We analyze the structure of the amplitudes for electroweak bremsstrahlung in nucleon-nucleon collisions, for the charged $(N+\overrightarrow{N}{N+N+e}^{-}+{\overline{\nu }}_e)$ and neutral $(N+\overrightarrow{N}N+N+{\nu }_f+{\overline{\nu }}_f)$ weak current. Theorems are derived for the matrix elements of the vector and axial-vector currents in the soft regime. A comparison is made with previous work, usually performed in the nonrelativistic limit and by using a one-pion exchange two-nucleon interaction in Born approximation. Such approaches are argued to be unrealistic. This is explicitly shown for the neutrino-pair emission process in neutron-neutron scattering. Our results are relevant for calculations of neutrino emissivities in supernovae and in cooling scenarios of neutron stars.

We study the fluctuation properties of $\Delta T=0\mathrm{}$ electromagnetic transition intensities and electromagnetic moments in $A\sim 60$ nuclei within the framework of the interacting shell model, using a realistic effective interaction for $\mathrm{pf}$-shell nuclei with a ${}^{56}\mathrm{Ni}$ core. The distributions of the transition intensities and of the electromagnetic moments are well described by the Gaussian orthogonal ensemble of random matrices. In particular, the transition intensity distributions follow a Porter-Thomas distribution. When diagonal matrix elements (i.e., moments) are included in the analysis of transition intensities, the distributions remain Porter-Thomas except for the isoscalar $M1.\mathrm{}$ This deviation is explained in terms of the structure of the isoscalar $M1\mathrm{}$ operator.

This paper presents a further application of a new model for the effective two-body nucleon-nucleon interaction using a density-dependent separable monopole (SMO) interaction. This model has recently been successfully used for calculating the ground-state properties of spherical, doubly closed-shell nuclei from ${}^{16}\mathrm{O}$ to ${}^{208}\mathrm{Pb}$ and is used here to calculate properties of infinite symmetric nuclear matter and the beta-stable $n+p+e+\mu$ matter of relevance for neutron stars. An equation of state (EOS) is constructed for this and is joined smoothly onto the Baym, Pethick, and Sutherland EOS for baryon number densities below $n=0.1\mathrm{}{\mathrm{fm}}^{-3}$ and onto the widely used Bethe-Johnson EOS at $n=0.5\mathrm{}{\mathrm{fm}}^{-3}.$ Nonrotating, zero-temperature neutron-star models have been calculated for this composite EOS and the results obtained are compared with those for models calculated with the Skyrme effective interaction and with realistic nucleon-nucleon potentials. The SMO interaction is shown to give excellent global agreement with a wide range of expected properties of infinite nuclear matter and of neutron stars.

The Faddeev technique is employed to study the influence of both particle-particle and particle-hole phonons on the one-hole spectral function of ${}^{16}\mathrm{O}.$ Collective excitations are accounted for at a random phase approximation level and subsequently summed to all orders by the Faddeev equations to obtain the nucleon self-energy. An iterative procedure is applied to investigate the effects of the self-consistent inclusion of the fragmentation in the determination of the phonons and the corresponding self-energy. The present results indicate that the characteristics of hole fragmentation are related to the low-lying states of ${}^{16}\mathrm{O}.$

Neutron number dependence of neutron skin thickness in several isotopes is discussed by using Skyrme Hartree-Fock (HF) calculations. It is shown that the size of neutron skin is proportional to one-third power of the neutron number in all the isotopes studied although the central density varies substantially in each isotope. The isospin structure of giant quadrupole resonances (GQR) is also studied using self-consistent HF + random phase approximations. The isovector GQR is found to be a good isospin mode even in very neutron-rich nuclei, while the isoscalar GQR shows a large deviation from the pure isospin mode in neutron-rich C and O isotopes due to a strong neutron skin effect.

At low energies the particle-hole ${(NN}^{-1})$ part of the pionic susceptibility in isospin-symmetric nuclear matter is known to behave very differently from the susceptibility in finite nuclei due to the presence of an energy gap in the ${\mathrm{NN}}^{-1}$ excitation spectrum. In this Brief Report we show that for charged pions in $N\ne Z$ nuclei the changes due to the gap are very similar to those in the symmetric case, except at very low momenta, where a qualitatively different behavior is found.

An effective interaction is derived for use in the full $\mathrm{pf}$ basis. Starting from a realistic G-matrix interaction, 195 two-body matrix elements and four single-particle energies are determined by fitting to 699 energy data in the mass range 47–66. The derived interaction successfully describes various structures of $\mathrm{pf}$-shell nuclei. As examples, systematics of the energies of the first $2^{+}$ states in the Ca, Ti, Cr, Fe, and Ni isotope chains and energy levels of ${}^{56,57,58}\mathrm{Ni}$ are presented. The appearance of a new magic number 34 is seen.

