Within the Cornwall-Jackiw-Tomboulis (CJT) approach a general formalism is established for the study of asymmetric nuclear matter (ANM) described by the four-nucleon interactions. Restricting ourselves to the double-bubble approximation (DBA), we determine the bulk properties of ANM, in particular, the density dependence of the nuclear symmetry energy, which is in good agreement with data of recent analyses.

We investigate several Pb$(n,n^{\text{'}}\gamma$) and Ge$(n,n^{\text{'}}\gamma$) reactions. We measure γ-ray production from Pb$(n,n^{\text{'}}\gamma$) reactions that can be a significant background for double-β decay experiments which use lead as a massive inner shield. Particularly worrisome for Ge-based double-β decay experiments are the 2041-keV and 3062-keV γ rays produced via Pb$(n,n^{\text{'}}\gamma$). The former is very close to the ${}^{76}\mathrm{Ge}$ double-β decay endpoint energy and the latter has a double escape peak energy near the endpoint. We discuss the implications of these γ rays on past and future double-β decay experiments and estimate the cross section to excite the level that produces the 3062-keV γ ray. Excitation γ-ray lines from Ge$(n,n^{\text{'}}\gamma$) reactions are also observed. We consider the contribution of such backgrounds and their impact on the sensitivity of next-generation searches for neutrinoless double-β decay using enriched germanium detectors.

Precise thermal neutron capture γ-ray cross sections ${\sigma }_{\gamma }$ were measured for all elements with $Z=1\text{−}83,90$, and 92, except for He and Pm, at the Budapest Reactor. These data were evaluated with additional information from the literature to generate the Evaluated Gamma-ray Activation File (EGAF). Isotopic radiative neutron cross sections can be deduced from the total transition cross section feeding the ground state, ${\sigma }_0=\Sigma {\sigma }_{\gamma }(\mathrm{GS})$ if the decay scheme is complete. The EGAF file contains partial γ-ray cross sections for all stable palladium isotopes. None of these decay schemes are complete, although in each case transitions de-exciting low-lying levels are known. We have performed Monte Carlo simulations of the palladium thermal neutron capture decay schemes using the computer code DICEBOX. The simulated populations of low low-lying levels are normalized to the measured ${\sigma }_{\gamma }$ values from EGAF and the total radiative neutron cross section ${\sigma }_0$ is obtained. The ${\sigma }_0$ values derived for the palladium isotopes agree well with previous measurements and were in several cases more precise. Complementary use of γ-ray cross-section data and Monte Carlo calculations has proven effective in determining both the palladium total radiative cross sections and new nuclear structure information.

The value of the $N^{*}(1535)N\rho$ coupling constant $g_{N^{*}N\rho }$ derived from the $N^{*}(1535)\to N\rho \to N\pi \pi$ decay is compared with that deduced from the radiative decay $N^{*}(1535)\to N\gamma$ using the vector-meson-dominance model. On the basis of an effective Lagrangian approach, we show that the values of $g_{N^{*}N\rho }$ extracted from the available experimental data on the two decays are consistent, though the error bars are rather large.

The electron-capture (EC) decay rate of ${}^7\mathrm{Be}$ in metallic Cu host and the ${\beta }^{-}$-decay rate of ${}^{198}\mathrm{Au}$ in the host alloy Al-Au have been measured simultaneously at several temperatures, ranging from 0.350 K to 293 K. No difference of the half-life of ${}^{198}\mathrm{Au}$ between 12.5 K and 293 K is observed to a precision of 0.1%. By utilizing the special characteristics of our double-source assembly, possible geometrical effects that influence the individual rates could be eliminated. The ratio of ${}^7\mathrm{Be}$ to ${}^{198}\mathrm{Au}$ activity thus obtained also remains constant for this temperatures range to the experimental precision of $0.15\pm 0.16\%$. The resulting null temperature dependence is discussed in terms of the inadequacy of the often-used Debye-Hückel model for such measurements.

Results of an exact treatment of the pairing transition from harmonic vibration to deformed rotation are compared to the results of the recently introduced “critical point” description. The exact results provide a microscopic justification for the assumptions used to find relevant analytic solutions of the collective pairing Hamiltonian. The energies and transition intensities from the two approaches are found to be in close agreement. Comparison to available data on the Pb isotopes suggests that ${}^{208}\mathrm{Pb}$ is very close to the critical-point of the pairing phase transition.

