Cross sections for single $\mathrm{}\left(1p\right)\mathrm{}$ and multinucleon ${(2p,}^4$He, and $p^4$He) transfer reactions have been measured in ${}^{19}$F, ${}^{16}$O, ${}^{12}$C+${}^{232}$Th systems at beam energies around the Coulomb barrier. Angular distributions and energy spectra of the projectilelike particles exhibit characteristics of direct transfer reactions. The ratio of the transfer to total reaction (transfer+fusion-fission) cross section is observed to be significantly smaller for the ${}^{12}$C projectile, as compared to that for ${}^{19}$F and ${}^{16}$O projectiles. All the systems show large transfer cross sections relative to the total reaction cross section at subbarrier energies. The angular distribution data were analyzed in terms of transfer probabilities to derive the slope parameter $\left(\alpha \right)$ for the stripping of $1p$ and $2p$ in the case of ${}^{16}$O and ${}^{12}$C projectiles and for $1p$, ${}^4$He and correlated ($p^4$He) stripping in the case of ${}^{19}$F projectile, for comparison with the semiclassical calculations. It is observed that the semiclassical picture is valid for $1p$ transfer at energies near the Coulomb barrier, whereas for correlated $2p$, ${}^4$He, and ($p^4$He) multinucleon transfers, the experimental values of $\alpha$ are anomalously small as compared to the semiclassical calculations even at subbarrier energies. At the above-barrier energies, the slope anomaly can be explained after inclusion of the nuclear effects in semiclassical calculations.

Measurements have been carried out for the fusion excitation function and one and two nucleon transfer probabilities at energies near and below the Coulomb barrier for the system ${}^{28}{\mathrm{S}\mathrm{i}+}^{93}\mathrm{Nb}.$ The recoil mass separator HIRA at the Nuclear Science Center, New Delhi, has been used for these measurements. A coupled-channels formalism has been employed for explaining the observed enhancement in the sub-barrier fusion cross section. Present results support the significance of positive $Q$-value transfer channel in the sub-barrier enhancement. The possible role of higher-order multiphonon coupling effects in the reaction mechanism have also been investigated.

The excitation functions have been measured for the ${}^{12}$C${(}^{12}$C,$\alpha )$${}^{20}$Ne and ${}^{12}$C${(}^{12}$C,${}^8$Be)${}^{16}$O reactions leading to the excited states up to 25 MeV in ${}^{20}$Ne and 20 MeV in ${}^{16}$O, respectively, in the beam energy range ${E(}^{12}$C)=48–72 MeV. The region of excitation investigated was $E_x$=38–50 MeV in ${}^{24}$Mg which is well above the threshold for breakup into six alpha particles. In the ${}^8$Be channel leading to the 6–7 MeV region of ${}^{16}$O, excitation functions were also measured for ${}^8$Be-$\gamma$ coincidences in ${}^{12}$C${(}^{12}$C,${}^8$Be)${}^{16}$O${}^{*}\to \gamma {+}^{16}$O${}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ particularly to distinguish between the otherwise unresolved 6.05 MeV, 0${}^{+}$ and 6.13 MeV, 3${}^{-}$ states in ${}^{16}$O. It is observed that a cluster of resonances in the excitation region 39–43 MeV in ${}^{24}$Mg decays via $\alpha$ and ${}^8$Be channels predominantly to the particle-hole states in ${}^{20}$Ne and ${}^{16}$O which are members of deformed bands. Another cluster of resonances in the region 44–49 MeV (centered at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=32.5 MeV) decays predominantly to the 20.48 MeV state in ${}^{20}$Ne (which is above the 5$\alpha$ breakup threshold) and to a possible 4$\alpha$ linear chain band in ${}^{16}$O around 18 MeV, indicating their highly deformed nature. This latter cluster structure coincides in energy with the possible 6$\alpha$ linear chain resonance identified in the literature at $E_{\mathrm{}\mathrm{c}.\mathrm{m}.\mathrm{}}$=32.5 MeV in the inelastic scattering channels ${}^{12}$C${}_{{7.65,0}^{+}}{+}^{12}$C${}_{{7.65,0}^{+}}$ and ${}^{12}$C${}_{{7.65,0}^{+}}{+}^{12}$C${}_{{9.64,3}^{-}}$. In this excitation energy region intermediate structures in the ${}^8$Be channel are found at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=31.5 and 33.5 MeV decaying to the 6.13 MeV, 3${}^{-}$ state and at $E_{\mathrm{}\mathrm{c}.\mathrm{m}.\mathrm{}}$=32.5 MeV decaying to the 6.92/7.13 MeV states of ${}^{16}$O. Similar resonances in the same energy region in inelastic scattering channels ${}^{12}$C${}_{\mathrm{g}.\mathrm{s}}$+${}^{12}$C${}_{{9.64,3}^{-}}$ and ${}^{12}$C${}_{\mathrm{g}.\mathrm{s}.\mathrm{}}{+}^{12}$C${}_{{7.65,0}^{+}}$ have also been reported in the literature. It is conjectured from the present measurements that in this region of excitation in ${}^{24}$Mg (44–49 MeV) there are at least two types of states excited in the collision of ${}^{12}$C+${}^{12}$C. The first type consists of 6$\alpha$ cluster resonances, possibly with large deformation, leading to outgoing channels above the breakup threshold into constituent alpha particles in both the products and the other type leading to outgoing channels below this threshold.

