The ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(e,e’n${)}^1$H quasielastic cross section was measured at ${\mathit{Q}}^2$ values of 0.109, 0.176, and 0.255 (GeV/c${)}^2$. The neutron detection efficiency was determined by the associated particle technique with the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,pn) reaction for each of the three neutron kinetic energies. These ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(e,e’n) measurements of the coincidence cross sections are the first at low ${\mathit{Q}}^2$. The cross sections are sensitive primarily to the neutron magnetic form factor ${\mathit{G}}_{\mathit{M}}^{\mathit{n}}$ at these kinematics. The extracted ${\mathit{G}}_{\mathit{M}}^{\mathit{n}}$ values have smaller uncertainties than previous data and are consistent with the dipole parametrization at the two higher momentum transfers; at the lowest momentum transfer, the value of ${\mathit{G}}_{\mathit{M}}^{\mathit{n}}$ is ∼10% higher than the dipole value.

We evaluate the total cross section for pion production in the reaction pd→pd${\mathrm{\pi }}^0$ under the assumption that it is entirely due to the quasifree elementary process pn→d${\mathrm{\pi }}^0$. Close to threshold only large-momentum components of the target deuteron wave function can contribute. This provides a qualitative explanation of recent measurements of a surprisingly small near-threshold cross section for the pd→pd${\mathrm{\pi }}^0$ reaction. The final-state interaction between the proton and the deuteron in the exit channel is found to be significant. When it is taken into account the energy dependence of the measured pd→pd${\mathrm{\pi }}^0$ reaction is reproduced. We conclude that the main properties of the pd→pd${\mathrm{\pi }}^0$ reaction near threshold can be explained by a simple quasifree reaction model.

We develop a nonperturbative reduction scheme for the four-point vertex T of a generic field theory with interactions among bosons, fermions, and antifermions. We exhibit integral equations which express, in a manifestly crossing-symmetric way, the full vertex in terms of its two-particle irreducible part, together with the dressed three-point vertices and two-point propagators. This scheme generalizes the usual summation of ladder or bubble diagrams, thus providing for the consistent summation of a larger subset of all diagrams.

Vertex corrections are taken into account in the Schwinger-Dyson equation for the nucleon propagator in a relativistic field theory of fermions and mesons. The usual Hartree-Fock approximation for the nucleon propagator is known to produce the appearance of complex (ghost) poles which violate basic theorems of quantum field theory. In a theory with vector mesons there are vertex corrections that produce a strongly damped vertex function in the ultraviolet. One set of such corrections is known as the Sudakov form factor in quantum electrodynamics. When the Sudakov form factor generated by massive neutral vector mesons is included in the Hartree-Fock approximation to the Schwinger-Dyson equation for the nucleon propagator, the ghost poles disappear and consistency with basic requirements of quantum field theory is recovered.

One-loop corrections to threshold neutral pion photoproduction from protons are calculated in the linear sigma model. The total Born plus one-loop result is similar to that found using chiral perturbation theory (CHPT), and expansion of the threshold amplitude in ${\mathit{M}}_{\mathrm{\pi }}$/M reproduces the CHPT result to order (${\mathit{M}}_{\mathrm{\pi }}$/M${)}^2$. It is also shown that expansion of the amplitude in the external kinematical variables reproduces the ‘‘old’’ low-energy theorem. An in-depth study is made, in this model, of the validity and accuracy of expanding the amplitude in the external kinematical variables.

