The observables measured in two-body reactions, such as cross sections, polarizations, spin correlations, and the singlet fraction, take on simpler forms at threshold since only a few partial waves contribute. A study of these observables at the p¯p→Λ¯Λ threshold is made in this paper. Our results are compared to the recent LEAR PS185 measurements, and several interesting angle-dependent features of the data are seen to originate from normal threshold behavior. Using general threshold properties, some recently proposed physics models of this process are strictly tested in this energy region. Several constraints on the transition amplitudes are deduced and excellent fits to the data are achieved using a simple scattering length approach. We find that S-wave amplitudes, S-P interference, a strong tensor interaction, and P-wave splitting all play appreciable roles in the reaction near threshold.

The reported breakdown of the low energy theorem (LET) for p(γ,${\mathrm{\pi }}^0$) as deduced from recent measurements at Mainz and earlier at Saclay is reexamined and found to be premature. Both qualitative and quantitative arguments are presented that suggest the conventional LET disagrees with experiment at the 8–12 % level. There is, however, a strong quenching of ${\mathit{E}}_0^{+}$(${\mathrm{\pi }}^0$) near the ${\mathrm{\pi }}^{+}$ threshold which is described by a semiphenomenological rescattering calculation based on the integral equation for the transition operator. The results are in good agreement with the values of ${\mathit{E}}_0^{+}$(${\mathrm{\pi }}^0$) deduced from the Mainz experiment, as well as the differential cross sections. Comparisons are made with other data up to ${\mathit{E}}_{\gamma }$=300 MeV.

The absorption channel in π${\mathrm{-}}^3$He collisions is investigated. Amplitudes are derived for the pion-induced breakup of the target into both two clusters and three free nucleons. We employ elementary absorption mechanisms of one- and two-body type, which are presently considered to be important for the description of π-nucleus collisions from the low-energy region up to the region dominated by the Δ resonance. We put the major emphasis on the few-body aspects of the process, such as the three-nucleon dynamics in the final state, and the initial-state breakup of the bound nuclear system in presence of the pion. On the other hand, we neglect pion-nucleus correlations in the initial state, which would entail a complete four-body treatment of the process. For both one- and two-body elementary absorption, the full amplitudes are explicitly represented through quasiparticle (Sturmian) expansions. The entire set of graphs corresponding to the present model is given and discussed.

The Chandler-Gibson (CG) N-body equations are tested by considering the problem of three nonrelativistic particles moving on a line and interacting through attractive delta-function potentials. In particular, the input Born and overlap matrix-valued functions are evaluated analytically, and the CG equations are solved using a B-spline collocation method. The computed scattering matrix elements are within 0.5% of the known exact solutions, and the corresponding scattering probabilities are within 0.001% of the exact probabilities, both below and above the 3-body breakup threshold. These results establish that the CG method is practical, as well as theoretically correct, and may be a valuable approach for solving certain more complicated N-body scattering problems.

The full Bonn potential, combined with a relativistic quark-gluon annihilation potential, is compared with recent NN¯ polarization data from LEAR and with measured differential cross sections (elastic and charge exchange) below ${\mathit{p}}_{\mathrm{lab}}$=800 MeV/c. It is demonstrated within this approach that a careful analysis of pp¯→pp¯(EL) and pp¯→nn¯(CEX), at the same energy, in terms of the five independent helicity amplitudes can be used to selectively test specific boson exchange contributions to NN¯ scattering. The charge-exchange differential cross section in forward direction is particularly sensitive to the one-pion-exchange potential in this model. This feature could be used to see if recent attempts to fit NN data with a much softer πNN form factor can be made compatible with NN¯ data.

