Since very recently, experimental data for the energy dependence of the ${}^{233}\mathrm{Pa}(n,f)$ cross section are finally available. This has stimulated a new, self-consistent cross section evaluation for the system $n+{}^{233}\mathrm{Pa}$ in the incident neutron energy range $0.01–6\text{MeV}$. The results are quite different compared to earlier evaluation attempts. Since ${}^{233}\mathrm{Pa}$ is an important intermediary in the thorium based fuel cycle, its neutron reaction cross sections are key parameters in the modeling of future advanced reactor concepts.

Excited, nonyrast states in ${}^{162}\mathrm{Yb}$ were populated through ${\beta }^{+}∕ϵ$ decay and studied through off-beam, $\beta$-delayed $\gamma$-ray spectroscopy at the Yale moving tape collector. New coincidence data provided evidence for a substantial revision of the previous level scheme and the elimination of a previously reported first excited $0^{+}$ state. The revised level scheme of ${}^{162}\mathrm{Yb}$ is compared to the predictions of the X(5) critical point symmetry. Good agreement is obtained for most energies while significant discrepancies exist with the current values of intraband $B\left(E2\right)$ values.

Dilute multi-$\alpha$ cluster condensed states with spherical and axially deformed shapes are studied with the Gross-Pitaevskii equation and Hill-Wheeler equation, where the $\alpha$ cluster is treated as a structureless boson. Applications to self-conjugate $4N$ nuclei show that the dilute $N\alpha$ states of ${}^{12}\mathrm{C}$ to ${}^{40}\mathrm{Ca}$ with $J^{\pi }=0^{+}$ appear in the energy region from threshold up to about $20\text{MeV}$, and the critical number of $\alpha$ bosons that the dilute $N\alpha$ system can sustain as a self-bound nucleus is estimated roughly to be $N_{cr}\sim 10$. We discuss the characteristics of the dilute $N\alpha$ states with emphasis on the $N$ dependence of their energies and rms radii.

Potential-model calculations for the energies and widths of $T=3∕2$ levels in $A=11$ nuclei have previously been used to argue that the $1∕2^{+},T=3∕2$ levels in ${}^{11}\mathrm{B}$ and ${}^{11}\mathrm{C}$ have been misidentified. Here we repeat these calculations using different, more reasonable, definitions for the energy and width of an unbound level, and also using a many-channel $R$-matrix model. We find reasonable agreement with the experimental energies of the $1∕2^{+},T=3∕2$ levels in ${}^{11}\mathrm{B}$ and ${}^{11}\mathrm{C}$ but possible disagreement in their widths.

We investigate reliability of Gamow-Teller transition strengths computed in the proton-neutron random phase approximation, comparing with exact results from diagonalization in full $0\hslash \omega$ shell-model spaces. By allowing the Hartree-Fock state to be deformed, we obtain good results for a wide variety of nuclides, even though we do not project onto good angular momentum. We suggest that deformation is as important or more so than pairing for Gamow-Teller transitions.

Spatial correlations in the three-body continuum of Borromean (having no bound binary subsystems) three-body systems are discussed. The hyperspherical harmonics method is used to investigate low-lying resonances and the soft dipole mode in the two-neutron halo nucleus ${}^6\mathrm{He}$, which has only the $\alpha +n+n$ continuum for excitation energies below $13\text{MeV}$. The spatial correlations reveal characteristic structures for true three-body resonances, a moderate amplification in the interior region for above-barrier resonances and long-range correlations in the cases of three-body $1^{-}$ virtual and $0^{+}$ continuum states.

