We have carried out a computational comparison of all existing quantum-mechanical models for multistep direct (MSD) reactions. The various MSD models, including the so-called Feshbach-Kerman-Koonin, Tamura-Udagawa-Lenske and Nishioka-Yoshida-Weidenmüller models, have been implemented in a single computer system. All model calculations thus use the same set of parameters and the same numerical techniques; only one adjustable parameter is employed. The computational results have been compared with experimental energy spectra and angular distributions for several nuclear reactions, namely, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$(p,p’) at 80 MeV, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$(p,p’) at 62 MeV, and ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$(n,n’) at 25.7 MeV. In addition, the results have been compared with the Kalbach systematics and with semiclassical exciton model calculations. All quantum MSD models provide a good fit to the experimental data. In addition, they reproduce the systematics very well and are clearly better than semiclassical model calculations. We furthermore show that the calculated predictions do not differ very strongly between the various quantum MSD models, leading to the conclusion that the simplest MSD model (the Feshbach-Kerman-Koonin model) is adequate for the analysis of experimental data.

A unified description of scattering cross sections as well as bound and quasibound states for the systems α${+}^{16}$O and α${+}^{15}$N is presented. Optical potentials have been extracted from the analysis of elastic α-scattering data on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ in a wide range of energies. Special emphasis was given to the α${+}^{16}$O scattering at energies near the Coulomb barrier. The real part of the potential was calculated using the double-folding procedure. Effective nucleon-nucleon interactions with different density dependence as well as zero-range and finite-range knock-on-exchange potentials are investigated. The dispersive part of the real potential was calculated using the dispersion relation of the optical potential. Together with the dominating channel potential it reproduces the observed energy dependence of the volume integral of the real part of the potential. We calculate the energies and other properties of bound and resonance α-cluster states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and find good agreement with the experimental data. As an application of the derived energy dependence of the optical potential we calculate α${+}^{16}$O excitation functions in the energy range from 10 to 30 MeV. In this region strong resonances in the compound system are observed.

The contributions of right-handed weak currents in neutrinoless double beta decay are studied taking explicitly into account the mass corrections to the intermediate neutrino propagator. Due to these corrections the right-handed currents become effective even if all neutrinos are light (${\mathit{m}}_{\nu }$>10 MeV). Explicit expressions for the neutrino-momentum integrals and the decay half-life are derived. As an example two neutrino-mass scenarios containing the hypothetical 17-keV neutrino are discussed. The experimental half-life of the ${}_{}{}^{76}{}_{}{}^{}\to _{}^{76}{}_{}{}^{}$Se decay is used to obtain an upper limit for a new kind of effective right-handed coupling within the two scenarios.

We calculate the ${\mathrm{\chi }}^2$ of various NN potential models with respect to the pp scattering data. We find that only the potential models which were explicitly fitted to the pp data give a reasonable description of these data. Most models give a pretty large ${\mathrm{\chi }}^2$ on the very low-energy pp data, due to incorrect ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ phase shifts.

An analytic method of generating resonant state expansions from the standard completeness relation of nonrelativistic quantum mechanics is described and shown to reproduce the generalized completeness relations, earlier derived, involving resonant states. The method is then applied to the expansion of the resolvent (the complete Green’s function), the symmetry properties of which seem to be destroyed if a conventional application of the completeness relations is made. These forms of expansions have a continuum term which contains symmetry-restoring contributions and can therefore never vanish identically, nor can it be neglected. The symmetry-conserving form of the expansion has a set of discrete terms which are identical in form to those of the Mittag-Leffler series for the resolvent. In addition, it contains a continuum contribution which in some cases vanishes identically, but in general does not. We illustrate these findings with numerical applictions in which the potential (a square well) is chosen so as to permit analytic evaluation of practically all functions and quantities involved.

Results are presented for pion interferometry measurements of 1.2A GeV La+La at the Lawrence Berkeley Laboratory Heavy Ion Spectrometer System. The experiment’s acceptance is at forward angles in the center-of-mass system. The fit parameters R, τ, λ, ${\mathit{R}}_{\mathrm{\perp }}$, and ${\mathit{R}}_{\mathrm{\parallel }}$ are presented. The extracted shape of the pion source is oblate. The correlation between the extracted size of the pion source and the centrality of the collision is investigated as well as the dependence of the source size on the mean momentum of the pion pairs. We conclude that the fitted radius parameters scale with mass for symmetric systems. We observe a dependence of the fitted size of the pion source on the mean momentum of the pion pairs. Comparisons are made with previous results.

