Two-loop corrections for nuclear matter, including vacuum polarization, are calculated in the Walecka model to study the loop expansion as an approximation scheme for quantum hadrodynamics. Criteria for useful approximation schemes are discussed, and the concepts of strong and weak convergence are introduced. The two-loop corrections are evaluated first with one-loop parameters and mean fields and then by minimizing the total energy density with respect to the scalar field and refitting parameters to empirical nuclear matter saturation properties. The size and nature of the corrections indicate that the loop expansion is not convergent at two-loop order in either the strong or weak sense. Prospects for alternative approximation schemes are discussed.

Total cross sections for the p${+}^{13}$C and p${+}^{16}$O reactions were measured by the activation method up to 30 MeV. Yields of ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ and of other produced nuclei ${(}^{11}$C${,}^{15}$O) were obtained.

In relativistic descriptions of the mean field in nuclei or in nuclear matter, the expression ‘‘effective mass’’ has been used to denote different quantities. The relationship between these various quantities is clarified. It is exhibited which one among them is most closely related to the effective mass that is derived from nonrelativistic analyses of scattering and bound-state data. This nonrelativistic-type effective mass has a characteristic energy dependence near the Fermi energy whenever one goes beyond the relativistic Hartree or Hartree-Fock approximations. By making use of dispersion relations that connect the real and imaginary parts of the microscopic mean field, it is shown that the occurrence of this ‘‘Fermi surface anomaly’’ is quite general. It has the same origin as in the nonrelativistic case, namely the frequency dependence of the mean field. Despite this qualitative similarity between the relativistic and nonrelativistic cases, a striking difference exists between the size of the Fermi surface anomaly in the two cases. The physical origins of the effective mass are also shown to be very different in the relativistic and nonrelativistic descriptions.

Precision measurements of the ${}_{}{}^3{}_{}{}^{}$H${\mathrm{-}}^3$He atomic mass difference afford a means for assessing the reliability of measurements of the electron antineutrino mass from tritium β decay. We show that a long-standing discrepancy between measurements of the ${}_{}{}^3{}_{}{}^{}$H${\mathrm{-}}^3$He mass difference obtained with tritium-implanted silicon detectors and those obtained by other techniques is due to neglect of chemical binding effects in the former experiments. The correction reconciles the silicon-detector results with modern determinations made by mass spectrometry and by β spectrometry. With this and other new data, a revised average value for the ${}_{}{}^3{}_{}{}^{}$H${\mathrm{-}}^3$He mass difference of 18 591(2) eV is found. The scatter in the extant data suggests the presence of systematic errors in some of the modern measurements, and at present there seems to be no compelling basis for a model-independent lower limit on the mass of ${\nu }_e$. .AE

The β- and γ-decay rates, electron scattering form factors, and intermediate energy (p,p’) and (p,n) cross-section data are used to compare a set of wave functions that have been proposed for ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$. With pertinent reaction t matrices and allowance for reasonable and often small core polarization corrections the wave functions derived by standard (shell-model) calculations are found to be the most relevant.

The structures of even Pt isotopes are studied with the traditional interacting boson approximation plus one-fermion-pair model. The energy spectra can be reproduced reasonably well if mixing of two bands of different deformation at low spins in these isotopes is considered. An apparent change of structure transiting from ${}_{}{}^{188}{}_{}{}^{}\mathrm{Pt}$ to ${}_{}{}^{186}{}_{}{}^{}\mathrm{Pt}$ was reflected in the different interactions needed to reproduce the energy spectra for heavier Pt isotopes (188≤A≤192) and lighter Pt isotopes (182≤A≤186), respectively. The compression of level spacing occurring between ${10}^{+}$ and ${12}^{+}$ states in heavier Pt isotopes is also obtained. The B(E2) values for ${}_{}{}^{184}{}_{}{}^{}\mathrm{Pt}$ yrast band versus the spins of the depopulating states are calculated and compared with the observed data.