The ${}_{}{}^{31,32}{}_{}{}^{}\mathrm{Na}$ and ${}_{}{}^{31}{}_{}{}^{}\mathrm{Mg}$ beta decays were studied at the CERN on-line mass separator ISOLDE by gamma, gamma-gamma, and neutron-gamma measurements. In the ${}_{}{}^{31}{}_{}{}^{}\mathrm{Na}$ decay, the assignment of previously reported γ transitions and the observation of a new level at 3760 keV lead to a revised decay scheme which is found in good agreement with a calculation including two-particle–two-hole configurations in the model space, as far as only low-lying levels of ${}_{}{}^{31}{}_{}{}^{}\mathrm{Mg}$ are concerned. In the ${}_{}{}^{31}{}_{}{}^{}\to _{}^{31}{}_{}{}^{}$Al decay, a new decay scheme involves ten β branches and three states are reported for the first time. While satisfactory agreement with theoretical calculations is observed for excitation energies in ${}_{}{}^{31}{}_{}{}^{}\mathrm{Al}$, a strong discrepancy is observed for the intensity of the ground-state β branch, the experimental one being highly quenched as compared to theoretical expectations. Finally, new spectroscopic results have been obtained in the ${}_{}{}^{32}{}_{}{}^{}\mathrm{Na}$ β decay. A previously noninterpreted 1436 keV γ ray is now assigned in the ${}_{}{}^{32}{}_{}{}^{}\mathrm{Mg}$ scheme. The 240 keV ray is shown to arise from ${}_{}{}^{31}{}_{}{}^{}\mathrm{Mg}$ produced in the one-neutron channel, and to be related to the decay of an intruder state at ${\mathit{E}}_{\mathit{x}}$=461 keV. The latter is partially fed from the 1390 keV level. Both nicely compare with theoretical predictions locating 1ħω states at 0.40 MeV (7/$2^{\mathrm{-}}$) and 1.57 MeV (11/$2^{\mathrm{-}}$). The first experimental evidence for a γ cascade in the descendant ${}_{}{}^{32}{}_{}{}^{}\mathrm{Al}$ is also obtained.

The method of nonmetric multidimensional scaling has been used to attribute spins to a large number of proton capture resonances in five fp-shell nuclei, ${}_{}{}^{47}{}_{}{}^{}\mathrm{V}$, ${}_{}{}^{51}{}_{}{}^{}\mathrm{Mn}$, ${}_{}{}^{53}{}_{}{}^{}\mathrm{Mn}$, ${}_{}{}^{55}{}_{}{}^{}\mathrm{Co}$, and ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$, using as input information only the gamma decay branching ratios. The calibration of the method relies on the measured spins of a number of the resonances. In more than half the cases, a unique spin is found. The results of the analysis allow a reappraisal of analog states in the five nuclei.

The reaction ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$(p,p’) has been studied with an energy resolution of 4–5 keV using 22 MeV protons. Angular distributions for states up to 4 MeV excitation energies are compared with distorted-wave and coupled-channels calculations including one-step and two-step excitations to study direct and sequential strength distributions. The results are compared with calculations in the nuclear field theory approach where quasiparticle-random-phase-approximation-like states and their mixing with two-phonon (quadrupole and octupole) states is taken into account. Reasonable agreement is obtained for both the positive and the negative parity states.

Elastic electron scattering cross sections have been measured for ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ at 180° for 0.72<q<2.67 ${\mathrm{fm}}^{\mathrm{-}1}$. The M1 form factor has been extracted and a Fourier-Bessel analysis performed to obtain the ground-state magnetization density. Calculations including effects of core polarization have been performed within the framework of the finite Fermi system theory. These show a weakening of the strong repulsion in the spin-isospin channel and are in overall agreement with the data.

Excited states in ${}_{}{}^{82}{}_{}{}^{}\mathrm{Y}$ have been investigated via the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{28}$Si,3pn${)}^{82}$Y and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$${(}^{29}$Si,p2n${)}^{82}$Y reactions using beams provided by the Florida State University Tandem-LINAC with energies of 95 to 135 MeV. Particle-γ coincidences with a full-sphere charged-particle detector and an excitation curve were used to assign γ rays to ${}_{}{}^{82}{}_{}{}^{}\mathrm{Y}$. The ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$${(}^{29}$Si,p2n${)}^{82}$Y reaction at 95 MeV was used to measure γ-γ coincidences with five Compton-suppressed Ge detectors. Lifetimes in the ns and ps ranges were measured using direct timing and the Doppler-shift attenuation method. A level scheme with 39 states was constructed up to tentative spins and parities of (${15}^{\mathrm{-}}$) and (${21}^{+}$). In the positive-parity yrast band a phase reversal was observed in the signature splitting at I=10ħ. The B(M1) strengths in this band alternate with signature between about 0.1 and 1.0 ${\mathrm{\mu }}_{\mathit{N}}^2$. The B(E2) strengths of about 90 Weisskopf units are in good agreement with those predicted by Hartree-Fock-Bogolyubov calculations. Particle-rotor calculations indicate a prolate or triaxial core shape for the positive-parity band.