Angle averaged cross sections for the mutual excitation of the $0_2^{+},$ 6.05 MeV excited state of ${}^{16}\mathrm{O}$ have been measured over the center of mass energy region 30.0–43.5 MeV in steps of 200–400 keV. The excitation function is dominated by three wide structures centered at center of mass energies 33.0, 37.0, and 40.5 MeV. A spin assignment for an angular distribution measurement at 37.0 indicates the dominant spins of this exit channel are smaller than the spins that dominate the resonances observed in the single excitation to the $0_2^{+},$ 6.05 MeV excited state of ${}^{16}\mathrm{O}$ at comparable center of mass energies. This result is consistent with preliminary coupled channel calculations.

Two nucleon transfer reactions have been used to probe for correlations in nuclei but there have been doubts about the assumptions made and hence about the success of the analyses. An experimental study of the ${}^{40}\mathrm{Ca}{\mathrm{}(t,p)\mathrm{}}^{42}\mathrm{Ca}$ reaction at incident triton energies of 10–15 MeV/nucleon was made to determine if the one-step, two-nucleon transfer mechanism was dominant at these energies. Measurements were made with 28, 33, and 37.3 MeV incident energy and particular care was taken to measure absolute differential cross sections for transitions to several residual states in ${}^{42}\mathrm{Ca}.$ The analysis of all the data used the results of full finite-range calculations and care was taken to calculate all the one-step and two-step reaction channels in a consistent manner starting from a shell-model description of the relevant Ca isotopes with a single, large basis set of single-particle wave functions. Although a complete prediction of the data was not achieved, it is concluded that incident triton energies about 10 MeV/nucleon are still not enough for one-step, two-nucleon transfer to dominate the $\mathrm{}(t,p)\mathrm{}$ reaction mechanism. Even with a full analysis, it was not possible to reliably extract the reaction amplitudes by fitting the data because of the effects of the discrete potential ambiguity when describing elastic scattering. Hence it is not possible to extract accurate data about two-nucleon correlations in nuclei from $\mathrm{}(t,p)\mathrm{}$ reactions at these energies. Additionally, some measurements on the ${}^8\mathrm{Ca}{\mathrm{}(t,p)\mathrm{}}^{50}\mathrm{Ca}$ reaction with 37.3 MeV incident energy are presented. Using a similar analysis, calculations predicted the magnitude of the differential cross-section data and the structure of the angular distributions. The $J^{\pi }$ of the second excited state of ${}^{49}\mathrm{Ca}$ was shown to be ${7/2}^{-}.$