Highly-deformed rotational bands were established in ${}^{59}\mathrm{Ni}$ using the ${}^{40}\mathrm{Ca}{(}^{29}\mathrm{Si},2p2\mathrm{}\alpha {)}^{59}\mathrm{Ni}$ reaction. Lifetime measurements indicate that transition quadrupole moments of two of these bands decrease as they smoothly approach their maximum-spin states. The configurations of these bands as well as their band-terminating features are discussed based on configuration-dependent cranked Nilsson-Strutinsky calculations. These calculations indicate that, unlike similar bands observed previously in the region, the two bands in ${}^{59}\mathrm{Ni}$ maintain significant collectivity at their ${I=I}_{\max }$ states.

We analyze the results by chiral $\mathrm{NN}$ models for the two-nucleon system and calculate the predictions for the nucleon vector analyzing power of elastic nucleon-deuteron $\mathrm{}\left(\mathrm{Nd}\right)\mathrm{}$ scattering, $A_y,$ by these models. Our conclusion is that a quantitative chiral two-nucleon potential does not resolve the $\mathrm{Nd}$ $A_y$ puzzle (when only two-body forces are included).

In this paper, we investigate the short-range repulsion given by the quark cluster model employing an inverse scattering problem. We find that the local potential which reproduces the same phase shifts as those given by the quark cluster model has a strong repulsion at short distances in the $\mathrm{NN}{\hspace{0.5em}}^1{S}_0$ channel. There, however, appears an attractive pocket at very short distances due to a rather weak repulsive behavior at very high energy. This repulsion-attractive-pocket structure becomes more manifest in the channel which has an almost forbidden state, $\Sigma N(T=3/2\mathrm{})\mathrm{}{\hspace{0.5em}}^3{S}_1.$ In order to see what kinds of effects are important to reproduce the short-range repulsion in the quark cluster model, we investigate the contribution coming from the one-gluon-exchange potential and the normalization separately. It is clarified that the gluon exchange constructs the short-range repulsion in the $\mathrm{NN}{\hspace{0.5em}}^1{S}_0$ while the quark Pauli-blocking effect governs the feature of the repulsive behavior in the $\Sigma N(T=3/2\mathrm{})\mathrm{}{\hspace{0.5em}}^3{S}_1$ channel.

Levels in ${}^{196}\mathrm{Pt}$ have been studied via the ${}^{196}\mathrm{Pt}{(n,n}^{\prime }\gamma )$ reaction for a range of neutron energies from 1 to 8 MeV. A “white” spectrum of neutrons was produced at the LANSCE/WNR facility, and the incident neutron energy was determined by the time-of-flight technique. Analysis of measured $\gamma \gamma$ coincidence data and γ-ray excitation functions, obtained with the large-scale Compton-suppressed Ge spectrometer GEANIE, yielded 13 new levels and 24 new $\gamma$ rays below $E_x=3\mathrm{}\hspace{0.5em}\mathrm{MeV}$ in ${}^{196}\mathrm{Pt}.$ Interacting boson model (IBM) calculations with broken SO(6) dynamical symmetry were performed. A new experimental level was found to be a prime candidate for the $J^{\pi }{=4\mathrm{}}^{+},$ $\sigma =6,\hspace{0.5em}\tau =5\mathrm{}$ IBM state.

High-spin states in ${}^{184}\mathrm{Os}$ have been studied using the ${}^{170}\mathrm{Er}{(}^{18}\mathrm{O},4n)$ reaction at a beam energy of 85 MeV. Several new negative parity levels including a 48-ns $K^{\pi }{=(18\mathrm{}}^{-})$ isomer have been identified. Nilsson configurations for the levels are assigned by comparison with multiquasiparticle calculations. Potential-energy-surface calculations show an increasing influence of triaxiality in nuclear shapes at higher spins. The decay rate of the $K^{\pi }{=(18\mathrm{}}^{-})$ isomer is discussed in relation to the role of the K quantum number.

We measure 114 nuclide-production cross sections for an isotopically enriched ${}^{208}\mathrm{Pb}$ target bombarded with 1.0 GeV protons. The cross sections are determined using direct γ spectrometry with a high-resolution Ge detector. The cross sections are compared to another experiment which used γ spectrometry with a natural Pb target; our results average 7.5% less for nuclides measured in common. They are also compared to a kinematically inverse reaction of 1 GeV/nucleon ${}^{208}\mathrm{Pb}$ interacting with a hydrogen target; we find our results average 15% higher than those for (a different set of) common nuclides. We find there is a systematic discrepancy between the cross sections found from the two very different experimental techniques. We also compare our measurements to eight different models. We find most are fairly reliable in predicting cross sections for nuclides not too far away in mass from Pb, but differ greatly in their reliability for nuclides in the deep-spallation and fission mass regions. In the spallation region $\left(A\gtrsim 155\right),$ the CEM2K code, which includes an intranuclear cascade, followed by a preequilibrium stage, leading finally to equilibrium decay, gives the best representation of our data. In the center of the fission/fragmentation mass region, the INUCL code is the most accurate. INUCL includes the same basic ingredients of cascade, preequilibrium, and evaporation, but differs considerably in details. It also contains a comprehensive fission model, which is lacking in CEM2K. No simulation code tested is reliable for the entire mass range of nuclides measured.