We extend the normal transport model to include the medium effect on pions by treating them as quasiparticles. The property of the quasipion is determined using the delta-hole model. Modeling heavy-ion collisions at intermediate energies with the new transport equations, we find that it leads to an enhanced production of pions with low kinetic energies. This gives a plausible explanation for the observed enhancement of soft pions in the Bevalac experiments.

Multipion correlations arising from the symmetrization of the n-pion wave function affect the extracted information from two-pion correlation measurements. The influence of multipion correlations on a sample of like-pion pairs can be expressed as a multipion correlation factor, the distribution of which offers good sensitivity to the multipion correlation effect. Analyses of the multipion correlation factor for two Bevalac streamer chamber data samples of 2.1A GeV Ne+Pb and 1.8A GeV Ar+Pb collisions show that the multipion correlation effect in the former sample is greater than in the latter. This result mainly arises from the fact that the pion source for Ne projectiles is smaller than for Ar projectiles. The residual correlations in the reference sample are related to the multipion correlation factor in multipion events, which can be expressed as a residual correlation factor. The influence of multipion correlations on two-pion interferometry analyses arises from the ratio of the residual correlation factor to the multipion correlation factor.

The expectation value of the θ term in QCD for nuclear matter is estimated in the nucleon gas approximation. There is no significant renormalization (to an accuracy ∼10%) of the CP violation in nuclei due to the similar behaviors for the in-medium values of the θ term and quark condensates.

Double beta decay of ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ has been confirmed and the ratio of half-lives for ββ decay of ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$ and ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ has been precisely determined as ${\mathit{T}}_{1/2}^{130}$/${\mathit{T}}_{1/2}^{128}$=(3.52±0.11)×${10}^{\mathrm{-}4}$ by ion-counting mass spectrometry of Xe in ancient Te ores, using techniques that reduce interferences due to trapped Xe. We have also detected excesses of ${}_{}{}^{126}{}_{}{}^{}\mathrm{Xe}$ originating in high energy reactions of cosmic ray muons and their secondaries on Te; such reactions make minor contributions to the measured ${}_{}{}^{128}{}_{}{}^{}\mathrm{Xe}$ excesses in the Te ores. The Xe measurements, combined with common Pb dating of the ores, yield a ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$ half-life of (2.7±0.1)×${10}^{21}$ yr and thus a ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ half-life of (7.7±0.4)×${10}^{24}$ yr, the longest radioactive decay lifetime measured to date. These results give limits on the effective Majorana mass of the neutrino (<1.1–1.5 eV) and right-handed currents (‖〈η〉‖<5.3×${10}^{\mathrm{-}8}$) comparable to the best obtained from direct neutrinoless ββ-decay searches. They also imply new limits on unconventional Majorons not constrained by measurements of the ${\mathit{Z}}^0$ decay width.

The parity-violating asymmetry A is calculated for quasielastic electron scattering. We use a relativistic mean field model of the nuclear matter response. A Lorentz scalar mean field (which reduces the nucleon’s mass) decreases ‖A‖ by a relatively large amount. This effect must be understood before information on strange quark contributions or weak axial currents can be extracted. Alternatively, very interesting information on isoscalar convection currents could be obtained.

In this paper we present a study of all spin-dependent observables (without observing the neutrinos), which are even under time reversal, for the $1^{+}$→$0^{+}$ ${\mathrm{\beta }}^{\pm }$ decay transitions. Terms of the hadronic response function up to order κ/M and ${\mathrm{\kappa }}^2$${\mathit{R}}^2$ in the momentum transfer κ are included. The completeness of the parametrization of the decay rates of the present approach is demonstrated. Albeit the results obtained in this paper contain a complete set of one-body weak current form factors (except for the scalar form factor ${\mathit{F}}_{\mathit{S}}$), particular attention is paid to the possible extraction of the induced pseudoscalar form factor ${\mathit{g}}_{\mathit{P}}$ from observables in which charged lepton polarizations are measured. The theoretical uncertainties and the experimental feasibility are studied to some extent. It is shown that ${\mathit{g}}_{\mathit{P}}$ can in principle be determined in precision β decay experiments where the charged lepton polarizations are measured.

We investigate in a unified way the reaction mechanism of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$${(}^3$H,n${)}^9$Be and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$${(}^3$He, p${)}^9$Be at the low energies ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$≤2 MeV of astrophysical interest. Assuming charge independence of the nuclear reaction amplitudes and taking account of the effects from different isospin contribution, Coulomb interaction, and associated kinematical conditions properly, we constrain the upper and lower bounds of the total cross section of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$${(}^3$H,n${)}^9$Be theoretically by using knowledge of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$${(}^3$He, p${)}^9$Be reaction. It is found that the total cross section of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$${(}^3$H,n${)}^9$Be at Gamow window energy E∼250 keV is dominated by the near-threshold T=1 resonance whose resonance parameters are not determined at all experimentally, although the direct reaction process makes progressively important contributions at higher energies 500 keV≤${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$. Primordial abundance of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ calculated in the inhomogeneous and standard big-bang models by using the inferred reaction cross section for ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$${(}^3$H,n${)}^9$Be is compared with recent results of astronomical observations.

