The differential $\mathrm{np}$ scattering cross section has been measured at 96 MeV in the angular range ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=74\mathrm{}–180°$ at the neutron beam facility of the The Svedberg Laboratory in Uppsala. A subset of the data, covering $116–180°,$ has previously been published. The new, extended angular distribution has been normalized to the experimental total $\mathrm{np}$ cross section. Between 150° and $180°,$ the angular distribution is steeper than for most previous measurements and nucleon-nucleon potential predictions. At $180°,$ the difference amounts to about 10%, implying serious consequences because of the fundamental importance of this cross section. A value of the charged $\pi \mathrm{NN}$ coupling constant consistent with our earlier result at 162 MeV has been extracted from the data.

The quasiparticle representation of the phonon damping model (PDM) is developed to include the superfluid pairing correlations microscopically. The formalism is applied to calculate the photoabsorption and the electromagnetic (EM) differential cross sections of $E1\mathrm{}$ excitations in neutron-rich oxygen and calcium isotopes. The calculated photoabsorption cross sections agree reasonably well with the available data for ${}^{16,18}\mathrm{O}$ and ${}^{40,48}\mathrm{Ca}.$ The fractions of energy-weighted sum of strength in the region of the pygmy dipole resonance (PDR) ${(E}_{\gamma }<~15–16$ MeV) and the PDR peaks in the EM cross sections for ${}^{20,22}\mathrm{O}$ are also found in reasonable agreement with experimental systematics. The deviation from the prediction given by the cluster model’s sum rule shows the importance of the effect of coupling to noncollective degrees of freedom in the damping of pygmy and giant dipole resonances.

We have measured high-energy γ rays up to $E_{\gamma }=23\mathrm{}\mathrm{MeV}$ from three highly excited medium mass nuclei, ${}^{112}\mathrm{Sn},$ ${}^{131}\mathrm{La},$ and ${}^{134}\mathrm{Ce}.$ The absolute ${}^{131}\mathrm{La}$ γ-ray multiplicity has been compared to statistical model calculation without any normalization. We have found that level density prescriptions of Pülhofer and Ignatyuk-Smirenkin-Tishin–Reisdorf fit the data with giant dipole resonance centroid energy and width taken from systematics, whereas the experimental level density parameters of Budtz-Jørgensen and Knitter fail to fit the data.

We calculate the inclusive cross section for prompt photon production in heavy-ion collisions at RHIC energies $(\sqrt{s}=130\mathrm{}$ GeV and $\sqrt{s}=200\mathrm{}$ GeV) in the central rapidity region including next-to-leading order, $O\left({\alpha }_{\mathrm{em}}{\alpha }_s^2\right),$ radiative corrections, initial state nuclear shadowing, and parton energy loss effects. We show that there is a significant suppression of the nuclear cross section, up to ∼30% at $\sqrt{s}=200\mathrm{}$ GeV, due to shadowing and medium induced parton energy loss effects. We find that the next-to-leading order contributions are large and have a strong $p_t$ dependence.

Information on level density for nuclei with mass numbers $A\sim 20–250$ is deduced from discrete low-lying levels and neutron resonance data. The odd-mass nuclei exhibit in general 4–7 times the level density found for their neighboring even-even nuclei at the same excitation energy. This excess corresponds to an entropy of $\sim 1.7k_B$ for the odd particle. The value is approximately constant for all midshell nuclei and for all ground state spins. For these nuclei it is argued that the entropy scales with the number of particles not coupled in Cooper pairs. A simple model based on the canonical ensemble theory accounts qualitatively for the observed properties.

The isovector dipole response in ${}^{208}\mathrm{Pb}$ is described in the framework of a fully self-consistent relativistic random phase approximation. The NL3 parameter set for the effective mean-field Lagrangian with nonlinear meson self-interaction terms, used in the present calculations, reproduces ground state properties as well as the excitation energies of giant resonances in nuclei. In addition to the isovector dipole resonance in ${}^{208}\mathrm{Pb},$ the present analysis predicts the occurrence of low-lying $E1\mathrm{}$ peaks in the energy region between 7 and 11 MeV. In particular, a collective state has been identified whose dynamics correspond to that of a dipole pygmy resonance: the vibration of the excess neutrons against the inert core composed of an equal number of protons and neutrons.