Double folding model calculations to obtain the bare nucleus-nucleus potential have been carried out with the Reid and Paris M3Y effective nucleon-nucleon (NN) interactions. The exchange part of the interaction was taken to be of finite range and the density dependence of the NN interaction was accounted for. The calculated fusion barrier energies are generally lower than those expected taking into account potential renormalization due to coupling to collective states at high excitation energies. Fitting the potentials at the barrier radii with a Woods-Saxon form results in effective potential diffuseness of $\sim 0.65–0.70\text{fm}$, smaller than the values of $\sim 1\text{fm}$ generally found from fitting fusion cross sections at above-barrier energies. These discrepancies raise questions about both the determination of the bare nucleus-nucleus potential with the folding model, and the boundary of the effect of friction on the fusion process.

Existing data on near-barrier fusion excitation functions for 48 medium and heavy nucleus-nucleus systems have been analyzed using a simple “diffused-barrier formula” derived assuming the Gaussian shape of the barrier height distributions. The obtained mean values of the barrier height have been used then for determination of the parameters of the empirical nucleus-nucleus potential, assumed to have Woods-Saxon shape. The mean barrier heights calculated with this potential are reproduced with an accuracy of about $1\text{MeV}$, while other frequently used potentials, i.e., the proximity potential and the Akyüz-Winther potential, considerably overpredict the experimental values, especially for heavy systems. In order to predict fusion excitation functions with the diffused-barrier formula, we propose a simple method of theoretical prediction of the second parameter of the barrier distribution, its width. The proposed formula accounts for the quantum effect of sub-barrier tunneling, static quadrupole deformations, and collective surface vibrations of the colliding nuclei. With the theoretical knowledge of the mean height and width of the barrier distributions, one can predict cross sections for overcoming the barrier (“sticking” or “capture”) in reactions of very heavy systems used to produce superheavy nuclei.

A Si detector telescope, in which alternating thick and thin Si elements served as both targets and detectors, was used to measure the energy dependence of the inclusive one-proton-removal cross sections ${\sigma }_{1p}$ of ${}^8\mathrm{B}$, ${}^9\mathrm{C}$, and ${}^{12}\mathrm{C}$ on a Si target. A similar detector telescope was used to measure both ${\sigma }_{1p}$ and ${\sigma }_{2p}$ for ${}^9\mathrm{C}$; ${\sigma }_{2p}$ of ${}^9\mathrm{C}$ is more than twice as large as ${\sigma }_{1p}$ of ${}^9\mathrm{C}$ and almost as large as ${\sigma }_{1p}$ of ${}^8\mathrm{B}$. The measurements were compared with shell model calculations using eikonal reaction theory. The quenching factors $R_s$ (the ratio of the measurement to the theoretical prediction) for ${}^8\mathrm{B}$ and ${}^9\mathrm{C}$ were near unity, as at higher energies. They also agreed with those measured recently for those nuclei on a C target at $75\text{MeV}∕\text{nucleon}$. For ${}^{12}\mathrm{C}$ the quenching is greater with $R_s=0.44\pm 0.03$. This is comparable to the value $0.53\pm 0.02$ deduced at energies above $1\text{GeV}∕\text{nucleon}$.

Charge and mass distributions at $E_{lab}=114.4$ and $102.1\text{MeV}$, and the mass-resolved angular distribution at $E_{lab}=102.1\text{MeV}$ in ${}^{20}\mathrm{Ne}$ induced fission of ${}^{208}\mathrm{Pb}$ have been studied using the recoil catcher technique followed by off-line $\gamma$ ray spectrometry. The mass distributions have been found to be symmetric at both energies. The data on the variance of the mass distributions from this work and from literature have been analyzed to investigate the effect of the fissility on the stiffness of mass-asymmetric deformations. The stiffness was found to increase up to $Z^2∕A\sim 34$ and decrease at higher values of $Z^2∕A$. Angular anisotropies of 16 fission products have been measured. The results show that the angular anisotropy is not significantly correlated with the mass asymmetry. The experimentally determined angular anisotropy, averaged over the mass, was found to be significantly higher than that calculated using a statistical saddle point model.

