbation theory. Alternatively, one can use chiral-perturbation-theory results to set stringent limits on the value of the NNη coupling constant.

In order to develop a procedure for calculation of pion absorption on ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, we perform the decomposition of the absorption amplitude in three-nucleon partial waves, with full inclusion of antisymmetrization effects among the nucleons. Within this formalism, the matrix elements of the Δ-rescattering term, believed to be the dominant elementary absorption mechanism, are evaluated and embedded in the full (Faddeev-based) nuclear dynamics. This implies the treatment of the 3←3 and 2←3 processes in the final state. Since no attempt is made to include distortions due to the four-body (πNNN) dynamics, the trinucleon bound-state wave function is the only requirement in the initial state.

The magnetic moment and lifetime of the 19/$2^{\mathrm{-}}$, 4.367 MeV state in ${}_{}{}^{49}{}_{}{}^{}\mathrm{Cr}$ have been measured in a transient magnetic field experiment. The nuclei were excited in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{40}$Ca,2pn${)}^{49}$Cr reaction and recoiled in a thick polarized gadolinium foil. The field strength was calibrated by a simultaneous g-factor measurement of excited states in ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}$ and ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ti}$. The mean lieftime, found from Doppler-shifted line-shape analysis, is τ(19/$2^{\mathrm{-}}$)=2.7(2) ps and the g factor is g=+0.78(12). The g value implies a substantial ${\mathit{f}}_{7/2}$ proton contribution to the total spin of this state and the result is discussed in terms of both the shell model and the cranked shell model.

The structure of ${}_{}{}^{147}{}_{}{}^{}\mathrm{Pr}$ has been investigated by performing measurements of γ-ray and conversion-electron singles and γγ coincidence spectra of mass separated sources of 56-s ${}_{}{}^{147}{}_{}{}^{}\mathrm{Ce}$. The proposed level scheme extends the known structure of ${}_{}{}^{147}{}_{}{}^{}\mathrm{Pr}$ to an energy of 2.2 MeV and includes several levels below 1.2 MeV that have not been identified in previous decay studies of ${}_{}{}^{147}{}_{}{}^{}\mathrm{Ce}$. Measurement of the conversion coefficients for several transitions has led to the assignment of negative parity to the levels at 362, 452, 467, and 608 keV in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Pr}$, which show properties similar to low-energy negative-parity states identified in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Pr}_{86}^{}{}_{}{}^{}$, ${}_{}{}^{145}{}_{}{}^{}\mathrm{La}_{88}^{}{}_{}{}^{}$, and ${}_{}{}^{149}{}_{}{}^{}\mathrm{Pm}_{88}^{}{}_{}{}^{}$. The presence of low-energy negative-parity states suggests that configurations having significantly different deformation, related to the highly deformed region above N=90 and/or to the reflection asymmetric region identified around ${}_{}{}^{145}{}_{}{}^{}\mathrm{Ba}$, may manifest themselves at low energy in these nuclides.

The absolute electrofission cross sections of Au and Ta were measured in the range 25–180 MeV. The deduced photofission cross section shows, for both Au and Ta, a pronounced dip around the photopion threshold (∼140 MeV). This (γ,f) dip is interpreted as a consequence of a probable photopion absorption in a ‘‘stopped pion regime.’’

The neutron total cross section for natural indium was measured for ${\mathit{E}}_{\mathit{n}}$=25–500 eV with the time-of-flight method at the Los Alamos Neutron Scattering Center. The neutron capture reaction was studied on a highly enriched sample (99.99%) of ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$. A total of 47 previously unreported resonances were observed. The combination of the two measurements allowed assignment of the new resonances to ${}_{}{}^{113}{}_{}{}^{}\mathrm{In}$ or ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$. Resonance parameters were extracted for all of the neutron resonances observed.

In beam γ-ray spectroscopic studies of ${}_{}{}^{91}{}_{}{}^{}\mathrm{Mo}$ (up to 33/2ħ, 6 MeV) and ${}_{}{}^{89}{}_{}{}^{}\mathrm{Nb}$ (up to 29/2ħ, 6.5 MeV) are reported using fusion evaporation reactions with ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ beams and enriched target of ${}_{}{}^{66}{}_{}{}^{}\mathrm{Zn}$. The level schemes are well described by spherical shell-model calculations involving neutrons and protons in 1${\mathit{g}}_{9/2}$ and 2${\mathit{p}}_{1/2}$ orbitals. The experimentally determined transition probabilities are in reasonable agreement with single particle transition probabilities (Weisskopf estimates).

Yrast and yrare states in the nucleus ${}_{}{}^{89}{}_{}{}^{}\mathrm{Nb}$ have been studied in the reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{36}$Ar,5p) by measuring γγ coincidences and directional correlation orientation with the OSIRIS array. In addition, γ-ray singles angular distributions have been taken with the reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{35}$Cl,4p). Up to the highest spins observed (37/$2^{+}$,33/$2^{\mathrm{-}}$), the states identified line up with the ones predicted by the spherical shell model, taking into account three proton particles and two neutron holes in the ${\mathit{g}}_{9/2}$ and ${\mathit{p}}_{1/2}$ single-particle orbits. The shell model also reproduces most of the measured branching and E2/M1 mixing ratios. The mean lifetime of the 2152 keV 17/$2^{\mathrm{-}}$ yrast state was determined as 0.74(7) ns.

