The process of nuclear fission induced by electrons or other charged leptons is analyzed using distorted electron wave functions and interpreted in terms of virtual photon exchange, thus relating electrofission to photofission. Comparison of cross sections and fission fragment angular distributions for photofission, electrofission, and positrofission is shown to lead to reasonable conclusions in terms of the contributions of different multipoles and intermediate states. The effects of electron distortion are found to be considerable. As a method of analysis of fission, especially near threshold, inclusive and exclusive electrofission experiments and also the ratio of electron to positron cross sections promise good results.

The (nonperturbative) coupled cluster method is applied to the pion-nucleon system. After solving the vacuum and one-nucleon problem, a reasonable description of the deuteron is obtained.

A formalism for investigating the positron-capture reaction ${\mathrm{e}}^{+}$+d→ν${¯}_{\mathrm{e}+\mathrm{p}+\mathrm{p}}$ at medium positron energy (i.e., 0.5–2.0 GeV) and small p-p excitation energies (i.e., $E_{\mathrm{rel}\mathrm{\le }10}$ MeV) is described. In view of the small p-p excitation energy $E_{\mathrm{rel}}$ being considered, we take into account only the ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{P}_{\mathrm{J}}^{}{}_{}{}^{}$ p-p final states (J=0, 1, 2). For the polar vector current, an impulse approximation, modified to incorporate current conservation, is employed and additional meson-exchange currents are included in the dominant channel. For the axial vector current, the nucleon-only impulse approximation is used. Numerical results are presented to highlight the prospect of measuring the $q^2$ dependence of the nucleon axial form factor $f_A$($q^2$). The proposed precision measurement of the nucleon axial form factor may be feasible at the upcoming Continuous Electron Beam Accelerator Facility if the proposed positron ring can actually be constructed.

Making use of a formalism previously developed by Hwang, Henley, and Miller, we obtain numerical predictions for the electron scattering double differential cross section and the parity-violating asymmetry (caused by Z-boson exchange), both defined in the laboratory frame, for the kinematics suitable for the upcoming Continuous Electron Beam Accelerator Facility. For the kinematic regime characterized by $q^2$≤15 ${\mathrm{fm}}^{\mathrm{-}2}$ and $E_{\mathrm{rel}\mathrm{\le }10}$ MeV with $q^2$ and $E_{\mathrm{rel}}$, respectively, the four-momentum transfer squared and the n-p excitation energy, the asymmetry is of order ${10}^{\mathrm{-}5}$–${10}^{\mathrm{-}4}$ while the cross section remains large, so that a precision test of the standard Glashow-Weinberg-Salam electroweak theory may be attempted. For the kinematic regime characterized by $q^2$≥30 ${\mathrm{fm}}^{\mathrm{-}2}$ and $E_{\mathrm{rel}\mathrm{\le }10}$ MeV, the asymmetry may be of order ${10}^{\mathrm{-}3}$ so that one may attempt an experiment at backward scattering angles to extract interesting information regarding the large $q^2$ behavior of the nucleon electromagnetic and weak form factors.

Angular distributions of the differential cross sections and analyzing powers of the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$(p,${\pi }^{\mathrm{-}}$) and ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$(p,${\pi }^{\mathrm{-}}$) reactions leading to both discrete final states and the continuum have been measured at $T_{\mathrm{p}=201\mathrm{}}$ MeV. The two reactions exhibit quite similar selectivities and angular distributions. For the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$(p,${\pi }^{\mathrm{-}}$${)}^{19}$Ne reaction, the strongest transitions are to known high spin states, which are favored by the high momentum transfer of the reaction. These states are presumed to have predominantly two-particle–one-hole configurations with respect to the target nucleus because of the two-nucleon nature of the reaction mechanism. It is conjectured that the states most strongly populated in the ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$(p,${\pi }^{\mathrm{-}}$${)}^{27}$Si reaction have a similar structure.

We investigate the effect of the Pauli principle in π-nucleus scattering. Descriptions are made in terms of the optical potential based on the multiple scattering formalism and a prescription is given for incorporating the Pauli effect. Detailed examinations are performed for π-d, ${\mathrm{-}}^3$He, and ${\mathrm{-}}^4$He scattering in the energy range $T_{\pi }$=50–300 MeV. The Pauli effect is found to cause an important medium correction in both low and intermediate energy regions, and this aspect is emphasized for the more strongly correlated nucleus. Attention is paid to the πN partial wave mixing. It is seen that the mixing between the $P_{33}$ and the other partial waves gives a non-negligible contribution throughout the energy range considered.

