At high level density of nuclear states, a separation of diffferent time scales is observed (trapping effect). We calculate the radial profile of partial widths in the framework of the continuum shell model for some $1^{\mathrm{-}}$ resonances with 2p-2h nuclear structure in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ as a function of the coupling strength to the continuum. A correlation between the lifetime of a nuclear state and the radial profile of the corresponding decay process is observed. We conclude from our numerical results that the trapping effect creates structures in space and time characterized by a small radial extension and a short lifetime.

The generalized momentum distribution n(p,Q), related to the half-diagonal two-body density matrix ${\mathrm{\rho }}_{2\mathrm{h}}$(${\mathbf{r}}_1$,${\mathbf{r}}_2$,${\mathbf{r}}_1^{\prime }$) by Fourier transformation in the variables ${\mathbf{r}}_1$-${\mathbf{r}}_1^{\prime }$ and ${\mathbf{r}}_1$-${\mathbf{r}}_2$, plays a key role in the description of final-state interactions in the nuclear medium and other strongly interacting many-body systems. The function n(p,Q) is explored for two Jastrow-correlated models of infinite nuclear matter within a Fermi hypernetted-chain procedure. Significant departures from ideal Fermi gas behavior in certain kinematic domains provide signatures of the strong short-range correlations contained in these models. However, such deviations are less prominent than in earlier calculations based on low-order cluster truncations; correspondingly, violations of the sequential relation are greatly reduced. Simple prescriptions for improved low-cluster-order approximations to n(p,Q) are suggested by analysis of the results of the Fermi hypernetted-chain evaluation. These results are also used to assess the quality of Silver's approximation n(p,Q)≈n(p)[S(Q)-1] for the generalized momentum distribution in terms of the ordinary momentum distribution n(p) and the static structure function S(Q), with findings that have potential implications for the interpretation of data from inclusive electron scattering by nuclei at high momentum transfers.

Alpha-particle widths calculated in a potential model demonstrate that the 7.12-MeV, $4_2^{+}$ state of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ has about the right alpha width for the dominant four-particle–two-hole $4^{+}$ state.

After a brief review of various mappings of fermion pairs to bosons, we rigorously derive a general approach. Following the methods of Marumori and Otsuka, Arima, and Iachello, our approach begins with mapping states and constructs boson representations that preserve fermion matrix elements. In several cases these representations factor into finite, Hermitian boson images times a projection or norm operator that embodies the Pauli principle. We pay particular attention to truncated boson spaces, and describe general methods for constructing Hermitian and approximately finite boson image Hamiltonians. This method is akin to that of Otsuka, Arima, and Iachello introduced in connection with the interacting boson model, but is more rigorous, general, and systematic.

Evaporative ${}_{}{}^{1,2,3}{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ yields and energy spectra have been analyzed in the framework of the statistical model in ten heavy-ion reactions, spanning composite systems with 20<Z<56. Transmission coefficients derived from the ingoing-wave boundary condition (IWBCM) or optical models (OM) have been used in the calculations. The effect of using different values of deformation parameters, level-density parameter a and radii of the real part of the transmission coefficient potentials has been investigated. Except for the low-energy side of the proton spectra, the shape of energy spectra are reasonably well reproduced by both sets of transmission coefficients. While the two models are essentially equivalent for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ cross sections, they differ significantly in the prediction of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ cross sections. OM transmission coefficients fail in reproducing ${}_{}{}^{2,3}{}_{}{}^{}\mathrm{H}$ cross sections, unless no standard parameters are used, while IWBCM transmission coefficients provide a good overall agreement. The failure of the OM is ascribed to the inclusion of nonfusion reactions in the inverse process.

Cross sections have been measured for the inelastic scattering of ${\mathrm{\pi }}^{+}$ and ${\mathrm{\pi }}^{\mathrm{-}}$ mesons from ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in the 10-MeV interval just above the breakup thresholds, for incident pion energies of 142, 180, and 220 MeV and scattering angles of 40°, 60°, 80°, 90°, and 110°. No significant departure from unity is observed for the ratios of charge-symmetric cross sections. Comparisons are made with elastic pion-scattering and inelastic electron-scattering data.