A bremsstrahlung amplitude in the special two-energy-two-angle (TETAS) approximation, which is relativistic, gauge invariant, and consistent with the soft-photon theorem, is derived for the pion-proton bremsstrahlung (${\mathrm{\pi }}^{+}$pγ) process near the ${\mathrm{\Delta }}^{++}$(1232) resonance. In order to take into account bremsstrahlung emission from an internal ${\mathrm{\Delta }}^{++}$ line with both charge and the anomalous magnetic moment ${\lambda }_{\mathrm{\Delta }}$, we have applied a radiation decomposition identity to modify Low’s standard prescription for constructing a soft-photon amplitude. This modified procedure is very general; it can be used to derive the TETAS amplitude for any bremsstrahlung process with resonance. The derived TETAS amplitude is applied to calculate all ${\mathrm{\pi }}^{+}$pγ cross sections which can be compared with the experimental data. Treating ${\lambda }_{\mathrm{\Delta }}$ as a free parameter in these calculations, we extract the ‘‘experimental’’ magnetic moment of the ${\mathrm{\Delta }}^{++}$, ${\mathrm{\mu }}_{\mathrm{\Delta }}$, from recent data. The extracted values of ${\mathrm{\mu }}_{\mathrm{\Delta }}$ are (3.7–4.2)e/(2${\mathit{m}}_{\mathit{p}}$) from the University of California, Los Angeles data and (4.6–4.9)e/(2${\mathit{m}}_{\mathit{p}}$) from the Paul Scherrer Institute data. Here, ${\mathit{m}}_{\mathit{p}}$ is the proton mass.

These values are smaller than the value 5.58e/(2${\mathit{m}}_{\mathit{p}}$), the ‘‘bare’’ magnetic moment predicted by the SU(6) model or the quark model, but they are close to the value 4.25e/(2${\mathit{m}}_{\mathit{p}}$) predicted by the modified SU(6) model of Beg and Pais and to the value (4.41–4.89)e/(2${\mathit{m}}_{\mathit{p}}$) predicted by the corrected bag-model of Brown, Rho, and Vento. Using the extracted ${\mathrm{\mu }}_{\mathrm{\Delta }}$ as an input for calculating ${\mathrm{\pi }}^{+}$pγ cross sections, we show that the overall agreement between the theoretical predictions calculated with the extracted ${\mathrm{\mu }}_{\mathrm{\Delta }}$ and the experimental measurements is excellent. This agreement demonstrates that the TETAS amplitude can be used to describe almost all the available ${\mathrm{\pi }}^{+}$pγ data. Finally, we also treat ${\lambda }_{\mathrm{\Delta }}$ as a complex quantity, ${\lambda }_{\mathrm{\Delta }}$=${\lambda }_{\mathit{R}}$+i${\lambda }_{\mathit{I}}$, in order to estimate the contribution from the imaginary part ${\lambda }_{\mathit{I}}$. The best fit to the data gives ${\lambda }_{\mathit{I}}$≊0, independent of the choice of ${\lambda }_{\mathit{R}}$. This fact implies that further dynamical corrections to the TETAS amplitude from the open pion-proton channel are small. Therefore, there is a good reason to believe that the ‘‘experimental’’ magnetic moment, which is very close to the ‘‘bare’’ magnetic moment predicted by the modified SU(6) or the quark model with corrections, should be nearly equal to the ‘‘effective’’ magnetic moment.

The K-internal conversion coefficients of the $2_2^{+}$→$2_1^{+}$ and $2_3^{+}$→$2_1^{+}$ transitions in ${}_{}{}^{110}{}_{}{}^{}\mathrm{Cd}$ and the $2_3^{+}$→$2_1^{+}$ transition in ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cd}$ have been measured. The available experimental information on K-conversion coefficients, mixing ratios E2/M1, and lifetimes for the $2_{\mathit{i}}^{+}$→$2_{\mathit{f}}^{+}$ transitions in ${}_{}{}^{110,112,114}{}_{}{}^{}\mathrm{Cd}$ have been utilized to deduce the ratios B(E0)/B(E2), and B(E0)/B(M1) and the monopole strength parameter ${\mathrm{\rho }}^2$. The experimental data are compared to the theoretical values calculated in the framework of the interacting proton-neutron boson model. By exploiting also the available data on ${\mathrm{\rho }}^2$ for the $0_2^{+}$→$0_1^{+}$ transitions in these nuclei the boson effective charges in the E0 operator have been deduced.