The level structure of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Mo}$ has been studied with the ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$${(}^{32}$S,2pn) reaction at 110 MeV beam energy. Mainly two bands of γ rays depopulating states of probable spin-parity values ranging up to (27/2${)}^{+}$ were determined from the excitation function, neutron and γ-γ coincidences, and γ-ray angular distributions. The high-spin states of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Mo}$ show a scheme very similar to that of the ${}_{}{}^{87}{}_{}{}^{}\mathrm{Zr}$ isotone. The interpretation of these states in terms of the three neutron-hole configuration (ν${\mathit{g}}_{9/2}$${)}^{\mathrm{-}3}$ and core-excited states is discussed.

Inelastic ${\mathrm{\pi }}^{\pm }$ cross-section measurements at a pion incident energy of 162 MeV were made for 12 previously known $6^{\mathrm{-}}$ states in ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$. The peak resolution was significantly improved over a previous ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$(π,π’) report describing only two $6^{\mathrm{-}}$ states. Using both harmonic oscillator and Woods-Saxon wave functions (unbound as necessary), the pion scattering data were combined with electron scattering data to determine the isoscalar magnetic structure coefficients for each state. Although more streched transitions have been located by pion scattering on ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ than in any other nucleus, the total isoscalar strength was only 12% of the extreme single particle sum rule, and only about 1/4 of that predicted by more complete calculations. Discrepancies between the isoscalar strengths for several of these states and those found from a combined electron-proton scattering analysis are pointed out.

The interaction between the yrast and yrare bands is discussed in the case of five particles in the single-j shell model space with j=13/2. Comparison between the case of four and five particles in the same model space is made and it is shown that the interaction between the yrast and yrare bands in the five-particle system is stronger than that in the four-particle system. The results of the Hartree-Fock-Bogoliubov cranking (HFBC) method are compared with those obtained from the diagonalization of the cranking model Hamiltonian and it is shown that the HFBC method is insufficient for describing the band crossing in the five-particle system.

The neutron skin is studied in terms of the Hartree-Fock calculation, and its new definition is presented and discussed. It turns out that the neutron skin is closely related to how far the nucleus is away from the β stability line, but not directly to the number of excess neutrons. Related properties of Hartree-Fock calculations for unstable nuclei are discussed. Novel features associated with the neutron skin are suggested, for instance, neutron avalanche in reactions involving a nucleus with the neutron skin. The formation of the proton skin is shown to be rather difficult.

The microscopic corrections to the liquid drop energy are determined by a method that takes simultaneously into account shell and pairing effects. For this purpose, a level density with explicit dependence on pairing correlations is defined from the particle number conservation condition in the BCS theory. This density is expressed in terms of the Dirac δ-generalized function and its derivatives. This enables one to deduce the expansion of this density as a series of Hermite polynomials. The microscopic corrections are then determined by a procedure which is analogous to that of Strutinsky. The method permits also to define an average pairing gap which depends both on the nucleon type (neutron or proton) and on the nuclear shape. When applied to the ground state energy calculations for the even-even actinide nuclei, with a deformed Woods-Saxon mean field, this method leads to a very good agreement between the calculated and the experimental values.

The excitation functions and the mass yield curves for proton-induced fissions of ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$, and ${}_{}{}^{243}{}_{}{}^{}\mathrm{Am}$ targets were studied. The excitation functions for near-symmetrically divided fragments were found quite different in shapes and threshold energies from those of asymmetrically divided ones in all the fissioning systems studied. In order to obtain the fission barrier heights for symmetric and asymmetric mass division, the conventional Bohr-Wheeler type calculations for the competition between fission and neutron emission were performed. In the calculation, two independent fission channels, symmetric and asymmetric, were assumed, and fission barrier heights and level density parameters that could best reproduce the shapes of the excitation functions (incident energy dependence) of typical symmetric and asymmetric products were deduced. Barrier heights for symmetric and asymmetric mass divisions both decrease as the mass of fissioning nuclide ${\mathit{A}}_{\mathit{f}}$ increases, and they also exhibit slight dependence on the atomic number. Difference between the two barrier heights is 2.0–2.5 MeV in the region of ${\mathit{A}}_{\mathit{f}}$=236–245. From similar analysis of excitation function data reported in literature, it is found that the difference changes from a large positive value for N∼150, neutron number of the fissioning nuclide, to a large negative value for N∼126, and the two barrier heights become comparable at N=135–138.

The Gamow-Teller (GT) strength functions of ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ measured by recent charge-exchange experiments have been studied using shell-model calculations employing two model spaces. The shell model is fairly successful at reproducing GT strength in the (p,n) direction, but the agreement is not as good in the (n,p) direction. It is found that both directions can be fit consistently by shifting single particle energies in a systematic manner. It is found that roughly 75% of the sum-rule strength can be seen in the experiments for both ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$. It is also found that roughly 35% of the GT strength predicted by the shell model is seen in the (n,p) direction for all three nuclei, but that the quenching in the (p,n) direction varies with nucleus. The consequences of these findings for improving the calculation of weak interaction rates are discussed.