The high-spin spectroscopy of neutron-rich ${}^{109}\mathrm{Ru}$ is studied by measuring the prompt γ rays from the spontaneous fission fragments of ${}^{252}\mathrm{Cf}$ with 102 Compton-suppressed Ge detectors in the Gammasphere detector array. Previous band structures are confirmed and the ground state band is extended. A positive parity band based on a 332.5 keV level is newly identified. This band is proposed as a single-neutron excitation band built on the $7/2^{+}[404]$ Nilsson orbital. Some band structural characteristics are discussed.

We have determined for the first time the partial-capture cross sections for discrete $\gamma$ rays from neutron capture by ${}^{18}\mathrm{O}$ to the $5/2^{+}$ground, $1/2^{+}$second, and $3/2^{+}$ first excited states in ${}^{19}\mathrm{O}$ at $10⩽E_n⩽80$ keV. The first two cross sections agree with the calculated ones based on a nonresonant direct $p$-wave capture by ${}^{18}\mathrm{O}$ within a factor of two. On the other hand, the cross section to the $3/2^{+}$ state with a three-particle $(d_{5/2}){}^3$configuration was found to be about 180 times larger than the calculated one. We discussed a possible origin of the large discrepancy by referring to recent results of ${}^{18}\mathrm{O}$($n,\gamma$)${}^{19}\mathrm{O}$ at thermal energy.

We study the spatial structure of four valence neutrons in the ground state of ${}^8\mathrm{He}$ and ${}^{18}\mathrm{C}$ nuclei using a core$+4n$ model. For this purpose, we employ a density-dependent contact interaction among the valence neutrons, and solve the five-body Hamiltonian in the Hartree-Fock-Bogoliubov (HFB) approximation. We show that two neutrons with the coupled spin of $S=0$ exhibit a strong dineutron correlation around the surface of these nuclei, whereas the correlation between the two dineutrons is much weaker. Our calculation indicates that the probability of the ($1p_{3/2}){}^4$ and [$(1p_{3/2}){}^2(p_{1/2}){}^2$] configurations in the ground state wave function of ${}^8\mathrm{He}$ nucleus is 34.9% and 23.7%, respectively. This is consistent with the recent experimental finding with the ${}^8\mathrm{He}$($p,t){}^6\mathrm{He}$ reaction, that is, the ground state wave function of ${}^8\mathrm{He}$ deviates significantly from the pure ($1p_{3/2}){}^4$ structure.

The α particle preformation in the even-even nuclei from ${}^{108}\mathrm{Te}$ to ${}^{294}$118 and the penetration probability have been studied. The isotopes from Pb to U have been firstly investigated since the experimental data allow us to extract the microscopic features for each element. The assault frequency has been estimated using classical methods and the penetration probability from tunneling through the Generalized Liquid Drop Model (GLDM) potential barrier. The preformation factor has been extracted from experimental α decay energies and half-lives. The shell closure effects play the key role in the α preformation. The more the nucleon number is close to the magic numbers, the more the formation of α cluster is difficult inside the mother nucleus. The penetration probabilities reflect that 126 is a neutron magic number. The penetration probability range is very large compared to that of the preformation factor. The penetration probability determines mainly the α decay half-life while the preformation factor allows us to obtain information on the nuclear structure. The study has been extended to the newly observed heaviest nuclei.

We report measurements of the cross-section and a complete set of polarization transfer coefficients for the ${}^3\mathrm{He}(p,n)$ reaction at a bombarding energy $T_p=346$ MeV and a reaction angle ${\theta }_{\mathrm{lab}}=0^{°}$. The data are compared with the corresponding free nucleon-nucleon values on the basis of the predominance of quasielastic scattering processes. Significant discrepancies have been observed in the polarization transfer $D_{\mathit{LL}}(0^{°})$, which are presumably the result of the three-proton $T=3/2$ resonance. The spin-parity of the resonance is estimated to be $1/2^{-}$, and the distribution is consistent with previous results obtained for the same reaction at $T_p=48.8$ MeV.