Isotopically resolved intermediate-mass fragments and light charged particles have been detected from the reactions ${}^{40}\mathrm{Ar}$ and ${}^{40}\mathrm{Ca}$ with ${}^{58}\mathrm{Fe}$ and ${}^{58}\mathrm{Ni}$ at $E_{\mathrm{beam}}=33\mathrm{}$ and 45 MeV/nucleon. There is an angular dependence to the isotopic ratios. A moving source analysis shows that fragments emitted at ${\Theta }_{\mathrm{lab}}=40\mathrm{}°$ can be attributed primarily to a composite source while the fragments emitted at backward angles are primarily from a targetlike source. The results are compared to predictions of QMD, BUU, and GEMINI. QMD generally reproduces the charge distribution and energy spectra and has partial success with the isobaric ratios when the system is chemically equilibrated. All of the models have difficulty reproducing the isotopic ratios when the system is not chemically equilibrated.

The ${(}^3$He,$p)$ reaction has been studied on ${}^{62}$Ni using a beam of 18 MeV ${}^3$He particles. Angular distributions of the outgoing protons have been measured for 65 levels including the new levels at 2.323, 3.231, 5.043, and 7.339 MeV and the analog states at 6.821 MeV ${(0\mathrm{}}^{+}$;4) and 8.188 MeV ${(2\mathrm{}}^{+};4)$ in the angular range ${\theta }_{\mathrm{lab}}=5\mathrm{}°$–80$°$. Data have been analyzed in terms of the distorted-wave Born approximation (DWBA). The $L$ transfers have been obtained, $J^{\pi }$ limits have been assigned, and the normalization constant has been deduced for several low-lying states.

The azimuthal distribution and azimuthal correlation of the emitted light charge particles in coincidence with the forward-going heavy fragments in the reaction of 10.6 MeV/nucleon ${}^{84}\mathrm{Kr}$ on ${}^{27}\mathrm{Al}$ have been studied in detail. A novel way to extract the reaction plane dispersion by combining the azimuthal distribution constructed using the experimental measured reaction plane which contains a reaction plane dispersion and a two-particle azimuthal correlation which is free of reaction plane dispersion was described. This method was applied to the low-energy fission reaction ${}^{84}\mathrm{Kr}$+${}^{27}\mathrm{Al}$ at 10.6 MeV/nucleon for light particles, $p$ and $\alpha$, with success.

Characteristics of charged-particle emission in heavy-ion reactions have been studied in the framework of the semiclassical Landau-Vlasov approach for the ${}^{40}$Ar + ${}^{27}$Al collisions at 65 MeV/nucleon. At all impact parameters, the reaction mechanism is dominated by binary dissipative collisions. After an abundant prompt emission coming from the overlapping region between the target and the projectile, two excited nuclei, the quasitarget and the quasiprojectile, emerge from the collision. To shed some light on the role played by dynamical effects, light charged-particle observables, which are currently used as an experimental signature of a hot equilibrated nucleus, have been carefully investigated. The model calculations show that binary dissipative collisions are closely related to the so-called participant-spectator scenario in which the “spectators,” identified as the quasitarget and the quasiprojectile, are not very hot.

The ${}^2\mathrm{H}\mathrm{}(p,n)\mathrm{}$ charge exchange reaction at $T_p=790\mathrm{}\mathrm{MeV}$ is used to study the Δ(1232)-nucleon $\left(\Delta N\right)$ interaction in the Δ resonance excitation energy region. For the $\Delta N$ potential, a meson exchange model is adopted where π, ρ, ω, and σ meson exchanges are taken into account. The deuteron disintegration below and above pion threshold is calculated using a coupled-channel approach. Various observables, such as the inclusive cross section, the quasifree Δ decay, the coherent pion production, and the two-nucleon breakup, are considered. It is shown that these observables are influenced by the dynamical treatment of the Δ degrees of freedom. Of special interest is the coherent pion decay of the Δ resonance, which is studied by means of the exclusive reaction ${}^2\mathrm{H}(p,n{\pi }^{+}{)}^2\mathrm{H}.$ Both the peak energy and the magnitude of the coherent pion production cross section depend very sensitively on the strength of the $\Delta N$ potential. The coherent pions have a peak energy of $\omega =300\mathrm{}\mathrm{MeV}$ and a strongly forward peaked angular distribution.

