The difficulties arising in the calculation of the nuclear curvature energy are analyzed in detail, especially with reference to relativistic models. It is underlined that the implicit dependence on curvature of the quantal wave functions is directly accessible only in a semiclassical framework. It is shown that also in the relativistic models quantal and semiclassical calculations of the curvature energy are in good agreement. © 1996 The American Physical Society.

We calculated the M1 strength distribution in ${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}$ within the quasiparticle-phonon nuclear model using the phonon basis for ${}_{}{}^{162}{}_{}{}^{}\mathrm{Dy}$. We found a strong fragmentation of the magnetic dipole strength in ${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}$ which was in qualitative agreement with the experimental data. The calculated fragmentation of the M1 strength in ${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}$ is much stronger in comparison with that in ${}_{}{}^{162}{}_{}{}^{}\mathrm{Dy}$. © 1996 The American Physical Society.

We investigate the Λ-attachment probabilities A to the fission fragments formed in Λ-accompanied nuclear fission. Assuming that initially the hyperon has an occupation probability of single-Λ states with a Gaussian form we study the influence of the shape of the scission configuration on the attachment probability. Only a weak dependence of A on the width and on the position of the center of the initial occupation distribution is found. Unfortunately it masks the also very weak dependence of this quantity on the shape of the scission configuration. © 1996 The American Physical Society.

When the Vlasov equation is investigated numerically using the method of test particles, the particle-particle interactions that inevitably arise in the simulation (but are not present in the Vlasov equation itself) result in an accumulation of errors which eventually drive the collection of test particles toward a state of classical thermal equilibrium. We estimate the rate at which these errors accumulate. © 1996 The American Physical Society.

In a recent paper [Phys. Rev. C 49, 2142 (1994)], Haberzettl presented cluster N-body equations for arbitrarily large systems of nucleons and mesons. Application to the three-nucleon system is claimed to yield a new kind of three-nucleon force. We demonstrate that these three-nucleon equations contain double counting. © 1996 The American Physical Society.

We point out that the results of relativistic mean field calculations for neutron-deficient Pt, Hg, and Pb isotopes by S. K. Patra et al. [Phys. Rev. C 50, 1924 (1994)] and S. Yoshida et al. [Phys. Rev. C 50, 1398 (1994)] contradict the large body of experimental data on these nuclei. In particular, we question their predictions of deformed ground states in the Pb isotopes and prolate and superdeformed ground states in the Hg isotopes. © 1996 The American Physical Society.

In reply to the Comment by Heyde et al., we discuss the sensitivity of the results of relativistic mean field (RMF) calculations on the shape of nuclei to the choice of input parameters in the Lagrangian of the σ,ω,ρ model and to the pairing gap in the BCS theory. © 1996 The American Physical Society.

The strength of final-state interaction (FSI) between struck proton and spectator neutron in ${}_{}{}^2{}_{}{}^{}\to$(e,${\mathit{e}}^{\prime }$p) scattering depends on the alignment of the deuteron. In the framework of the Glauber theory of FSI, which is relevant at GeV energies of the struck proton, we study the resulting FSI effects in the tensor analyzing power in detail and find substantial FSI effects starting at still low missing momentum ${\mathit{p}}_{\mathit{m}}$≳0.9 ${\mathrm{fm}}^{\mathrm{-}1}$. At larger ${\mathit{p}}_{\mathit{m}}$≳1.5 ${\mathrm{fm}}^{\mathrm{-}1}$, FSI completely dominates both missing momentum distribution and tensor analyzing power. We find that to a large extent FSI masks the sensitivity of the tensor analyzing power to models of the deuteron wave function. For the transversely polarized deuterons the FSI induced forward-backward asymmetry of the missing momentum distribution is shown to have a node at precisely the same value of ${\mathit{p}}_{\mathit{m}}$ as the plane-wave impulse approximation missing momentum distribution. The position of this node is not affected by FSI and can be a tool to distinguish experimentally between different models for the deuteron wave function. © 1996 The American Physical Society.

The leading-order isospin-violating force from simultaneous π and γ exchange is calculated. The charge-symmetric, but charge-dependent, force is calculated for static nucleons and in Coulomb gauge. Infrared divergences and other technical problems are discussed. The resulting force is roughly 3 orders of magnitude smaller than OPEP and roughly the same size as the Breit correction to single-photon exchange. The present calculation corresponds to a subset of one-loop diagrams in chiral perturbation theory for isospin violation in the nucleon-nucleon force. © 1996 The American Physical Society.