The thermodynamic properties of nuclei are studied in a mean-field model by using a Skryme interaction. Properties of two-component systems are investigated over the complete range of proton fraction from a system of pure neutrons to a system of only protons. Besides volume, symmetry, and Coulomb effects we also include momentum- or velocity-dependent forces. Applications of the results developed are then given and include nuclear mechanical and chemical instability and an associated liquid-gas phase transition in two-component systems. The velocity dependence leads to further changes in the coexistence curve and nuclear mechanical and chemical instability curves.

The decay of the ${}^{246}\mathrm{Bk}$${}^{*}$ nucleus, formed in entrance channel reactions ${}^{11}\mathrm{B}+{}^{235}\mathrm{U}$ and ${}^{14}\mathrm{N}+{}^{232}\mathrm{Th}$ at different incident energies, is studied by using the dynamical cluster-decay model (DCM) extended to include the deformations and orientations of nuclei. The main decay mode here is fission. The other (weaker) decay channels are the light particles evaporation ($A⩽4$) and intermediate mass fragments ($5⩽A⩽20$). All decay products are calculated as emissions of preformed clusters through the interaction barriers. The calculated fission cross sections ${\sigma }_{\mathrm{fiss}}$, taken as a sum of the energetically favored symmetric and near symmetric fragments ($A_{\mathrm{CN}}/2\pm 7$ and $A=106\text{−}110$ plus complementary fragments) show an excellent agreement with experimental data at all experimental incident c.m. energies for both reactions, except for the top three energies in the case of the ${}^{11}\mathrm{B}+{}^{235}\mathrm{U}$ reaction. The disagreement between the DCM calculations and data at higher incident c.m. energies for the ${}^{11}\mathrm{B}+{}^{235}\mathrm{U}$ entrance channel is associated with the presence of additional effects of noncompound, quasifission (qf) components, in contradiction with the measured anisotropy effects which indicate the other entrance channel ${}^{14}\mathrm{N}+{}^{232}\mathrm{Th}$ to contain the noncompound nucleus contribution. The prediction of two fission windows, the symmetric fission (SF) and near symmetric or heavy mass fragments (HMFs), suggests the presence of a fine structure of fission fragments, which also need an experimental verification. The only parameter of the model is the neck length parameter $▵R$ whose value is shown to depend strongly on limiting angular momentum, which in turn depends on the use of sticking or nonsticking moment of inertia for angular momentum effects.

The axial-vector coupling $g_A$ of a constituent quark is estimated from matching the constituent quark model to the operator product expansion in QCD in the limit of large number of colors under some assumptions. The obtained relation is $g_A\simeq \sqrt{7/11}\approx 0.80$, which is in agreement with the existing model estimates.

The measurement of the giant electric dipole resonance built on the isobaric analog state in the self-conjugate even-even nucleus ${}^{12}\mathrm{C}$ is reported covering a wide excitation energy range. This is done using the ${}^{11}\mathrm{B}$($p,\gamma$) reaction leading to the 15.1 MeV $T=1$ state in ${}^{12}\mathrm{C}$ over a proton energy range of 7 to 24.5 MeV. Two resonances of 1.3 and 2 MeV widths are observed at excitation energies of 24.4 and 28.8 MeV superimposed on a smoothly varying cross section. The γ transitions from both the resonances are assigned $E1$ multipolarity. The structured $T=0$ component of the $E1$ strength distribution is thus very different from that built on the first $T=1$ state in the neighboring nucleus ${}^{14}\mathrm{N}$ and those built on the ground states of ${}^{12}\mathrm{C}$ and ${}^{14}\mathrm{C}$.

The bound-state level structures of the ${}_{\Lambda }^{16}$O and ${}_{\Lambda }^{15}$N hypernuclei were studied by γ-ray spectroscopy using a germanium detector array (Hyperball) via the ${}^{16}\mathrm{O}$ ($K^{-},{\pi }^{-}\gamma$) reaction. A level scheme for ${}_{\Lambda }^{16}$O was determined from the observation of three γ-ray transitions from the doublet of states ($2^{-},1^{-}$) at $~6.7$ MeV to the ground-state doublet ($1^{-},0^{-}$). The ${}_{\Lambda }^{15}$N hypernuclei were produced via proton emission from unbound states in ${}_{\Lambda }^{16}$O. Three γ rays were observed, and the lifetime of the $1/2^{+};1$ state in ${}_{\Lambda }^{15}$N was measured by the Doppler shift attenuation method. By comparing the experimental results with shell-model calculations, the spin dependence of the $\Lambda N$ interaction is discussed. In particular, the measured ${}_{\Lambda }^{16}$O ground-state doublet spacing of $26.4\pm 1.6\pm 0.5$ keV determines a small but nonzero strength of the $\Lambda N$ tensor interaction.