A wave-function framework for the theory of the ${(e,e}^{\prime }N)$ reaction is presented in order to justify the use of coupled channel equations in the usual Feynman matrix element. The overall wave function containing the electron and nucleon coordinates is expanded in a basis set of eigenstates of the nuclear Hamiltonian, which contain both bound states as well as continuum states. The latter have an ingoing nucleon with a variable momentum $Q$ incident on the daughter nucleus as a target, with as many outgoing channels as desirable. The Dirac equations for the electron part of the wave function acquire inhomogeneous terms, and require the use of distorted electron Green's functions for their solutions. The condition that the asymptotic wave function contains only the appropriate momentum $Q_k$ for the outgoing nucleon, which corresponds to the electron momentum $k$ through energy conservation, is achieved through the use of the steepest descent saddle point method, commonly used in three-body calculations.

Based on an effective field theory of hadrons in which quantum chromodynamics is assumed to provide the necessary bare cutoff functions, a gauge-invariant theory of pion photoproduction with fully dressed nucleons is developed. The formalism provides consistent dynamical descriptions of $\pi N\to \pi N$ scattering and $\gamma N\to \pi N$ production mechanisms in terms of nonlinear integral equations for fully dressed hadrons. Defining electromagnetic currents via the gauging of hadronic $n$-point Green's functions, dynamically detailed currents for dressed nucleons are introduced. The dressed hadron currents and the pion photoproduction current are explicitly shown to satisfy gauge invariance in a self-consistent manner. Approximations are discussed that make the nonlinear formalism manageable in practice and yet preserve gauge invariance. This is achieved by recasting the gauge conditions for all contributing interaction currents as continuity equations with “surface” terms for the individual particle legs coming into or going out of the hadronic interaction region. General procedures are given that approximate any type of (global) interaction current in a gauge-invariance-preserving manner as a sum of single-particle “surface” currents. It is argued that these prescriptions carry over to other reactions, irrespective of the number or type of contributing hadrons or hadronic systems.

An overall view on the universe of primary decays appearing in the process of nuclear multifragmentation via a microcanonical Monte Carlo Metropolis type simulation is given. General characteristics like mass and charge distributions, relative probabilities of evaporation, fission, fragmentation and vaporization, average number of fragments and distributions of a number of intermediate mass fragments offer valuable information about the intimacy of the process. The capability of the model to describe unitary very different breakup regimes is pointed out. Predictions for charge distributions, isotopic yields, and fission mass distributions are compared with experimental data.

The cross section and analyzing power of the $p\to p\to \mathrm{pn}{\pi }^{+}$ reaction near threshold are estimated in terms of data obtained from the $p\to p\to d{\pi }^{+}$ and $\mathrm{pp}\to \mathrm{pp}{\pi }^0$ reactions. A simple final state interaction theory is developed which depends weakly upon the form of the pion-production operator and includes some Coulomb corrections. Within the uncertainties of the model and the input data, the approach reproduces well the measured energy dependence of the total cross section and the proton analyzing power at a fixed pion center-of-mass angle of $90°$, from threshold to $T_p=330\mathrm{}$ MeV. The variation of the differential cross section with pion angle is also very encouraging.

A new method is described to deduce observables from the yields measured in a nuclear physics experiment with polarized beam and target. The method makes use of a formalism, known in the mathematical literature under the name of “diagonal scaling” or “biproportional matrix adjustment,” which deals with the problem of scaling the rows and columns of a matrix to obtain a new matrix with given row and column sums.