Excitation functions have been measured for the production of various isotopes of Bk, Cf, Es, and Fm from the interactions of 174- and 239-MeV ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ projectiles with ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$. The isotopic distributions were symmetric and displayed full widths at half maximum of 2.5, 2.5, and 2.25 mass units for Bk, Cf, and Fm, respectively. The maxima of the isotopic distributions occur for those reaction channels which involve the exchange of the fewest number of nucleons between the target and projectile for which the calculated excitation energy is a positive quantity. The maxima of the excitation functions occur at those projectile energies which are consistent with the calculated reaction barriers based upon a binary reaction mechanism. The effects of the odd proton in the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ projectile on the final isotopic distributions are discussed.

We have measured the invariant-mass spectrum of the final-state ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$+p system in the reaction T${(}^{16}$O${,}^{15}$N+p)X at 2.1A GeV with Be, Cu, and U targets (T). Electromagnetic dissociation of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ projectile nucleus in the Coulomb field of the target nucleus produces two prominent peaks in the proton-energy spectrum, one at 9 MeV, from transitions to the ground state of the residual ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ nucleus, and the other at 4 MeV, from transitions to excited states. This is corroborated by γ rays corresponding to the deexcitation of the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ nucleus which are in coincidence with the 4-MeV peak and are suppressed for the 9-MeV peak. Nucleon-nucleus diffractive dissociation makes a significant contribution to the cross section and results in a peak at 1.5 MeV. Nucleon-nucleon quasielastic scattering results in a featureless high-energy tail above 20 MeV.

The decay properties of ${}_{}{}^{155}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{155}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{155}{}_{}{}^{}\mathrm{Tm}$, and of the α-decay daughters ${}_{}{}^{151}{}_{}{}^{}\mathrm{Er}$ and ${}_{}{}^{151}{}_{}{}^{}\mathrm{Ho}$ were investigated following the on-line mass separation of A=155 nuclides produced in ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$ irradiations of ${}_{}{}^{95}{}_{}{}^{}\mathrm{Mo}$. In the study, the half-life of the low-spin isomer in ${}_{}{}^{155}{}_{}{}^{}\mathrm{Lu}$ was measured to be 140±20 ms, the β-decay branch of ${}_{}{}^{155}{}_{}{}^{}\mathrm{Yb}$ was identified by observing daughter γ rays and Tm K x rays, and the existence in ${}_{}{}^{155}{}_{}{}^{}\mathrm{Tm}$ of an ${\mathit{s}}_{1/2}$ isomer (${\mathit{T}}_{1/2}$=44±4 s), in addition to the ${\mathit{h}}_{11/2}$ ground state (${\mathit{T}}_{1/2}$=21.6±0.2 s) was established. Schemes for the β decays of ${}_{}{}^{155}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{155}{}_{}{}^{}\mathrm{Tm}$, and ${}_{}{}^{151}{}_{}{}^{}\mathrm{Er}$ are proposed. New information on ${}_{}{}^{151}{}_{}{}^{}\mathrm{Er}$ decay establishes the ${\mathit{s}}_{1/2}$ isomer in ${}_{}{}^{151}{}_{}{}^{}\mathrm{Ho}$ to be 41.1±0.2 keV above the ${\mathit{h}}_{11/2}$ ground state. Also, branchings of 90±5, 28±7, and ${80}_{\mathrm{-}20}^{+15\mathrm{}}$% were determined for the α decays of ${}_{}{}^{155}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{151}{}_{}{}^{}\mathrm{Ho}$, and ${}_{}{}^{151}{}_{}{}^{}\mathrm{Ho}_{}^{\mathit{m}}{}_{}{}^{}$, respectively.