We study the mechanisms that reduce the proton $1d_{3/2}\text{−}1d_{5/2}$ spin-orbit splitting and the neutron $1f_{7/2}$ subshell closure in ${}^{42}\mathrm{Si}$. We use various self-consistent mean-field models: nonrelativistic Skyrme-Hartree-Fock and relativistic density-dependent Hartree-Fock. Special attention is devoted to the influence of a tensor component in the effective interaction. It is found that the tensor force indeed governs the reduction of the $1d$ proton spin-orbit splitting. On the other hand, the reduction of the neutron $1f_{7/2}$ subshell closure is not clearly related to the tensor force.

New data were taken at the Triangle Universities Nuclear Laboratory to investigate the plausibility of using low energy deuterons and the ${}^{10}\mathrm{B}$$(d,n)$${}^{11}\mathrm{C}$ reaction as a portable source of 6.3 MeV neutrons. Analysis of the data at and below incident deuteron energies of 160 keV indicates an $n_0$ neutron cross section that is lower than previous estimates by at least three orders of magnitude. In separate runs, deuterons with two different energies (160 and 140 keV) were stopped in a ${}^{10}\mathrm{B}$ target. The resulting $n_0$ neutrons of approximately 6.3 MeV were detected at angles between $0^{°}$ and ${150}^{°}$. The angle integrated yields were used to determine the astrophysical $S$ factor for this reaction assuming a constant value for the $S$ factor below 160 keV. The cross sections reported between 130 and 160 keV were calculated using the extracted value of the $S$ factor. The measured $n_0$ cross section is several orders of magnitude smaller than previous results, thus eliminating ${}^{10}\mathrm{B}$$(d,n)$${}^{11}\mathrm{C}$ as a portable source of intense neutrons with low energy deuteron beams on the order of tens of microamps. In order to gain insight into the reaction dynamics at these low energies the cross section results have been compared with results from calculations using the distorted wave Born approximation (DWBA) and a detailed Hauser-Feshbach calculation performed by the authors. The angular distribution is consistent with the Hauser-Feshbach calculation suggesting a statistical compound nucleus reaction rather than a direct reaction.

Fusion data for ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ are analyzed by coupled-channels calculations. It is shown that the calculated cross sections are sensitive to the couplings to the $2^{+}$ and $3^{-}$ excitation channels even at low energies, where these channels are closed. The sensitivity to the ion-ion potential is investigated by applying a conventional Woods-Saxon potential and the M3Y+repulsion potential, consisting of the M3Y double-folding potential and a repulsive term that simulates the effect of the nuclear incompressibility. The best overall fit to the data is obtained with a M3Y+repulsion potential that produces a shallow potential in the entrance channel. The stepwise increase in measured fusion cross sections at high energies is also consistent with such a shallow potential. The steps are correlated with overcoming the barriers for the angular momenta $L=12,14,16$, and 18. To improve the fit to the low-energy data requires a shallower potential and this causes a even stronger hindrance of fusion at low energies. It is therefore difficult, based on the existing fusion data, to make an accurate extrapolation to energies that are of interest to astrophysics.

We develop the exit doorway model for elastic breakup of loosely bound projectiles. We argue that this model could, in principle, supply an alternative simplified version of the continuum discretized coupled-channels (CDCC) model. We show that the cross section for elastic breakup can be generally written as a product of the cross section for inelastic excitation times a factor containing the excitation energy and width of the exit doorway and is generally bombarding energy dependent. The excitation energy of the exit doorway is identified with the $Q$ value of the breakup channel. The width of the exit doorway is a measure of the energy range of the continuum that is discretized. We apply the theory to derive closed expressions for the nuclear breakup cross sections in the adiabatic limit using the Austern-Blair theory. We demonstrate the approximate validity of the scaling law that dictates that the nuclear breakup cross section scales linearly with the radius of the target. We also compare our results for the nuclear breakup cross section of ${}^{11}\mathrm{Be}$, ${}^8\mathrm{B}$, and ${}^7\mathrm{Be}$ on several targets with recent CDCC calculation.