We report a search for a short lived neutral particle φ emitted in the decay of the 15.1 MeV $J^{\pi }$(T${)=1\mathrm{}}^{+}$(1) state in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. The experiment is sensitive to φ→${\mathrm{e}}^{+}$${\mathrm{e}}^{\mathrm{-}}$ decays and finds no evidence for such a particle. We set upper limits on ${\Gamma }_{\phi }$/${\Gamma }_{\gamma }$ for mean lifetimes between ∼${10}^{\mathrm{-}13}$ and ∼${10}^{\mathrm{-}8}$ sec and in the mass range 1.02–2.5 MeV.

Levels of ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}$ populated following the ${\beta }^{\mathrm{-}}$ decay of the $0^{\mathrm{-}}$ ground state of ${}_{}{}^{96}{}_{}{}^{}\mathrm{Y}$ have been investigated by γ-ray and conversion electron singles, γ-ray multispectral scaling, γ-γ and γ-${\mathrm{e}}^{\mathrm{-}}$ coincidence, and γ-γ angular correlation measurements. These data have been used to establish the population of eight excited levels of ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}$, to confirm the $0^{+}$ assignment of the 2695-keV level, and to determine a half-life of 5.4(1) s for ${}_{}{}^{96}{}_{}{}^{}\mathrm{Y}$. The deduced beta transition strengths establish the decay to the ground state, with logft of 5.6, as one of the fastest first-forbidden decays known and support the notion of double subshell closure at Z=40 and N=56. The observed strong hindrance of transitions to excited $0^{+}$ states is indicative of shape coexistence. The observed level pattern of the band built on the $0_2^{+}$ state exhibits similarities to nearby vibrational-like nuclei having four valence protons and four valence neutrons. A four-particle, four-hole interpretation of the $0_2^{+}$ state is supported by the data, and we determine a deformation parameter, ${\beta }_2$∼0.2, for this intruder bandhead.

We make use of the auxiliary (bilocal) field technique in an attempt to understand the relation between modern relativistic models of nuclear structure and quantum chromodynamics. The advantage of the model introduced here is that we are able to discuss and interconnect chiral symmetry breaking, (nontopological) models of hadron structure, and relativistic quantum field theories of nuclear structure. The proposed relation of the auxiliary fields of this model to the fields which play a central role in Dirac phenomenology is an important aspect of our work. It can be seen that the large scalar fields used in Dirac phenomenology, which serve to reduce the mass of the nucleon (or the quarks), are a reflection of a partial restoration of chiral symmetry at finite baryon number, that is, within nuclear matter.

We use the eigenstate of the shape operators in second quantized form to give a geometrical interpretation to each boson excitation in the interacting boson model. For well-deformed systems a method is presented by which the intrinsic components of any boson number preserving operator can be calculated in second quantized form and to leading order in the boson number. In this way vibrational and rotational modes are identified and the corresponding excitation energies and moments of inertia are calculated to leading order in the boson number. The intrinsic components of the E2 transition operator are also calculated. Using these results several E2 transition rates are calculated to leading order in the boson number.

Differential cross sections for the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$(p,${\mathrm{p}}_0$), (p,${\mathrm{p}}_1$), (p,${\alpha }_0$), and (p,${\alpha }_1$) reactions were measured in the range $E_{\mathrm{p}=1.00\mathrm{}}$ to 4.01 MeV with an overall resolution of about 400 eV. The resonance parameters were extracted for 143 levels with a multilevel, multichannel R-matrix code. These parameters include resonance energy, total angular momentum, parity, partial widths, channel spin or orbital angular momentum mixing ratios, and, for some resonances, the relative signs of width amplitudes. Eight isobaric analog resonances were identified in ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$. Proton resonance strengths were compared with shell model predictions. The ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$(p,${\alpha }_0$) data were used to obtain the reaction rates for the inverse reaction ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$(α,${\mathrm{p}}_0$).