Double-differential proton emission cross sections have been measured for proton-induced reactions on ${}_{}{}^{98}{}_{}{}^{}\mathrm{Mo}$ and ${}_{}{}^{106}{}_{}{}^{}\mathrm{Pd}$ at incident energies around 26 MeV. Several sets of (p,p’) and (p,n) data for both target nuclei at incident energies from 12 to 26 MeV are analyzed in terms of the multistep-direct (MSD) and multistep-compound (MSC) reaction models of Feshbach, Kerman, and Koonin (FKK). The strength ${\mathit{V}}_0$ of the effective N-N interaction is extracted from a fit of the calculated MSD spectrum to the experimental data using the subtraction method of isolating and analyzing the MSD component alone. A similar analysis is also applied to (p,p’) and (n,n’) data for ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ in the same energy region. The experimental nucleon emission spectra at 26 MeV are reproduced well by the calculation that includes preequilibrium MSD and MSC emission, direct collective excitation to low-lying discrete levels, and Hauser-Feshbach equilibrium emission in a quantum-mechanical way. The systematic dependence of ${\mathit{V}}_0$ on the incident energy and the nature of projectiles and ejectiles is investigated. In addition, the sensitivities to input parameters used in the MSD calculation (the optical model potential parameters, the pairing correction, and the nonlocality correction) are examined in order to see their effect on the determination of ${\mathit{V}}_0$. The possibility of gradual absorption of reaction flux from the P to the Q chain is also discussed through analyses of preequilibrium (p,p’) and (p,n) spectra using a phenomenological phase space approach.

Binary fragmentations of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{209}$Bi (${\mathit{E}}_{\mathit{p}}$=491 MeV) and ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$${+}^{165}$Ho (${\mathit{E}}_{\mathit{p}}$=778 MeV) leading to compound nuclei with ${\mathit{E}}^{\mathrm{*}}$≊400 MeV and similar masses were investigated by measuring fission coincident neutrons and α particles. The neutron field was decomposed into contributions from preequilibrium (PE), prescission, and the two fragment sources with a moving source analysis. It was performed for separate excitation energy classes deduced with the folding angle technique from the linear momentum transfer. The angular distribution of the PE neutrons from the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{209}$Bi reaction indicates a pronounced out-of-plane anisotropy that would result in an overestimation of the PE multiplicity by 37% for a measurement only in plane. The PE multiplicities and temperatures are interpreted by a delay in formation for the more symmetric entrance channel ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$${+}^{165}$Ho, which is typical for quasifission and in line with the enhancement of asymmetric mass splits. Prescission times derived from the neutron clock method extend from 30×${10}^{\mathrm{-}22}$ s for ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$${+}^{165}$Ho to 160×${10}^{\mathrm{-}22}$ s for ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{209}$Bi. Here, a constant level density parameter of A/10 ${\mathrm{MeV}}^{\mathrm{-}1}$ was used which is an outcome of the simultaneous measurement of α emission temperatures. The prescission times are qualitatively discussed in terms of the reaction dynamics.

Discrete states in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ up to 25 MeV of excitation were studied by inelastic electron scattering. The measurements were performed at the Bates Linear Accelrator Center at 110° and 140°, and at momentum transfers ranging from about 1.2 to 2.5 ${\mathrm{fm}}^{\mathrm{-}1}$. A number of the states discussed here have not been observed previously. Form-factor measuremetns are presented for eight $4^{\mathrm{-}}$ candidates and for two $6^{\mathrm{-}}$ candidates. The strongest $4^{\mathrm{-}}$ state has T=2 and was observed at 22.40 MeV. Good T=2 $4^{\mathrm{-}}$ candidates were found at 18.68 and 20.36 MeV, and good T=1 $4^{\mathrm{-}}$ candidates were found at 8.52 and 12.99 MeV; the strongest $6^{\mathrm{-}}$ candidate was found at 14.17 MeV. Form-factor measurements are also presented for several $2^{\mathrm{-}}$ candidates. The M2 form factor for the lowest $2^{\mathrm{-}}$ state at 5.53 MeV is similar in shape to that for the lowest $2^{\mathrm{-}}$ state in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, but is weaker in strength. Finally, form-factor measurements are presented for several high-lying normal-parity states, including strong excitations at 9.36, 9.71, 11.67, and 17.02 MeV.