We present a detailed study of chemical freeze-out in nucleus-nucleus collisions at beam energies of $11.6A$, $30A$, $40A$, $80A$, and $158A\text{GeV}$. By analyzing hadronic multiplicities within the statistical hadronization approach, we have studied the strangeness production as a function of center-of-mass energy and of the parameters of the source. We have tested and compared different versions of the statistical model, with special emphasis on possible explanations of the observed strangeness hadronic phase space undersaturation. We show that, in this energy range, the use of hadron yields at midrapidity instead of in full phase space artificially enhances strangeness production and could lead to incorrect conclusions as far as the occurrence of full chemical equilibrium is concerned. In addition to the basic model with an extra strange quark nonequilibrium parameter, we have tested three more schemes: a two-component model superimposing hadrons coming out of single nucleon-nucleon interactions to those emerging from large fireballs at equilibrium, a model with local strangeness neutrality and a model with strange and light quark nonequilibrium parameters. The behavior of the source parameters as a function of colliding system and collision energy is studied. The description of strangeness production entails a nonmonotonic energy dependence of strangeness saturation parameter ${\gamma }_S$ with a maximum around $30A\text{GeV}$. We also present predictions of the production rates of still unmeasured hadrons including the newly discovered ${\Theta }^{+}\left(1540\right)$ pentaquark baryon.

The properties of baryon resonances are extracted from a complicated process of fitting sophisticated, empirical models to data. The reliability of this process comes from the quality of data and the robustness of the models employed. With the large amount of data coming from recent experiments, this is an excellent time for a study of the model dependence of this extraction process. A test case is chosen where many theoretical details of the model are required, the $S_{11}$ partial wave. The properties of the two lowest $N^{*}$ resonances in this partial wave are determined using various models of the resonant and nonresonant amplitudes.

The mean last passage time is introduced instead of the mean first passage time for determining the decay rate of a nucleus after induced fission. The stationary fission rate calculated by the inverse of the mean last passage time at the saddle point is in agreement with the result of Langevin simulations and better than that of the mean first passing time at the scission point. In particular, we take into account the backstreaming effect where test particles pass over the potential barrier multiple times. It is shown that the oscillating time of a hot fissioning system around the saddle point is the longest one in time scales of the fission, thus more neutrons might be emitted during this period.

The radiative proton capture cross section to the $15.1\text{MeV}$ $T=1$ state in ${}^{12}\mathrm{C}$ has been measured in the reaction ${}^{11}\mathrm{B}\left(p,\gamma \right){}^{12}\mathrm{C}$ at the proton energies of $7.2\text{MeV}$ and $17–24\text{MeV}$ in $1\text{MeV}$ steps. The capture $\gamma$ ray was detected in coincidence with the $15.1\text{MeV}$ $\gamma$ ray arising from the subsequent decay of the $T=1$ state to the ground state. The measured cross sections, for $E_p=17–24\text{MeV}$, are much larger than the direct capture model prediction whereas the agreement with the model is good at $E_p=7.2\text{MeV}$. A semidirect capture model, including the excitation of the giant dipole resonance on the $15.1\text{MeV}$ state, reasonably explains the data. The energy and the width of the resonance are extracted.

A new model that includes the time-dependent dynamics of the single-particle motion in conjunction with the macroscopic evolution of the system is proposed for describing the compound nucleus formation in fusion of heavy nuclei. The diabaticity initially keeps the entrance system around its contact configuration, but the gradual transition from the diabatic to the adiabatic potential energy surface leads to fusion or quasifission. Direct measurements of the probability for compound nucleus formation are crucial to discriminate between the current models.

This work discusses the approximations frequently used to calculate the contribution to pion production in proton-proton scattering near threshold from irreducible pion rescattering. The reference result is obtained from the quantum-mechanical reduction of the corresponding Feynman diagram to time-ordered-field-theory diagrams. We conclude that the distorted wave Born approximation is quite adequate at threshold energies and even above. We discuss the choices for the energy of the exchanged pion, both for its propagator and for the $\pi N$ amplitude describing the rescattering vertex. The calculation employs a physical model for nucleons and pions—pseudovector coupling for the $\pi NN$ vertex and realistic amplitudes for the $\pi N$ rescattering and for the $NN$ transitions in the initial and final states.