An analysis of low energy pion-nucleon charge exchange and elastic scattering data is presented. A system of coupled channels with nonlocal potentials is used to include the effects of the Coulomb interaction, pion and nucleon mass differences, and the photoabsorption channel. By using recent accurate charge exchange data, redundancies exist, allowing cross checks between data sets. The cross section for ${\pi }^{+}$n→${\pi }^0$p is deduced and a value of $a_1$-$a_3$=0.290±0.008 ${\mu }^{\mathrm{-}1}$ is extracted.

The production of neutral pions has been studied in reactions of 35 MeV/nucleon ${}_{}{}^{14}{}_{}{}^{}$N${+\mathrm{}}^{27}$Al,Ni,W and 25 MeV/nucleon ${}_{}{}^{16}{}_{}{}^{}$O${+\mathrm{}}^{27}$Al,Ni. Inclusive pion differential distributions dσ/${\mathrm{dT}}_{\pi }$, dσ/dΩ, dσ/dy, dσ/${\mathrm{dp}}_{\perp }$, and $d^2$σ/dy ${\mathrm{dp}}_{\perp }$ have been measured by detecting the two pion-decay γ rays in a setup of 20 lead glass Čerenkov detector telescopes. Special care was taken to understand and suppress background events. Effects of pion reabsorption are discussed and it is found that the cross sections presented here are substantially affected by such final state interactions. The comparatively large experimental cross sections and the shape of the spectral distributions cannot be accounted for in single nucleon-nucleon collision or statistical models; they rather call for a coherent pion production mechanism.

The (${\pi }^{+}$,pd) reactions on ${}_{}{}^6{}_{}{}^{}$Li and ${}_{}{}^7{}_{}{}^{}$Li have been studied at $T_{\pi }$=59.4 MeV. Triple- and single-differential cross sections for these reactions are presented. The data are fitted to a T matrix and compared to the ${}_{}{}^3{}_{}{}^{}$H(${\pi }^{+}$,p${)}^2$H reaction. A model in which the pion interacts and is absorbed on a ‘‘quasi-triton’’ cluster describes the main features of the data very well. An extrapolation of our data into unmeasured regions of phase space suggests that about 8% of the pion absorption cross section on ${}_{}{}^6{}_{}{}^{}$Li at 59.4 MeV goes into the (${\pi }^{+}$,pd) channel. The ${}_{}{}^7{}_{}{}^{}$Li(${\pi }^{+}$,${\mathrm{p}\mathrm{d})}^4$He(2 ${}_{}{}^{\mathrm{-}}{}_{}{}^{}$) transition at 22.1 MeV excitation appears to be strongly populated. This is a surprise because it is not seen in the ${}_{}{}^7{}_{}{}^{}$Li(p,α${)}^4$He reaction.

In pion-nucleus scattering near 50 MeV, the Coulomb and nuclear amplitudes are comparable for a fairly wide range of angles. The interference of these amplitudes makes small nuclear structure effects observable in elastic scattering. As a result, energy dependent optical model analyses of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ do not reproduce the observed 50 MeV cross sections. Including the ground and first excited state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ in a coupled-channel calculation provides a consistent interpretation of both the elastic and inelastic data between 20 and 100 MeV.

The constraint of a sharp bag boundary in the bag model is relaxed in the present work. This has been achieved by replacing the square-well potential of the bag model by a smooth scalar potential and introducing a term similar to the bag pressure term. The constraint of the conservation of the energy-momentum tensor is used to obtain an expression for the added bag pressure term. The model is then used to determine the static properties of the nucleon. The calculation shows that the rms charge radius and the nucleon magnetic moment are larger than the corresponding bag model values. Also, the axial vector coupling constant and the πNN coupling constant are in better agreement with the experimental values.

Differential cross sections for ${\pi }^{\pm }$ elastic scattering on ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ at a pion kinetic energy of 164 MeV were measured over the angular range 20°–91°. A contaminant analysis was performed for the target sample based on the kinematic separation of the elastic scattering peaks and the use of previously measured or calculated elastic cross sections. The data are compared to a newly developed, momentum-space, optical-potential calculation which shows clearly the importance of including Pauli suppression and three-body kinematics in the microscopic scattering description.