Experimental data on the nuclear spin-isospin response in the quasifree region, measured with the charge-exchange reaction (d→,2p${[}^1$${\mathit{S}}_0$]) at Laboratoire National Saturne, are presented. The use of a tensor-polarized beam enables us to separate the tensor analyzing powers ${\mathit{T}}_{20}$ and ${\mathit{T}}_{22}$. The present publication is intended to serve as a compilation of the complete set of quasifree data with the (d→${,}^2$He) reaction at 1.6 GeV bombarding energy. Data for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ are compared to calculated cross sections and tensor-analyzing powers. The cross section in the high-energy end of the quasielastic peak is underestimated, whereas the polarization observables are reasonably well reproduced. The distortion effects are, however, found to be large, suggesting that the (d→${,}^2$He) reaction is not sensitive to spin correlations in the continuum.

A differentially pumped windowless ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ gas target and a ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ beam produced with the ATLAS accelerator at Argonne National Laboratory were used to measure angle-averaged excitation functions for binary decay of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$${+}^{20}$Ne into low-lying states of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$${+}^{20}$Ne and ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{16}$O, in the region of excitation energy in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ from 51.4 to 58.2 MeV ${(}^{20}$Ne beam energies from 61.8 to 75.4 MeV). The ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$${+}^{20}$Ne mass partition displays little correlated structure and there exists no evidence of intermediate width resonances in these channels with branching ratios comparable to those seen in the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{24}$Mg system. Angular distributions for the elastic channel are consistent with those obtained using optical-model calculations. The exictation functions for the low-lying channels in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{16}$O do contain some structures, with widths varying from 400 to 800 keV in the c.m. system.

The ${}_{}{}^{12}{}_{}{}^{}$C(γ,pn) and ${}_{}{}^{12}{}_{}{}^{}$C(γ,pp) reactions have been measured for photon energies between 80 and 157 MeV using a photon tagging spectrometer and plastic scintillator detectors. The overall energy resolution was ∼7 MeV, sufficient to determine the initial shells of the emitted nucleons. Corrections were made for solid angle and threshold effects by means of Monte Carlo simulations. For the (γ,pn) reaction both the missing energy and recoil momentum distributions are largely consistent with a two-nucleon absorption process on p-shell an sp nucleon pairs. For the much smaller ${}_{}{}^{12}{}_{}{}^{}$C(γ,pp) cross section the reaction mechanism is not yet understood but the recoil momentum distributions suggest that final state interactions are not dominant.

Resonances in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ collisions have been studied for excitation of the 9.64-MeV $3^{\mathrm{-}}$ state. The alignment is large and nearly constant with energy, similar to other heavy ion collisions exciting weakly coupled states but unlike excitation of the strongly coupled 4.4-MeV $2^{+}$ state which shows a fluctuating alignment. It is concluded that the alignment behavior is determined by the coupling to the state excited rather than the particular heavy ion collision which excites the state.

The ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(γ,p${)}^{11}$B differential cross section has been measured over proton angles ranging from 58° to 128°, using tagged photons of energy 80–157 MeV, for low-lying regions of residual excitation energy in ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$. The data have been compared with four different types of calculation. It is shown that scaling of the cross section with momentum mismatch occurs for both the ground-state and excited-state data.