The half-life of ${}^{37}\mathrm{Ar}$ has been determined via mass spectrometry by measuring the ratio of ${}^{37}\mathrm{Ar}$ to stable ${}^{36}\mathrm{Ar}$ as a function of time in neutron-irradiated samples of ${\mathrm{CaF}}_2.$ The half-life we obtain is $34.95\pm 0.08\mathrm{d}$ (95% confidence level). This result is compared to previous experiments based on radioactivity measurements.

Two models are presented for the description of the electron screening effects that appear in laboratory nuclear reactions at astrophysical energies. The two-electron screening energy of the first model agrees very well with the recent LUNA experimental result for the breakup reaction ${}^3\mathrm{He}{(}^3\mathrm{He}{,2p)}^4\mathrm{He},$ which so far defies all available theoretical models. Moreover, multielectron effects that enhance laboratory reactions of the CNO cycle and other advanced nuclear burning stages are also studied by means of the Thomas-Fermi model, deriving analytical formulas that establish a lower and upper limit for the associated screening energy. The results of the second model, which show a very satisfactory compatibility with the adiabatic approximation ones, are expected to be particularly useful in future experiments for a more accurate determination of the CNO astrophysical factors.

We investigate three models for the charge symmetry breaking (CSB) of the nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ interaction (based upon $\rho -\omega$ mixing, nucleon mass splitting, and phenomenology) that all reproduce the empirical value for the CSB of the ${}^1{S}_0$ scattering length $\left(\Delta a_{\mathrm{CSB}}\right)$ accurately. We reveal that these models make very different predictions for CSB in ${}^3{P}_J$ waves and examine the impact of this on some observable quantities of $A>~3$ nuclear systems. It turns out that the ${}^3\mathrm{H}{-}^3\mathrm{He}$ binding energy difference is essentially ruled by $\Delta a_{\mathrm{CSB}}$ and not very sensitive to CSB from P waves. However, the Coulomb displacement energies (which are the subject of the Nolen-Schiffer anomaly) receive about 50% of their CSB contribution from $\mathrm{NN}$ partial waves beyond ${}^1{S}_0.$ Consequently, the predictions by the various CSB models differ here substantially (10%–20%). Unfortunately, the evaluation of the leading Coulomb contributions carries a large uncertainty such that no discrimination between the competing CSB models can presently be made. To decide the issue we suggest looking into nuclear few-body reactions that are sensitive to CSB of the nuclear force.

Data for the inclusive process ${}^3\mathrm{He}\to \left(\overrightarrow{e}{,e}^{\prime }\right)$ have been theoretically analyzed and values for the magnetic and electric neutron form factors have been extracted at $Q^2=0.1\mathrm{}$ and 0.2 ${\mathrm{GeV}}^2{/c}^2.$ Similarly a theoretical analysis has been carried through for the process ${}^3\mathrm{He}\to \left(\overrightarrow{e}{,e}^{\prime }n\right)$ and the value of the electric neutron form factor has been extracted around $Q^2=0.4\mathrm{}$ ${\mathrm{GeV}}^2{/c}^2.$ In both cases the form factor values agree well with the ones extracted from processes on the deuteron. Our results are based on Faddeev solutions, modern NN forces, and partially on the incorporation of mesonic exchange currents.

The double-folding formalism for the $\alpha$-nucleus optical potential is revised to study the exchange effects and density dependence of the effective nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ interaction in detail. A realistic density dependent M3Y interaction, based on the G-matrix elements of the Paris NN potential, has been used in the folding calculation. The local approximation for the nonlocal one-body density matrix in the calculation of the exchange potential was tested by using the harmonic oscillator representation of the nonlocal density matrices of the $\alpha$-particle and target nucleus. The inclusion of a realistic density dependence into the effective NN interaction was shown to be vital for a correct description of the refractive $\alpha$-nucleus scattering data. A high sensitivity of the density distributions of the $\alpha$-particle and target nucleus to the shape of the $\alpha$-nucleus potential was found, which can be used in the folding analysis to test various density models for the $\alpha$-particle and target as well as to choose the most realistic approximation for the overlap density in the dinuclear system. Our results also stress the importance of $\alpha$-nucleus scattering experiment in the nuclear structure study.