High-spin states of the odd-odd nucleus ${}_{}{}^{74}{}_{}{}^{}\mathrm{Br}$ were investigated via the reactions ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ ${(}^{19}$F,2pn${)}^{74}$Br and ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$${(}^{12}$C,3n${)}^{74}$Br at beam energies of 62 and 50 MeV, respectively. On the basis of coincidence data new levels have been introduced and partly grouped into rotational bands. Some of these new states decay to known levels of negative-parity bands built on both the ground state and the long-lived $4^{\mathrm{}(+)\mathrm{}}$ isomer. Thus, an excitation energy of 13.8 keV has been deduced for the long-lived isomer in ${}_{}{}^{74}{}_{}{}^{}\mathrm{Br}$. The level sequences observed are interpreted in terms of Nilsson configurations in conjunction with collective excitations.

The search for an η bound state in the double charge exchange (DCX) reaction ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$(${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$${)}^{18}$Ne(DIAS) has been carried out at LAMPF using the ${\mathit{P}}^3$ channel and the LAS spectrometer. An excitation function for this reaction was measured for energies ranging from 350 to 440 MeV and for momentum transfers of 0, 105, and 210 MeV/c. The measured cross sections tend to agree with previous results for DCX on ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$. The measured excitation function shows some evidence for structure near the η production threshold.

High spin states in the nucleus ${}_{}{}^{90}{}_{}{}^{}\mathrm{Tc}$ have been identified for the first time via the fusion evaporation reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{36}$Ar,3pn${)}^{90}$Tc, at 149 MeV beam energy. The OSIRIS spectrometer with an additional high purity Ge detector at 162° and several particle detectors were used to measure γγ and particle-γγ coincidences, directional correlations of oriented states (DCO’s), and line shapes due to Doppler-shift attenuation (DSA). Furthermore, an angular distribution experiment was performed with the reaction ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${(}^{35}$Cl,2pn${)}^{90}$Tc, at 120 MeV beam energy. Some 90 transitions were placed into a level scheme comprising 45 levels reaching up to a possible spin I=26ħ at 11.2 MeV excitation energy. Definite spin assignments for more than half of the levels were made via angular distribution coefficients and DCO ratios. Shell model calculations were performed in a restricted configuration space consisting of only the ${\mathit{p}}_{1/2}$ and ${\mathit{g}}_{9/2}$ orbitals. The level scheme can be reproduced very well up to spin I=21ħ. The predicted structure of the states is discussed and compared to those of neighboring isotopes.

Excited states of the Z=61 isotopes ${}_{}{}^{144}{}_{}{}^{}\mathrm{Pm}_{83}^{}{}_{}{}^{}$ and ${}_{}{}^{154}{}_{}{}^{}\mathrm{Pm}_{84}^{}{}_{}{}^{}$ have been studied in the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{130}$Te reaction at a beam energy of 85 MeV. Gamma-ray and conversion electron spectroscopy were used to establish the high spin states of ${}_{}{}^{144}{}_{}{}^{}\mathrm{Pm}$ up to spin 20ħ and to extend the level spectrum of ${}_{}{}^{145}{}_{}{}^{}\mathrm{Pm}$ up to a tentative spin of 33/2ħ. Empirical shell model calculations in a configuration space truncated to the π1${\mathit{h}}_{11/2}$, π1${\mathit{g}}_{7/2}^{\mathrm{-}1}$, and π2${\mathit{d}}_{5/2}^{\mathrm{-}1}$ protons and the ν2${\mathit{f}}_{7/2}$ neutron outside the ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ core reproduce the observed energy levels in good agreement with the experimental results. (π${\mathit{h}}_{11/2}$${)}^2$ configurations are suggested in an N=83 isotone for Z<64.