The photoproduction of vector mesons (ρ,ω,φ) is of renewed interest because intense high energy beams of polarized electrons and photons are under development. These beams and also polarized targets make it possible to explore the dynamics of basic baryon structure. As a step toward that goal, an analysis of all possible polarization observables for the case of vector meson photoproduction from a nucleon target is presented. The question of which observables are needed to determine completely the basic photoproduction amplitudes and the relationships between spin observables are addressed. Such theorems are most readily demonstrated by representing all observables as bilinear products of helicity amplitudes and using known properties of Dirac gamma and spin-1 matrices. The general angular dependence of spin observables, especially near thresholds and resonances, is examined for the vector meson case. The criteria for a complete set of observables and the relationships between observables are then presented. © 1996 The American Physical Society.

We have made high-resolution laser spectroscopy of the hyperfine structure of a radioactive isotope ${}_{}{}^{179}{}_{}{}^{}\mathrm{Ta}$ ($T_{\frac{1}{2}}=1.8\mathrm{}$ y) using an argon-ion sputtering atomic-beam source. From hyperfine constants $A$ and $B$ of the atomic ground state (${}_{}{}^4{}_{}{}^{}F_{\frac{3}{2}}^{}{}_{}{}^{}5d^{3}6s^2$), the magnetic dipole and electric quadrupole moments of the nuclear ground state of ${}_{}{}^{179}{}_{}{}^{}\mathrm{Ta}(I=\frac{7}{2})$ have been determined for the first time: ${\mu }_I^{179}=2.289\mathrm{}\left(9\right)\mathrm{}{\mu }_N$ and $Q_s^{179}=3.37\mathrm{}\left(4\right)\mathrm{}$ b. It is pointed out that magnetic moments of the ground and isomeric states in the region $N=102-112\mathrm{}$ can be systematically described in terms of the presently available theory while the revealed systematic behavior of electric quadrupole moments is hardly reproduced by the theory.

From a study of the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$(n,γ) reaction with thermal neutrons incident on a Teflon target, 168 γ rays have been detected and incorporated into a level scheme of ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ consisting of 35 previously known levels and a new one at 5939 keV. Two low-energy primary E1 transitions of energies 584 and 665 keV together account for more than half of the total capture cross section. They populate, respectively, states at 6018 and 5936 keV (both ${\mathit{J}}^{\mathrm{\pi }}$=$2^{\mathrm{-}}$). These states are also excited strongly in the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$(d,p) reaction. From each of these states, 17 γ rays were observed to the lower-lying states. These γ rays constitute the largest number of branches reported from any nuclear bound state. A weak (6±1μb)γ ray of energy 4630.6±0.9 keV, placed as a transition between the neutron-capturing state (which is a $0^{+}$ and $1^{+}$ mixture) and the 1971-keV, ($3^{\mathrm{-}}$) state, might represent the first observation of a primary M2 transition in the (n,γ) reaction. The total thermal-neutron-capture cross section of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ was measured as 9.51±0.09 mb; and the neutron separation energy of ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ as 6601.35±0.04 keV. Estimates of direct neutron capture have been made using physically realistic optical-model parameters. These model estimates are in reasonable agreement with the measured (partial) cross sections. While constructing the (n,γ) level scheme, the existing data on bound levels in ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ were critically evaluated.

The lifetime values for many levels are poorly known. Therefore, the lifetimes for 25 levels were measured by the Doppler-shift-attenuation method using the inverse reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}$${(}^{19}$F, pγ) on implanted deuterium targets. The experimental level properties such as excitation energies, ${\mathit{J}}^{\mathrm{\pi }}$ assignments, branching ratios, and lifetimes have been compared with the results from a large-basis shell-model calculation. The agreement was found to be quite good, but this comparison points out also the need for acquiring new data to give more definitive ${\mathit{J}}^{\mathrm{\pi }}$ assignments. © 1996 The American Physical Society.