Differential cross-section data from 0° to 8° for inelastic scattering of 129 MeV alpha particles exciting ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ in the region of 14–22 MeV have been analyzed to explore the existence of monopole strength at approximately ${\mathit{E}}_{\mathit{x}}$=17 MeV. The angular distribution for a peak at ${\mathit{E}}_{\mathit{x}}$=17.0 MeV with Γ=4.0 MeV is consistent with an E0 transition exhausting 19±10 % of the E0 energy-weighted sum rule (EWSR). The angular distributions for peaks at ${\mathit{E}}_{\mathit{x}}$=16.1 and 20.4 MeV with Γ=4.7 and 4.4 MeV, respectively, were fit by 52±10 % of the E2 EWSR and a combination of E2 (6.9±2.0 % EWSR) and E0 (2.$9_{\mathrm{-}2.9}^{+2.1\mathrm{}}$% EWSR).

The reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${+}^{12}$C at ${\mathit{E}}_{\mathrm{Ca}}$=160 MeV has been used to study high-spin states in the recoil-separated nuclides ${}_{}{}^{49}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{49}{}_{}{}^{}\mathrm{V}$, and ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ti}$. The latter two show distinctive ${\mathit{f}}_{7/2}$ shell-model behavior up to ${\mathit{J}}^{\mathrm{\pi }}$=27/$2^{\mathrm{-}}$ and ${12}^{+}$, respectively, while the first appears to be a collective rotor with a particle alignment at ${\mathit{J}}^{\mathrm{\pi }}$=17/$2^{\mathrm{-}}$. Rotorlike bands of sd-shell origin were seen in ${}_{}{}^{49}{}_{}{}^{}\mathrm{V}$ and ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ti}$ up to ${\mathit{J}}^{\mathrm{\pi }}$=11/$2^{+}$ and ${11}^{\mathrm{-}}$, respectively.

Systematic calculations of asymmetric nuclear matter have been performed in the framework of the Brueckner-Bethe-Goldstone approach in a wide range of both density and asymmetry parameter. The empirical parabolic law fulfilled by the binding energy per nucleon is confirmed by the present results in all the range of the asymmetry parameter values. The predominant role of the ${}_{}{}^3{}_{}{}^{}$${\mathit{S}}_{1\mathrm{-}}^3$${\mathit{D}}_1$ component of the NN interaction is elucidated. A linear variation of the proton and neutron single-particle potentials is found as increasing the neutron excess; a deviation from the phenomenological potentials occurs for highly asymmetric matter as an effect of the self-consistency. The present calculations of the incompressibility predict a strong softening of the equation of state going from symmetric to asymmetric nuclear matter. The proton fraction in equilibrium with neutron matter has been determined from the beta-stability condition and its relevance to the superfluidity of neutron stars has been investigated.

Gai et al. have proposed that cluster-molecular structure, in which a three- or four-particle cluster is well separated from the core, can be identified by the strong E1 transitions connecting cluster states with this structure. We use this signature to determine which cluster states in the A=14–19 region are cluster-molecular states. In addition, we note that such structure can also be recognized by comparing the results of three- and four-particle transfer reactions which populate the nucleus. In a nucleus possessing cluster-molecular structure, the three- and four-particle cluster strength lies in different states. We use this information to support the identification of molecular or nonmolecular structure in several nuclei. The examination of the transfer data also allows us to identify a nucleus, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, in which molecular and nonmolecular cluster states may coexist.