Optical model potentials for elastic nucleon-nucleus scattering are calculated for a number of target nuclides from a full-folding integral of two different realistic target density matrices together with full off-shell nucleon-nucleon $t$ matrices derived from two different Bonn meson exchange models. Elastic proton and neutron scattering observables calculated from these full-folding optical potentials are compared to those obtained from “optimum factorized” approximations in the energy regime between 80 and 400 MeV projectile energy. The optimum factorized form is found to provide a good approximation to elastic scattering observables obtained from the full-folding optical potentials, although the potentials differ somewhat in the structure of their nonlocality.

The angular distribution of differential cross sections for α and ${}^3\mathrm{He}$ projectiles elastically scattered from ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ are calculated at the energy range from 25 to 217 MeV. The double folding model with an energy-target density dependent Jeukenne, Lejeune, and Mahaux effective nucleon-nucleon interaction is used to obtain both real and imaginary parts of the central optical potential. The dependence of the potential on densities of projectile and target nuclei in a factorized form is considered. Good fits to the experimental data are obtained. Nuclear rainbow scattering is also observed and discussed.

An eigenchannel approach to heavy-ion fusion reactions is exact only when the excitation energy of the intrinsic motion is zero. In order to take into account effects of finite excitation energy, we introduce an energy dependence to weight factors in the eigenchannel approximation. Using the two channel problem, we show that the weight factors are slowly changing functions of incident energy. This suggests that the concept of the fusion barrier distribution still holds to a good approximation even when the excitation energy of the intrinsic motion is finite. A transition to the adiabatic tunneling, where the coupling leads to a static potential renormalization, is also discussed.

Using quantum molecular dynamics simulations, we investigate the formation of fragments in symmetric reactions between beam energies of $E=30A\mathrm{MeV}$ and $600A\mathrm{MeV}.$ After a comparison with existing data we investigate some observables relevant to tackle equilibration: $d\sigma {/dE}_{\mathrm{rat}},$ the double differential cross section $d^2\sigma {/p}_t{\mathrm{dp}}_z{\mathrm{dp}}_t,\dots .$ Apart maybe from very energetic $(E>~400A\mathrm{MeV})$ and very central reactions, none of our simulations gives evidence that the system passes through a state of equilibrium. Later, we address the production mechanisms and find that, whatever the energy, nucleons finally entrained in a fragment exhibit strong initial-final state correlations, in coordinate as well as in momentum space. At high energy those correlations resemble the ones obtained in the participant-spectator model. At low energy the correlations are equally strong, but more complicated; they are a consequence of the Pauli blocking of the nucleon-nucleon collisions, the geometry, and the excitation energy. Studying a second set of time-dependent variables (radii, densities, etc.), we investigate in detail how those correlations survive the reaction, especially in central reactions where the nucleons have to pass through the whole system. It appears that some fragments are made of nucleons which were initially correlated, whereas others are formed by nucleons scattered during the reaction into the vicinity of a group of previously correlated nucleons.

In this work the β decay of a nucleus hosted in an atomic or a molecular system is considered. A formalism is derived that allows the calculation of the changes in the β spectrum that are caused by the Coulombic final-state interaction of the β electron (or positron) with all molecular electrons as well as nuclei. Explicit formulas are derived for the matrix elements occurring in a perturbational treatment up to the pure first-order correction term, and different approximations are discussed. The result obtained in this work is especially applicable to cases where the decaying nucleus is part of a molecular system. In contrast to previous works a complete partial-wave analysis of the interaction operator has been performed, and for the first time explicit results are derived for all partial waves. The total symmetric contribution agrees (for atoms) with previous results and confirms the early work of Rose. However, the nonspherical contributions are of the same order of magnitude as the total symmetric contribution and have therefore to be taken into account, if the Rose correction is applied. This can be done in a very simple way, since the correction turns out to be (approximately) proportional to the number of electrons but otherwise completely independent of the atomic or molecular system under consideration. In the case of molecular systems also the contribution of the spectator nuclei has to be considered, since this contribution is again of the same order of magnitude as the correction term given by Rose. It is shown that the interaction with the decaying nucleus (that leads to the occurrence of the Fermi function) is very well approximated within the present perturbational approach, where it is treated in the same way as the interaction with the other particles.