Total cross sections for incomplete fusion followed by fission have been measured for the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{232}$Th at 140 MeV. In-plane and out-of-plane measurements were made of cross sections for beamlike fragments in coincidence with fission fragments. The beamlike fragments were detected with a Bragg curve spectrometer which is position sensitive in the polar direction. The beamlike particles observed in coincidence with fission fragments were He, Li, Be, B, C, N, and O. One fission fragment from each reaction was detected by one of three surface barrier detectors using time of flight for particle identification. The measured cross section due to fission following incomplete fusion is 747±112 mb, or 42% of the total fission cross section. The strongest incomplete fusion channels were the He and C channels. The average transferred angular momentum for each incomplete fusion channel was predicted using the ${\mathit{Q}}_{\mathrm{opt}}$ model of Wilczyński so that the K distribution could be estimated from the rotating liquid drop model. The experimental angular distributions were fitted using the saddle point transition state model, with the transferred angular momentum J and the dealignment factor ${\mathrm{\alpha }}_0$ as free parameters. The saddle-point transition state model is found to adequately describe the observed angular correlations for fission following incomplete fusion. The fitted parameter J showed systematic deviations from the ${\mathit{Q}}_{\mathrm{opt}}$ model predictions, suggesting that the average impact parameter is larger than expected for heavy projectile fragments.

We have studied the core-polarization effects in pion elastic scattering from polarized ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$. The pion-nucleus spin-flip amplitude has been calculated within a framework of distorted-wave impulse approximation. To calculate the nuclear form factors we have used the wave function including the first-order core polarization with the intermediate states with excitation energies up to 12ħω. It is shown that the core-polarization effects reduce the absolute values of the asymmetry.

It is shown by way of a simplified model that the calculation of the time nonlocal potential resulting from an energy-dependent optical potential is not unique. Most choices result in a noncausal time-dependent potential, in spite of the inclusion of appropriate scattering boundary conditions in the model. Similarly, potentials arising from the many-body treatment of the optical potential are typically noncausal. However, it is demonstrated that, because of the energy spectrum of the Hamiltonian, the appropriate wave equations for scattering and the wave-function solutions in both approaches are nevertheless causal.

A model is proposed for studying exotic cluster radioactivities. This model is general and realistic that one can test the actual main treatments of clustering and penetration phenomena in nuclear many-particle systems. A reliable and rather simple approximation derived in this model is found on the continuum hopping treatment of clustering and on an integral formalism of decay dynamics including resonance scattering effects. The half-life estimates are performed for experimentally detected cluster radioactivities and for the most interesting cases under the current experimental search.

We propose a series of experimental measurements of the exclusive (N,N’π) process on light nuclei. It is suggested that different physical effects can be isolated by the following procedures: (a) varying the incident energy of the projectile nucleon at fixed nuclear energy and momentum transfer; (b) measuring ratios of cross sections to different ${\mathit{T}}_{\mathit{z}}$ substates of the same final nuclear isotopic multiplet; and (c) comparing ratios of cross sections for high spin non-normal parity states to those of low spin normal parity states. We discuss each of these methods for comparing data, and show what physical information can be extracted with each method.

Nonrelativistic reduction of the S matrix for the quasifree electron scattering process A(e,e’p)A-1 is studied in order to understand the source of differences between nonrelativistic and relativistic models. We perform an effective Pauli reduction on the relativistic expression for the S matrix in the one-photon exchange approximation. The reduction is applied to the nucleon current only; the electrons are treated fully relativistically. An expansion of the amplitude results in a power series in the nuclear potentials. The series is found to converge rapidly only if the nuclear potentials are included in the nuclear current operator. The results can be cast in a form which reproduces the nonrelativistic amplitudes in the limit that the potentials are removed from the nuclear current operator. Large differences can be found between calculations which do and do not include the nuclear potentials in the different orders of the nuclear current operator. In the high missing momentum region we find that the nonrelativistic calculations with potentials included in the nuclear current up to second order give results which are close to those of the fully relativistic calculation. This behavior is an indication of the importance of the medium modifications of the nuclear currents in this model, which are naturally built into the relativistic treatment of the reaction.