Gamow-Teller single $\beta$ decay transitions $(\Delta J=1,$ $\Delta \pi =0,$ $\Delta T_z=\pm 1),$ at finite temperatures and between states of even-even and odd-odd mass nuclei, are calculated in the framework of the extended quasiparticle random phase approximation. Finite temperature blocking effects and particle-particle interactions are discussed in connection with the fragmentation of strength. It is shown that the inclusion of scattering terms, both in the phonons and in the transition operator, is needed to achieve the complete conservation of the transition strength. The calculations were performed in the mass region $A=106\mathrm{}$ and for temperatures lower than the critical value $T_c$ associated to the collapse of the pairing gaps ${(T}_c\cong 0.7\hspace{0.5em}\mathrm{MeV}).\mathrm{}$

The cross sections for the $\nu -d$ and $\overline{\nu }-d$ reactions are calculated for incident energy up to $E_{\nu }=170\mathrm{}\hspace{0.5em}\mathrm{MeV}$ with the use of a phenomenological Lagrangian approach. We assess and improve the reliability of the employed calculational method by examining the dependence of the results on various input and approximations that go into the calculation. The main points of improvement over the existing work are (1) use of the “modern” $\mathrm{NN}$ potentials, (2) use of the more accurate nucleon weak-interaction form factors, and (3) monitoring the strength of a vertex that governs the exchange-current contribution, with the use of data on the related process, $n+\overrightarrow{p}d+\gamma .$ In addition to the total cross sections, we present various differential cross sections that are expected to be useful for the SNO and other experiments. In the low-energy regime relevant to the solar neutrinos, the newly calculated total cross sections essentially agree with the existing literature values. The origins of slight differences found for higher energies are discussed. The ratio between the neutral-current and charged-current reaction cross sections is found to be extremely stable against any variations in the input of our calculation.

Differential cross sections, analyzing powers, and spin rotation parameters for elastic scattering of protons on ${}^4\mathrm{He}$ at 297 MeV have been measured over a wide angular range $(12\mathrm{}°<~{\theta }_{\mathrm{lab}}<~66°).\mathrm{}$ Experimental data have been microscopically analyzed with relativistic impulse approximation calculations. The spin observables up to medium scattering angles $({\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~40°)$ are predominantly sensitive to the ratio of the volume integral of scalar density to vector density. With a ratio of 0.92, which is significantly smaller than those for heavier nuclei (0.96–0.98), both spin observables as well as the differential cross section have been quantitatively reproduced. According to nuclear matter calculations, the small ratio reflects a high mass density. At backward angles, the experimental cross sections are larger than any of the values calculated with realistic density distributions.

The charge density distribution with respect to the velocity of matter produced in peripheral heavy ion reactions around Fermi energy is investigated. The experimental finding of enhancement of midrapidity matter shows the necessity to include correlations beyond Boltzmann-Uehling-Uhlenbeck (BUU) which was performed in the framework of nonlocal kinetic theory. Different theoretical improvements are discussed. While the in-medium cross section changes the number of collisions, it leaves the transferred energy almost unchanged. In contrast the nonlocal scenario changes the energy transferred during collisions and leads to an enhancement of midrapidity matter. The renormalization of quasiparticle energies can be included in nonlocal scenarios and leads to a further enhancement of midrapidity matter distribution. This renormalization is accompanied by a dynamical softening of the equation of state seen in longer oscillation periods of the excited compressional collective mode. We propose to include quasiparticle renormalization by using the Pauli-rejected collisions which circumvent the problem of backflows in Landau theory. Using the maximum relative velocity of projectile and targetlike fragments we associate experimental events with impact parameters of the simulations. For peripheral collisions we find reasonable agreement between experiment and theory. For more central collisions, the velocity damping is higher in one-body simulations than observed experimentally, because of missing cluster formations in the kinetic theory used.