We investigate elliptic flow in heavy ion collisions at intermediate energies. In doing this, we implement and use a lattice-Hamiltonian model of the nuclear interaction and we also study the effect of in-medium nucleon-nucleon cross sections that follow consistently from the momentum-dependence of the nuclear mean field.

In the first stage of each run of a neutron lifetime experiment, a magnetic trap is filled with neutrons. In the second stage of each run, neutron decay events plus background events are observed. In a separate experiment of multiple runs, only background signals are measured after refilling the trap. In one approach, the mean lifetime of the neutron is estimated by fitting a two-parameter exponential model to the background-corrected data. In a second approach, the neutron lifetime is estimated by fitting a more complicated model to the “neutron decay plus background” data and the “background-only” data coming from both experiments. In the second approach, we assume knowledge of a statistical model for the background. For each approach, we compute the asymptotic standard deviation of the lifetime estimate in terms of the time spent filling the trap, $T_f,$ the time spent observing decay events, $T_d,$ and the ratio, R, of the number of runs of “background only” experiments to primary “neutron decay plus background” experiments. For each approach, we minimize the asymptotic standard deviation of the lifetime estimate in terms of $T_f,$ $T_d,$ and R, for various cases. In one case, the background rate is assumed to be stationary. In another case, the background rate is nonstationary. The comparison of the two approaches is made on the basis of the minimized asymptotic standard deviations. For both cases, the second “joint” estimation strategy is superior to the “background-correction” estimation strategy for all cases studied.

The validity of the quantum-number-projected generator coordinate method (PGCM) is investigated within the proton-neutron single-j shell model. The results of the PGCM are compared with exact solutions in the shell model. It is concluded that the PGCM provides a good approximation of the shell model for low-lying collective states. In order to describe the proton-neutron relative motion such as a scissors mode, we also propose a truncation scheme in terms of the PGCM. Various classes of PGCM truncations are examined by changing sets of generator coordinates. Flexibility with respect to the choice of generator coordinates is advantageous to illuminate the underlying physics. As an application of the PGCM truncation, the $M1/E2\mathrm{}$ transition probabilities concerning the ${I=1\mathrm{}}^{+}$ scissors state are analyzed for nuclei exhibiting stable triaxiality. The electromagnetic properties are identified. Those are characteristic of the $O\left(6\right)\mathrm{}$ dynamical symmetry limit of the proton-neutron interacting boson model.

Isotope ratios of fragments produced at midrapidity in peripheral and central collisions of ${}^{114}\mathrm{Cd}$ ions with ${}^{98}\mathrm{Mo}$ target nuclei at $E/A=50\mathrm{}\hspace{0.5em}\mathrm{MeV}$ are compared. The influence of the size $\mathrm{}\left(A\right),$ density, $N/Z,$ $E^{*}/A,$ and $E_{\mathrm{flow}}/A$ of the emitting source on the measured isotope ratios was explored by comparison with a statistical model (SMM). The midrapidity region associated with peripheral collisions does not appear to be neutron-enriched relative to central collisions.

The dispersion relations for the nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ T matrix in the framework of the Bethe-Salpeter equation for a two spin-one-half particle system with a separable kernel of interaction are considered. The developed expressions allow us to find explicit analytic connection between parameters of the separable kernel and low-energy scattering parameters and deuteron binding energy and to construct the rank-I separable kernel of interaction for S partial waves in singlet and triplet channels. The obtained kernel is used to calculate phase shifts. We presume that the approach can be extended—with a reasonable effort—to higher partial waves for $\mathrm{NN}$ scattering and other reactions $(\overline{N}N,$ $\pi N$ scattering).

The process ${}^3\mathrm{He}\to {(e,e}^{\prime }\overrightarrow{p})d$ [or ${}^3\mathrm{He}\to {(e,e}^{\prime }\overrightarrow{d}\left)p\right]$ is studied theoretically in a Faddeev treatment with the aim to have access to the spin dependent momentum distribution of $\overrightarrow{p}\overrightarrow{d}$ clusters in polarized ${}^3\mathrm{He}.$ Final state interactions and meson exchange currents turn out to have a strong influence in the considered kinematical regime (below the pion threshold). This precludes direct access to the momentum distribution except for small deuteron momenta. Nevertheless, the results for the longitudinal and transverse response functions are interesting as they reflect our present day understanding of the reaction mechanism and therefore data would be very useful.