An attempt was made to find the very neutron-rich isotope ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$ among the fragmentation products of a 90 MeV/nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ beam. This isotope has been predicted to be bound but was not observed in a previous experiment by Guillemaud-Mueller et al. As part of the search, the momentum distributions of all the oxygen isotopes in the range from ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ to ${}_{}{}^{24}{}_{}{}^{}\mathrm{O}$ were carefully determined so that the optimum separator setting for ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$ could be used. From an extrapolation of the counting rates of the lighter oxygen isotopes, we expected to observe several hundred events of ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$ during the measurement. However, no events could be attributed to ${}_{}{}^{26}{}_{}{}^{}\mathrm{O}$, thus indicating the particle instability of this isotope. The results for the production cross sections of 72 neutron-rich isotopes, ranging from ${}_{}{}^{38}{}_{}{}^{}\mathrm{P}$ to ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$, are presented and compared to predictions. © 1996 The American Physical Society.

The decay of high-spin states in the continuum of ${}_{}{}^{130}{}_{}{}^{}\mathrm{Ce}$ is studied via γ-ray and internal conversion electron spectroscopy. An electron surplus above predicted yields based on γ data is seen in coincidence with transitions in the yrast band of ${}_{}{}^{130}{}_{}{}^{}\mathrm{Ce}$. We attribute this to an admixture of electric monopole (E0) transitions with unstretched E2 and M1 transitions between strongly interacting bands of different deformations in the continuum. The E0 matrix elements needed to explain this surplus are comparable in magnitude to reported E0 matrix elements between discrete states in neighboring nuclei. © 1996 The American Physical Society.

The α decay characteristics of 88 decay lines emanating from 74 isotopes are presented, including new α decay lines identified in the neutron deficient nuclides ${}_{}{}^{158}{}_{}{}^{}\mathrm{Ta}$ (${\mathit{E}}_{\mathrm{\alpha }}$=5969±8 keV, ${\mathit{t}}_{1/2}$=46±4 ms), ${}_{}{}^{159}{}_{}{}^{}\mathrm{Ta}$ (${\mathit{E}}_{\mathrm{\alpha }}$=5516±5 keV, ${\mathit{t}}_{1/2}$=1100±100 ms), ${}_{}{}^{160}{}_{}{}^{}\mathrm{Ta}$ (${\mathit{E}}_{\mathrm{\alpha }}$=5313±5 keV, ${\mathit{t}}_{1/2}$=1700±200 ms), ${}_{}{}^{168}{}_{}{}^{}\mathrm{Ir}$ (${\mathit{E}}_{\mathrm{\alpha }}$=6323±8 keV, ${\mathit{t}}_{1/2}$=161±21 ms, ${\mathit{b}}_{\mathrm{\alpha }}$=82±14%), and ${}_{}{}^{170}{}_{}{}^{}\mathrm{Ir}$ (${\mathit{E}}_{\mathrm{\alpha }}$=6083±11 keV, ${\mathit{t}}_{1/2}$=830±300 ms, ${\mathit{b}}_{\mathrm{\alpha }}$=36±10%). Their correlations with other decay lines are discussed. The alpha decay of a high-spin isomer in ${}_{}{}^{157}{}_{}{}^{}\mathrm{Ta}$ has been discovered, with an energy of 7744±8 keV and a half-life of 1.7±0.1 ms, while the half-life of the corresponding isomeric alpha decay line of ${}_{}{}^{158}{}_{}{}^{}\mathrm{W}$ has been measured for the first time as 160±50 μs. First half-life and branching ratio measurements are also reported for the 5454±4 keV ${}_{}{}^{156}{}_{}{}^{}\mathrm{Lu}$ line (${\mathit{t}}_{1/2}$=494±12 ms), ${}_{}{}^{162}{}_{}{}^{}\mathrm{Re}$ (${\mathit{b}}_{\mathrm{\alpha }}$=85±9%), ${}_{}{}^{163}{}_{}{}^{}\mathrm{Os}$ (${\mathit{t}}_{1/2}$=${12}_{\mathrm{-}7}^{+11\mathrm{}}$ ms), ${}_{}{}^{166}{}_{}{}^{}\mathrm{Ir}$ (${\mathit{t}}_{1/2}$=12±1 ms), ${}_{}{}^{167}{}_{}{}^{}\mathrm{Ir}$ (${\mathit{t}}_{1/2}$=34±4 ms), the 6227±15 keV ${}_{}{}^{168}{}_{}{}^{}\mathrm{Ir}$ line (${\mathit{t}}_{1/2}$=125±40 ms), and ${}_{}{}^{171}{}_{}{}^{}\mathrm{Ir}$ (${\mathit{b}}_{\mathrm{\alpha }}$=58±11%). New decay measurements for the proton emitter ${}_{}{}^{156}{}_{}{}^{}\mathrm{Ta}$ (${\mathit{E}}_{\mathit{p}}$=1108±8 keV, ${\mathit{t}}_{1/2}$=375±54 ms, ${\mathit{b}}_{\mathit{p}}$=4.2±0.9%; ${\mathit{E}}_{\mathit{p}}$=1007±5 keV, ${\mathit{t}}_{1/2}$=144±24 ms) are presented. All energies have been measured using a consistent energy calibration procedure for protons and α particles. © 1996 The American Physical Society.