Yrast transitions of the neutron deficient nucleus ${}^{93}\mathrm{Pd}$ were identified in the $\alpha n$ exit channel of the reaction ${}^{40}\mathrm{Ca}+{}^{58}\mathrm{Ni}$ at $135\text{MeV}$ using the gamma ray spectrometer GASP, the ISIS ball, and the $n$-ring detector system. The relationship of prompt $\gamma \gamma$ coincidences and the selection of $\gamma$ rays coincident with evaporated neutrons and $\alpha$ particles revealed for the first time the decay pattern of the high spin structure of the ${}^{93}\mathrm{Pd}$ nucleus. The spherical shell model calculations restricted to the $\pi ,\nu \left(p_{1∕2},g_{9∕2}\right)$ configuration space are in good accordance with the experimentally deduced level scheme of ${}^{93}\mathrm{Pd}$.

We study the decay of close to the spinodal metastable states through isobaric processes. One usually studies these processes by considering a Landau expansion of the free energy around the critical point, which may lie far away from the region of phase space where the dynamics are relevant, both in temperature and pressure. By relying on the critical nature of the spinodal points, apparent from the divergence of the compressibility and the presence of scaling in their vicinity, we propose an alternate view. By using, as a toy model, an analytical equation of state which describes a system that can exist in a liquid or vapor phase, we construct a generalized Gibbs-Landau free energy expansion around any spinodal point, which includes the critical point as a special case. This expansion is then used to study the dynamics of nucleation of the stable phase out of the metastable region.

The inclusive energy distributions of fragments $\left(4⩽Z⩽7\right)$ emitted in the reactions ${}^{16}\mathrm{O}\left(116\text{MeV}\right)+{}^{27}\mathrm{Al}$, ${}^{28}\mathrm{Si}$, ${}^{20}\mathrm{Ne}\left(145\text{MeV}\right)+{}^{27}\mathrm{Al}$, ${}^{59}\mathrm{Co}$ have been measured in the angular range ${\theta }_{lab}=10°–65°$. The respective fusion-fission and deep inelastic contributions have been decomposed from the experimental fragment energy spectra. The angular momentum dissipations in fully damped deep inelastic collisions have been estimated assuming exit channel configuration similar to those for fusion-fission process. It has been found that, the angular momentum dissipations are more than those predicted by the empirical sticking limit in all cases. The deviation is found to increase with increasing charge transfer (lighter fragments). Qualitatively, this may be due to stronger friction in the exit channel. Moreover, for the heavier system ${}^{20}\mathrm{Ne}+{}^{59}\mathrm{Co}$, the overall magnitude of deviation is less as compared to those for the lighter systems, i.e., ${}^{16}\mathrm{O}+{}^{27}\mathrm{Al}$, ${}^{28}\mathrm{Si}$, ${}^{20}\mathrm{Ne}+{}^{27}\mathrm{Al}$. This may be due to lesser overlap in time scales of fusion and deep inelastic time scales for heavier systems.

New experimental results for the cross section and $A_{yy}$ tensor analyzing power observables of the ${}^3\mathrm{He}\left(d,p\right){}^4\mathrm{He}$ reaction at a scattering angle of $\theta =0°$ are presented for $E_d=0.52,0.89,$ and $1.49\text{MeV}$, and all linearly independent scattering amplitudes at this angle are calculated. A hybrid $R\text{−}\text{matrix}+\text{potential}$ model is used to fit these results and other ${}^3\mathrm{He}\left(d,p\right){}^4\mathrm{He}$ reaction data for $E_d<1\text{MeV}$. This analysis indicates significant direct process contributions to the reaction mechanism.