In the laboratory, ${}_{}{}^{91}{}_{}{}^{}\mathrm{Nb}$ decays by electron capture with a 680-yr half-life. However, as a high energy cosmic ray, it would be stripped of its atomic electrons and would be able to undergo only ${\mathrm{\beta }}^{+}$ decay. We produced and chemically purified a sample of ${}_{}{}^{91}{}_{}{}^{}\mathrm{Nb}$ and observed its decay with an array of Ge and NaI detectors. By following the ${\mathrm{\beta }}^{+}$ annihilation radiation, we were able to determine the ${\mathrm{\beta }}^{+}$ branching ratios of both the 105-keV, 61-d isomer and the ground state of ${}_{}{}^{91}{}_{}{}^{}\mathrm{Nb}$. The ground-state branch is (7.7±0.8)×${10}^{\mathrm{-}3}$% leading to a ${\mathrm{\beta }}^{+}$ partial half-like of (8.8±1.9)×${10}^6$ yr. Such a value of the half-life makes ${}_{}{}^{91}{}_{}{}^{}\mathrm{Nb}$ a good candidate for determining the confinement time of this secondary component of the cosmic rays.

Within the unified model of Bohr and Mottelson we derive the following linear energy weighted sum rule for low-energy orbital $1^{+}$ excitations in even-even deformed nuclei ${\mathit{S}}_{\mathrm{LE}}^{\mathrm{lew}}$(${\mathit{M}}_1^{\mathrm{orb}}$) ≃(6/5)ε [B(E2;$0_1^{+}$→$2_1^{+}$K=0)/${\mathit{Ze}}^2$〈${\mathit{r}}^2$${\mathrm{〉}}^2$]${\mathrm{\mu }}_{\mathit{N}}^2$ with B(E2) the E2 strength for the transition from the ground state to the first excited state in the ground-state rotational band, 〈${\mathit{r}}^2$〉 the charge rms radius squared, and ε the binding energy per nucleon in the nuclear ground state. It is shown that this energy weighted sum rule is in good agreement with available experimental data. The sum rule is derived using a simple ansatz for the intrinsic ground-state wave function that predicts also high-energy $1^{+}$ strength at 2ħw carrying 50% of the total ${\mathit{m}}_1$ moment of the orbital M1 operator.

A Monte Carlo approach is presented for the treatment of the pairing force in nuclear systems. Our method is computationally efficient and is very simple to implement. Numerical results are given and compared to an exact calculation and to the predictions of Bardeen-Cooper-Schrieffer (BCS) theory.

The role of the ρ-meson coupling constant ${\mathit{g}}_{\mathrm{\rho }}$ in relativistic mean field theory is investigated. It is observed that a slight variation in the adopted value of ${\mathit{g}}_{\mathrm{\rho }}$ gives a better agreement with the experimental binding energy. None of the properties included in the fitting procedure for fixing the Lagrangian parameters are affected by this fine tuning of the parameter ${\mathit{g}}_{\mathrm{\rho }}$ except the asymmetry energy which is altered by less than 0.4%.

The energy-corrected transition rates for γ decay of the n-capture states in ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$ and ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$ are calculated from data available in the literature. If one assumes that the capture states have good K values, the data reveal a significantly lower average transition rate when the normal K-selection rules are broken than for K-allowed transitions. The effect is more profound in the data from thermal neutron capture than in the data from 2 keV neutron capture.

We derive the equation of state of the quantum hydrodynamics Lagrangian in a classical approach. The obtained equation of state is then used as input in a relativistic hydrodynamical numerical routine. Rapidity and transverse momentum distributions are calculated and compared with experimental data on heavy ion collisions obtained at the Brookhaven National Laboratory Alternating Gradient Synchrotron and the CERN Super Proton Synchrotron.