Lifetimes of ${}_{}{}^{160}{}_{}{}^{}\mathrm{Yb}$ yrast states at high rotational frequencies have been measured by the Doppler broadened line shape technique. Excited states in ${}_{}{}^{160}{}_{}{}^{}\mathrm{Yb}$ were populated by the reaction ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${(}^{44}$Ca,4n${)}^{160}$Yb at a beam energy of 200 MeV and the experimental measurements were carried out in the coincidence mode with an array of Compton-suppressed germanium detectors. The results for the ${24}^{+}$ to ${32}^{+}$ yrast states led to values of the transition quadrupole moments similar to those obtained for the lower members (ħω≤0.29 MeV) of the ground band in previous recoil-distance measurements. The trend of reducing ${\mathit{Q}}_{\mathit{t}}$ values found for the I=${34}^{+}$ and ${36}^{+}$ states are suggestive of band termination. The results are discussed in the light of current theoretical predictions. © 1996 The American Physical Society.

Six superdeformed (SD) bands have been observed in the nucleus ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$ using the γ-spectrometer GASP. The structure of the observed SD bands is discussed within the concept of cranked-Strutinsky-type calculations including pairing interaction. For the configuration assignments two different parametrizations of the Woods-Saxon potential are compared. Five of the observed SD bands are described in terms of quasiparticle configurations, whereas one is suggested to have vibrational-like structure. From this data a ΔI=2 staggering in the rotational spectrum of the yrast SD band also has been observed. © 1996 The American Physical Society.

Inelastic scattering of 180 MeV ${\mathrm{\pi }}^{+}$ and ${\mathrm{\pi }}^{\mathrm{-}}$ from ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$ shows an angular distribution for the $2_2^{+}$ state at 2.96 MeV that differs greatly from the usual L = 2 shapes for $2^{+}$ states. This state is perhaps the only case from pion-inelastic scattering in which standard distorted-wave impulse approximation models (including multistep and single-step responses) fail to reproduce the measured angular distribution. Furthermore, this unique excitation has been shown to have the features expected of a seniority-four proton excitation yet the pion data show charge symmetry. While coupled-channel calculations are not able to reproduce the pion data, they do agree with the shape observed for 42 MeV α particle scattering to this state, but the magnitude of the α scattering data is not consistent with a collective model and known γ ray deexcitations. Scattering to the first and third $2^{+}$ states of ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$ with pions and α particles is also considered, and found to match the usual result for $2^{+}$ states in general, accentuating the anomaly of this $2_2^{+}$ transition. © 1996 The American Physical Society.

We have investigated the role of proton-neutron pairing in the context of the quasiparticle random phase approximation formalism. This way the neutrinoless double beta decay matrix elements of the experimentally interesting A = 48, 76, 82, 96, 100, 116, 128, 130, and 136 systems have been calculated. We have found that the inclusion of proton-neutron pairing influences the neutrinoless double beta decay rates significantly, in all cases allowing for larger values of the expectation value of light neutrino masses. Using the best presently available experimental limits on the half lifetime of neutrinoless double beta decay we have extracted the limits on lepton number violating parameters. © 1996 The American Physical Society.

The phenomenon of s-wave intruder orbits is examined for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$ isotopes. Although ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ has an s-wave ground state, a three-body model of two neutrons + ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ can only reproduce the properties of ${}_{}{}^{12}{}_{}{}^{}\mathrm{Be}$ if the valence neutrons occupy mainly the (${\mathit{p}}_{1/2}$${)}^2$ configuration with about 25% admixture of (sd${)}^2$ configurations. For ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$, the possibility of low-lying s-wave states in ${}_{}{}^{13}{}_{}{}^{}\mathrm{Be}$ means that a wide range of models are compatible with the existing radius and momentum measurements, though some s admixture is necessary for binding. We show which kinds of momentum and Coulomb breakup measurements will be necessary to elucidate the structure of the ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$ halo. © 1996 The American Physical Society.