The detailed features of the calculated energy-level schemes and of the single-particle, orbit-occupancy properties of the low-lying levels of the N=50 isotones ${}_{}{}^{80}{}_{}{}^{}\mathrm{Zn}$, ${}_{}{}^{81}{}_{}{}^{}\mathrm{Ga}$, ${}_{}{}^{82}{}_{}{}^{}\mathrm{Ge}$, ${}_{}{}^{83}{}_{}{}^{}\mathrm{As}$, ${}_{}{}^{84}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{85}{}_{}{}^{}\mathrm{Br}$, ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$, and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ are presented and discussed. These results are obtained with a new effective Hamiltonian operator obtained empirically from an iterative fit to experimental energies taken from all experimentally studied (A=82–96) N=50 nuclei. The model space for the calculations consists of active 0$f_{5/2}$, 1$p_{3/2}$, 1$p_{1/2}$, and 0$g_{9/2}$ proton orbits relative to a nominal ${}_{}{}^{78}{}_{}{}^{}\mathrm{Ni}$ core. This space is truncated internally by restricting the number of particles excited from the negative-parity orbits into the $g_{9/2}$ orbit to be no greater than four. The typical structures predicted for these lighter N=50 isotones are found to be dominated by well-mixed combinations of fp-orbit configurations, with the $g_{9/2}$ orbit playing a minor role in all but a few special cases. The model energy-level spectra are compared with existing experimental information, as are calculated spectroscopic factors for single-proton stripping and pickup reactions.

Differential cross sections and analyzing powers for ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$(d→,t${)}^{14}$N were measured up to 25 MeV excitation energy with 88 and 89 MeV polarized deuteron beams and magnetic spectrographs. States of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ up to 18.53 MeV have been studied in two experiments with overall resolutions of 25–70 keV, and j transfers were determined from their characteristic analyzing powers. Mixtures of different j transfers could be determined for those $1^{+}$ states where mixing was significant. Exact finite-range distorted-wave Born approximations calculations were used to deduce l transfers and spectroscopic strengths. The observed summed spectroscopic strength is 88% of the shell-model sum rule. Firm lower limits and tentative upper limits for six ($p_{1/2}$$p_{1/2}$${)}_J$,T and ($p_{3/2}$$p_{1/2}$${)}_J$,T residual two-nucleon matrix elements are deduced. Comparison with the widely used Cohen-Kurath matrix elements shows good agreement for four terms, but significant quantitative disagreement for the ($p_{1/2}$$p_{1/2}$${)}_0^{+}$,1 and ($p_{1/2}$$p_{3/2}$${)}_1^{+}$,1 terms. We also see significantly more than the predicted $p_{1/2}$$p_{3/2}$ mixing for the 3.948 MeV $1^{+}$,0 state. No appreciable pickup of s-d shell admixtures was seen up to 25 MeV excitation.

We calculate the finite nucleus Dirac mean field spectrum in a Galerkin approach using finite basis splines. We review the method and present results for the relativistic σ-ω model for the closed-shell nuclei ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. We study the convergence of the method as a function of the size of the basis and the closure properties of the spectrum using an energy-weighted dipole sum rule. We apply the method to the Dirac random-phase-approximation response and present results for the isoscalar $1^{\mathrm{-}}$ and $3^{\mathrm{-}}$ longitudinal form factors of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. We also use a B-spline spectral representation of the positive-energy projector to evaluate partial energy-weighted sum rules and compare with nonrelativistic sum rule results.

We propose a model for a relativistic many-body system at finite temperature in the framework of thermo field dynamics, which is a real-time formalism of finite-temperature field theory. Our model contains the scalar (σ) and the vector (ω) mesons as well as the Dirac nucleon. The full propagator and self-energy for each particle are presented in terms of spectral representations. The Feynman rules for a perturbation expansion are shown. They are applied to the study of collective modes in hot and dense matter within the random-phase approximation. The dispersion relations of the longitudinal and transverse collective modes in the meson branch are calculated. We also estimate the effective meson mass which is defined as the energy needed to create one meson at rest in extreme matter. The effects of vacuum fluctuations are also examined. They contribute a fair amount to the collective modes through the effective nucleon mass.