We have applied the barrier-wave/internal-wave decomposition technique to ${}^{16}\mathrm{O}{+}^{16}\mathrm{O}$ elastic scattering optical model angular distributions between 75 and 145 MeV, an energy region where strong refractive effects—in particular Airy maxima and minima—are clearly observed; this technique, introduced in a semiclassical framework more than 20 years ago by Brink and Takigawa, and which was successful in clarifying the light-ion elastic scattering mechanism, has practically never been used in the context of light heavy-ion scattering. The decomposition is accomplished by using a fully quantum-mechanical method, which bypasses the intricacies of the semiclassical approach. The Airy minima are found to be due to the interference of the barrier-wave and internal-wave subamplitudes; the presence of a substantial internal-wave contribution demonstrates in a very clear way the exceptional transparency displayed by the ${}^{16}\mathrm{O}{+}^{16}\mathrm{O}$ system. The results obtained contrast with those of the nearside/farside decomposition technique, where the Airy minima are fully carried by the farside contribution. By combining the two approaches it is possible to calculate in a straightforward way the two components underlying the structure of the farside component, which up to now have been obtained through delicate semiclassical calculations or the use of an approximate empirical method. The complicated evolution of the full elastic cross section can eventually be explained in terms of the interference of several subamplitudes with a much smoother, and thus much simpler to understand, behavior. A barrier-wave/internal-wave decomposition of the 132 MeV ${}^{16}\mathrm{O}{+}^{12}\mathrm{C}$ and 100 MeV ${}^{18}\mathrm{O}{+}^{12}\mathrm{C}$ elastic scattering amplitudes is also presented.

The effect of scalar and vector meson mixing on the dilepton radiation from hot and dense hadronic matter is estimated in different isospin channels. In particular, we study the effect of $\sigma -\omega$ and $\rho -a_0$ mixing and calculate the corresponding rates. Effects are found to be significant compared to standard $\pi -\pi$ and $K-\overline{K}$ annihilations. While the mixing in the isoscalar channel mostly gives a contribution in the invariant mass range between the two-pion threshold and the $\omega$ peak, the isovector channel mixing induces an additional peak just below that of the $\phi .$ Experimentally, the dilepton signals from $\rho$-$a_0$ mixing seem to be more tractable than those from $\sigma -\omega$ mixing.

The original model of $q\overline{q}-\mathrm{b}\mathrm{o}\mathrm{u}\mathrm{n}\mathrm{d}$ states, developed by Gross and Milana, which uses the relativistic spectator (Gross) equations to give a manifestly covariant description of confinement in Minkowski space that is consistent with chiral symmetry, is improved and extended. These improvements include (i) derivation of the normalization condition for the relativistic wave functions, (ii) proof that confinement automatically prohibits decays by implying the vanishing of the vertex function when both quarks are on shell, (iii) extension of the model to the strange quark sector and to sectors with unequal quark masses, (iv) removal of unphysical singularities associated with the confining interaction, and (v) inclusion of a realistic one-gluon-exchange interaction. We use phenomenological quark mass functions to build chiral symmetry into the theory and to explain the connection between the current quark and constituent quark masses. We obtain reasonable results for pions and kaons, establishing that the formalism, designed to work well in the heavy quark sectors, can also be extended to the light quark sector.

A set of mass-dependent single-particle energies for sd shell-model calculations are derived from realistic forces using a set of two-body correlation functions with ${}^{16}\mathrm{O}$ taken as a closed-shell core. It is found that a constant mass-dependent shift applied to all the single-particle energies for any given mass number A in the range $16<~A<~40$ brings the calculated single-particle energies, the d-shell spin-orbit splitting, and the sd-shell splitting in line with their experimental counterparts derived from ${}^{17}\mathrm{O}$ spectrum. Since a constant shift to the single-particle energies can affect only the relative binding energies of the different isobaric states but not their spectroscopy, we conclude that for calculations in the sd shell, where ${}^{16}\mathrm{O}$ is taken as a closed shell core, it is sufficient to use single-particle energies derived from ${}^{17}\mathrm{O}$ to calculate the spectroscopy of nuclei over the whole sd-shell mass range. This analysis supports the use of mass-independent single-particle energies in earlier calculations in the sd shell.

Recent published data on the isoscalar gap in symmetric nuclear matter using the Paris force and the corresponding BHF single particle dispersion are corrected, leading to an extremely high proton-neutron gap of $\Delta \sim 8$ MeV at $\rho \sim 0.5{\rho }_0.$ Arguments of whether this value can be reduced due to screening effects are discussed. A density dependent delta interaction with cutoff is adjusted so as to approximately reproduce the nuclear matter values with the Paris force.