Arguments are put forward to suggest that a double hypernucleus event, recently reported by Aoki et al. as either ${}_{\Lambda \Lambda }{}^{10}{}_{}{}^{}\mathrm{Be}$ or ${}_{\Lambda \Lambda }{}^{13}{}_{}{}^{}\mathrm{B}$, should be interpreted as ${}_{\Lambda \Lambda }{}^{13}{}_{}{}^{}\mathrm{B}$. It is proposed that the formation of ${}_{\Lambda \Lambda }{}^{13}{}_{}{}^{}\mathrm{B}$ occurs sequentially via an intermediate excited state of ${}_{\Lambda \Lambda }{}^{14}{}_{}{}^{}\mathrm{C}$, which decays by proton emission: ${\Xi }^{-}+{}_{}{}^{14}{}_{}{}^{}\mathrm{N}\to n+{}_{\Lambda \Lambda }{}^{14}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}$, ${}_{\Lambda \Lambda }{}^{14}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}\to p+{}_{\Lambda \Lambda }{}^{13}{}_{}{}^{}\mathrm{B}$. Moreover, it is shown that particular excited states are favored in the ${\Xi }^{-}$ hyperon capture process. The binding energy of the two $\Lambda$ hyperons in ${}_{\Lambda \Lambda }{}^{13}{}_{}{}^{}\mathrm{B}$ is $B_{\Lambda \Lambda }=27.5\mathrm{}\pm 0.7$ MeV, corresponding to an attractive $s_{\Lambda }^2$ matrix element $\Delta B_{\Lambda \Lambda }=4.8\mathrm{}\pm 0.7$ MeV, in good agreement with values of $\Delta B_{\Lambda \Lambda }$ obtained from previous events.

A quantum-mechanical formalism to calculate the nuclear excitation by electron transition (NEET) is presented. Emphasis is on the explicit calculations of the transition matrix elements for electric multiple and magnetic dipole NEET and discussions of the selection rules. One of the features of this formalism is that the part of the matrix element in connection with the nuclear partner is related to the nuclear partial radiative width, which is a measurable quantity. This makes it available to evaluate the NEET probability more reliably. The predicted results for NEET probabilities in ${}_{}{}^{189}{}_{}{}^{}\mathrm{Os}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, and ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ are given along with the available measured data.

In the relativistic quantum mean field theory retardation effects are investigated for spherical nuclei throughout the Periodic Table. In a Hartree-Fock calculation retardation affects only the exchange terms; the exchange of σ, ω, ρ, and π mesons and photons are included. We find the retardation is important only for the pion; for the other heavier mesons its contribution is negligibly small. The total binding energy of a nucleus can be changed by about 5% when retardation is included. For the electric charge density appreciable difference is observed only for ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.

The negative-parity energy levels of the even-odd Yb isotopes, ${}_{}{}^{163}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{169}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{171}{}_{}{}^{}\mathrm{Yb}$, and ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$, are studied systematically within the framework of the extended interacting-boson-fermion-approximation (IBFA) model in which one odd fermion is couplied with a boson core. The boson core is described with the IBA model but allowing one boson to break into a quasifermion pair. The odd fermion is assumed to be in one of the ${\mathit{f}}_{7/2}$ and ${\mathit{p}}_{3/2}$ single-particle orbitals while the fermion pair is allowed to occupy the single-particle orbit ${\mathit{i}}_{13/2}$. It was found that the negative-parity energy levels of these even-odd Yb isotopes and the values of transition quadrupole moments for the ground-state rotational band of ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$ can be reproduced in fairly good agreement with the observed data.

A semiclassical model for α clustering in heavy nuclei is developed where the nucleus is viewed as a composite system of pairwise correlated nucleons interacting with α particles. The nucleons are treated microscopically by the use of a spherical shell-model basis while the α particles are considered as elementary bosons carrying angular momentum zero and one. The description of such a system is based on a time-dependent variational formalism, which yields BCS-like equations for the ground and some low-lying excited states. It is shown that the system may undergo transitions from a nucleon superfluid phase to intermediate phases characterized by the coexistence of few α clusters with a nucleon pair condensate. The model allows also to study in a random-phase-approximation context the fluctuations of the system around the BCS-like configurations. Two peculiar aspects emerge, the occurrence of collective states describing a wobbling motion of the α particles and the unusually large number of collective states describing a coherent motion of nucleons oscillating in phase with α particles. The numerical illustrative applications refer to ${}_{}{}^{220}{}_{}{}^{}\mathrm{Ra}$.

An exact expression for the mean free path in a relativistic description of nuclear matter is given. Corrections due to the spatial nonlocality are calculated. While the latter play a significant role in giving reasonable values for the mean free path in nonrelativistic models, they have minor effects in the relativistic description of the nuclear matter mean field.