Evidence is presented for the existence of odd-even staggering in $K^{\mathrm{-}}$ rotational bands (with K>0) of odd-odd nuclei in the rare-earth and actinide regions. Coriolis-coupling calculations have been carried out for rotational bands in ${}_{}{}^{168}{}_{}{}^{}\mathrm{Tm}$, ${}_{}{}^{176}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{182}{}_{}{}^{}\mathrm{Ta}$, and ${}_{}{}^{182}{}_{}{}^{}\mathrm{Re}$. With these calculations, we are able to reproduce the odd-even staggering observed in these nuclei. In particular, the unusually strong staggering observed in the K${=2\mathrm{}}^{+}$ and $4^{\mathrm{-}}$ bands of ${}_{}{}^{182}{}_{}{}^{}\mathrm{Re}$ can be understood. Unusual features in the wave functions of some bands reflect the importance of couplings due to terms other than Coriolis in the Hamiltonian.

The half-life of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$ was reinvestigated by measuring the time-dependent yields of several nuclear γ-ray lines over a period of 280 days. The ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$ γ-ray yields were normalized to those observed from internal standards. A value of 77.08±0.08 days was deduced by averaging the results obtained from different γ-ray lines and source calibrations.

From γγ and γγ(θ) coincidence studies the second excited state of ${}_{}{}^{214}{}_{}{}^{}\mathrm{Po}$ has been identified at 1015.0±0.3 keV, with a most probable $J^{\pi }$${=4\mathrm{}}^{+}$. Transitions from known levels at 1543.5 and 1847.4 keV to the new level have been observed. Mixing ratios of $2^{+}$→$2^{+}$ transitions and level spins deduced earlier are used to classify a number of levels below 2 MeV in terms of the vibrational model. A level in ${}_{}{}^{214}{}_{}{}^{}\mathrm{Po}$ at 1743.0 keV has unambiguously been assigned a $J^{\pi }$${=0\mathrm{}}^{+}$ on the basis of γγ(θ) measurements. This $0^{+}$ state does not appear to be a member of a phonon multiplet.

We present a microscopic analysis of the nuclear spin response to proton excitation by examining the specific case of the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(p→,p→ ’) reaction. Recent results indicate that the spin-flip probability decreases with an increase in the incident proton energy from $E_p$=319 to 800 MeV but otherwise maintains the essential features of an enhancement at high excitation and a quenching at low excitation. We show that this feature is consistent with nuclear structure effects and is not likely to depend on the particular choice of proton beam energy. We also suggest that the decrease in spin-flip cross section with increasing $E_p$ is directly linked to the energy dependence of the t-matrix coefficients and conclude by presenting predictions for cross sections at lower incident proton energy.

Hartree-Fock-Rothaan calculations with realistic effective interactions in the sd shell consistently yield an ellipsoidal ground-state deformation for ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. The predictions of the present mean-field calculations are supported by experiment and exact shell-model calculations. For a deformed ground state with ellipsoidal symmetry two shape transformations are observed in the finite-temperature Hartree-Fock approximation as the temperature is increased, firstly from ellipsoidal to axially symmetric and finally to a spherical shape.

The pre-equilibrium component to the neutron spectra from fusion and quasifusion of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ with ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ at 20, 25, and 30 MeV/nucleon is evaluated by means of the exciton model using for the projectile nucleons an initial energy distribution resulting from the coupling of their translational and internal momenta. The use of a set of parameters deduced from the analysis of light-ion-induced reactions allows one to reproduce satisfactorily the experimental data.

A new economical numerical method is presented for the correct zero-range evaluation of differential cross sections and angular correlation functions for α-transfer reactions into high-lying unbound (resonant) α-cluster states. The results for the $5_1^{\mathrm{-}}$ (15.6 MeV) and $6_1^{+}$ (16.3 MeV) states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ occupied in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^6$Li,d${)}^{16}$${\mathrm{O}}^{\mathrm{*}}$/B (α${)}^{12}$C support the suggested approach.

It is shown that the polarizability of the bound nucleon is, within the errors in the total cross section measurements, the same as that of a free nucleon.