The polarization transferred to ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$ in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p→${,}^{12}$N→)n reaction has been measured for ${\mathit{E}}_{\mathit{p}}$=120 and 150 MeV. The lower bound on the polarization transfer coefficient, ${\mathit{K}}_{\mathit{y}}^{\mathit{y}}$≥0.347±0.019, is in good agreement with measurements at ${\mathit{E}}_{\mathit{p}}$=50 and 72 MeV.

The (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$) reaction on ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ has been measured in the reaction plane at ${\mathit{T}}_{\mathrm{\pi }}^{+}$=280 MeV and the cross sections determined. The out of plane behavior of the reaction has been accounted for by phase space and, by integration over it, total cross sections have been deduced. Data are compared with the results of model calculations that, based on different approaches and approximations, predict total cross sections largely discordant. Finally, the analogy between the processes of pion production and double charge exchange is discussed in terms of total cross sections.

A second quasi-random-phase approximation (QRPA) procedure is employed to perform calculations of the ${\mathit{M}}_{\mathrm{GT}}^{2\nu }$ matrix elements for several ββ emitters. It is found that higher-order QRPA (HQRPA) corrections display a weak dependence on particle-particle (pp) strength ${\mathit{g}}_{\mathrm{pp}}$ and, in the physical region (around ${\mathit{g}}_{\mathrm{pp}}$=1.0), they become important by comparison with QRPA predictions. It turns out that a further investigation of the HQRPA corrections could be illuminating to obtain more stable and reliable values for ${\mathit{M}}_{\mathrm{GT}}^{2\nu }$ matrix elements in this region, where they are very sensitive to the pp strength.

Internal conversion coefficients (ICC’s) have been calculated for protactinium and transition energies between 170 eV and 10 keV. The ICC’s for E1 multipolarity show an unusual behavior, which cannot be approximated by an exponential dependence on the transition energy, whereas the ICC’s for M1 and E2 multipolarities closely follow such a dependence. Using the newly calculated ICC’s the unusually strong ‘‘enhancement’’ of a possible 220 eV E1 transition in ${}_{}{}^{229}{}_{}{}^{}\mathrm{Pa}$ proposed earlier is reduced by a factor of ∼5, yielding an induced electric dipole moment similar to that observed in the neighboring octupole-deformed isotopes.

We obtain the asymmetry parameter as a function of lepton energy for the scattering of polarized muons from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ in the inelastic process l${+}^{12}$C${\to }^{12}$${\mathrm{C}}^{\mathrm{*}}$+l’. Only the case for highly relativistic leptons is considered but ${\mathit{q}}^2$ is allowed to become small. It is found that the asymmetry parameter increases rapidly with decreasing ${\mathit{q}}^2$ at very small angles. The cases of the tau lepton as well as that of the low-energy electron are also considered.

After considering the vacuum polarization and the radiative correction of the nucleon-nucleon-pion (NNπ) system, the one-pion exchange potential with pseudovector coupling or pseudoscalar coupling at finite temperature and finite density is investigated. By using finite-temperature and density quantum field theory, we find that both the pseudovector and pseudoscalar effective coupling of NNπ decrease as temperature and/or density increase, and drop remarkably at high temperature regions and/or high density regions. At a critical temperature ${\mathit{T}}_{\mathit{c}}$ or a critical density ${\mathrm{\rho }}_{\mathit{c}}$, the effective NNπ coupling diminishes to zero and the one-pion exchange potential vanishes.

Detailed energy distributions have been calculated for exclusive ${\mathrm{\pi }}^0$ production in C+C collisions below and above threshold. The quantum-coherent, microscopic, many-body formalism used previously has been extended to include the ρ-exchange as well as the π-exchange interaction modified to produce nucleon isobars in the intermediate nuclear states. Analytic solutions to the Δ-hole and particle-hole coefficients using the degenerate, schematic-model approximation are used where collective-coherent, spin-isospin giant resonances are assumed for the nuclear excited states. The nuclear form factors that depend on these coefficients are solved analytically and become sums of degenerate Δ-hole and particle-hole states for given multipole angular momentum values of the excited nuclei. Also, in this approach, the overall amplitudes and differential cross sections for ${\mathrm{\pi }}^0$ production in either nucleus have been formally solved and the first numerical results of the pion, kinetic-energy distributions are presented.