The ratios of g factors of the first excited states of the ${}_{}{}^{107}{}_{}{}^{}$,109Ag isotopes, g((3/2))/g((5/2))=1.5(3) and 2.3(5), respectively, have been measured by the perturbed angular correlation transient field technique. The absolute magnitudes of the g factors have been obtained through a calibration procedure that makes use of the magnetic dipole moments of the first $2^{+}$ states of ${}_{}{}^{106}{}_{}{}^{}\mathrm{Pd}$ and ${}_{}{}^{110}{}_{}{}^{}\mathrm{Cd}$ and are ${}_{}{}^{107}{}_{}{}^{}\mathrm{Ag}$: g${\mathrm{}\left(\right(3/2\mathrm{})\mathrm{}}_1^{\mathrm{-}}$)=0.61(12), g${\mathrm{}\left(\right(5/2\mathrm{})\mathrm{}}_1^{\mathrm{-}}$)=0.41(7) and ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}$: g${\mathrm{}\left(\right(3/2\mathrm{})\mathrm{}}_1^{\mathrm{-}}$)=0.66(10), g${\mathrm{}\left(\right(5/2\mathrm{})\mathrm{}}_1^{\mathrm{-}}$)=0.29(6). These results are compared with weak coupling calculations as well as with Nilsson models with symmetric or triaxial cores. The latter reveal a sensitive dependence of the g factors on the deformation parameter γ. .AE

The two odd-odd nuclei dynamical symmetries proposed by Balantekin and Paar and by Van Isacker et al. are examined in detail. In particular, the question of the general applicability of the concept of hole-hole and hole-particle representations are compared in detail for both dynamical symmetries, the latter being related to neutron subshell closure. It is found that while the hole-hole and hole-particle representations are vastly different in the Balantekin and Paar dynamical symmetry, the neutron subshell closure has little, if any, effect on the dynamical symmetry of Van Isacker et al. Implications of this finding are discussed.

A study of Pauli exchange effects for the odd particle in the interacting boson-fermion model is made by a comparison with a core-quasiparticle coupling model based on dynamical field theory and the BCS method. Spectra for a partly filled j shell coupled to interacting boson model cores are calculated in both models. Values of the interacting boson-fermion model exchange parameter ${\Lambda }_0$ are found which lead to about the same spectra as in the core-quasiparticle coupling model. Variations of ${\Lambda }_0$ around this value can alter the energy spectra and the Coriolis mixing between bands much more than variations of the corresponding BCS parameter Δ. However, variations of ${\Lambda }_0$ also effectively alter the position of the Fermi level, which should set constraints on phenomenological applications of the interacting boson-fermion model.

We present systematic calculations on nuclei in the region around A=190 within the framework of the proton-neutron interacting boson-fermion model. Energy levels and electromagnetic properties of both positive and negative parity states in odd proton ${(}_{77}$Ir${,}_{79}$Au) and odd neutron ${(}_{78}$Pt) nuclei are compared with experimental data. A general good agreement is obtained with a few adjustable parameters.

The particle-hole interacting boson approximation proposed by Feshbach and Iachello is applied to the low-lying excited states of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Ni}$. Since the particle-hole interaction seems to be dominant in the low-lying excited states in ${}_{}{}^{56}{}_{}{}^{}\mathrm{Ni}$, the particle-hole pairs are taken as the bosons. The rest of the Hamiltonian is considered as the interactions between the bosons. The first excited $2_1^{+}$ and $4_1^{+}$ states as well as the ground state are reasonably described without introducing any artificial treatments into the calculation. The first excited $0_1^{+}$ state is shown to be the two-boson dominant state which is consistent with the experimental prediction. The forbidden components for a fermion system inherent in the boson wave function are investigated. As the result, the wave functions of the $0_g^{+}$, $2_1^{+}$, and $4_1^{+}$ states are shown to be almost free of mixing of the components.

The predictions of the exact SU(3) symmetry limit of the interacting boson model are reviewed for the Dy–Pt region. Evidence of a functional relationship of the coefficient α of the L(L+1) term in the expression for energy in the SU(3) limit with the product $N_{\mathrm{p}{N}_{\mathrm{n}}}$ is presented, with a similar relation for B(E2,$2_1^{+}$-$0_1^{+}$). In contrast, the absence of a simple direct relationship of the coefficient β (=K) of C(λ,μ) or of the SU(3) symmetry breaking term K’’/K with $N_{\mathrm{p}}$,$N_{\mathrm{n}}$ is illustrated. The possible reasons are discussed.

The differential cross section for the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,${\mathrm{p}}_0$${)\mathrm{}}^{39}$K process has been measured in the energy range $E_{\gamma }$=100–300 MeV at laboratory angles of 45°, 90°, and 135°. The cross section for the (γ,p) reaction leaving ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ in its ground state was extracted from the tip region of the proton spectra measured at a series of bremsstrahlung endpoint energies. The data are compared with a distorted-wave impulse-approximation calculation based on a direct, single-particle knockout mechanism.

The mass and charge distributions of heavy residues in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ (15 and 30 MeV/nucleon)- and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ (30 MeV/nucleon)-induced reactions on ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$, ${}_{}{}^{144}{}_{}{}^{}$,150,152,154Sm, and ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$ have been determined from delayed gamma-ray emission. The average produced masses and charges are deduced. A comparison with evaporation calculations following complete and incomplete fusion processes is presented.