The lifetime of the yrast ${10}^{+}$ level at 3115 keV in ${}_{}{}^{132}{}_{}{}^{}\mathrm{Ba}$ has been measured as τ=10.8(9) ns. A pulsed ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ beam with a pulse width of 2.2 ns was thereby used in the reaction ${}_{}{}^{122}{}_{}{}^{}\mathrm{C}$,3n${)}^{132}$Ba. The backbending behavior of the yrast band and the B(E${2;10}^{+}$→$8^{+}$) values are compared with those in neighboring N=76 isotones.

The α-cluster structure of the ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ nucleus is investigated within a local potential model description, starting from the unique optical potential which describes elastic ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(α,α) scattering on broad angular and energy ranges, and which has recently been shown to describe the broad oscillations seen in the low energy fusion excitation function as well. It is found that the various α-cluster states group into quasirotational bands whose properties are not dissimilar to those of the well-understood ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ nucleus. The lowest lying band is composed of states of even parity with moderate cluster character at low spin; it agrees within a few MeV’s in absolute energy with the ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ experimental ground state band, and the experimental intraband quadrupole transition probabilities are reproduced with good accuracy. The potential supports an excited positive parity band with strong cluster character, starting a few MeV’s above the α${+\mathrm{}}^{40}$Ca threshold; the states of this band with spins ranging from 6 to 12 are responsible for the oscillations observed in the fusion excitation function. It supports, in addition, a negative parity band starting just above the threshold and composed of narrow states with intermediate cluster character; the latter has up to now no experimentally known counterpart. The states of higher lying bands are very broad and overlapping but they play an important role in enhancing the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(α,α) backward angle cross section. Our results are discussed in terms of the available experimental evidence and of the various, often conflicting theoretical interpretations which have been put forward to describe the ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ α-cluster spectroscopy.

The effect of temperature and angular momentum on the nuclear level density parameter is investigated. Pairing correlations and deformation degrees of freedom are also included. The level density parameter fluctuates at low temperatures and the effect of angular momentum is very pronounced at low temperatures. The variation of shell correction with angular momentum is also studied. Results for the nuclei ${}_{{\mathrm{}}^1{\mathrm{}}_{66}^{58}}{}^{}{}_{}{}^{}\mathrm{Dy}$, ${}_{{\mathrm{}}^1{\mathrm{}}_{78}^{94}}{}^{}{}_{}{}^{}\mathrm{Pt}$, and ${}_{{\mathrm{}}^1{\mathrm{}}_{70}^{70}}{}^{}{}_{}{}^{}\mathrm{Yb}$ are presented.

Fluctuations of selected observables and their dependence on the size of the system are studied within the framework of an exactly solvable model that mimics the interplay between pairing and long range forces. It is found that thermal mean-field results for fluctuations can yield an adequate estimate of the true fluctuations provided one evaluates those fluctuations in a particular manner.

A systematic procedure that allows for corrections of arbitrary order to the time-dependent Hartree-Fock approach is presented and illustrated with reference to an exactly solvable U(3) model. Substantial improvements over the uncorrelated picture are obtained.

The strength function for collective rotational transitions at high level density manifests itself in quasicontinuum gamma-ray spectra following heavy-ion fusion reactions. The tails of the strength distribution are considered here on the basis of results from a schematic model. In a weak interaction regime, the tails drop off rapidly. In a strong interaction regime, the tails of the standard Breit-Wigner shape are modulated by the level density and by the few-body nature of the residual interaction. This could reduce the B(E2) strength available for rotational decay.

An exactly soluble two-body model is used to investigate Coulomb effects on S-wave asymptotic normalization constants. The model consists of an S-wave separable interaction with and without a repulsive Coulomb interaction. Relative to the case without the Coulomb interaction, it is shown explicitly that an S-wave asymptotic normalization constant is affected in two compensating ways by the presence of the Coulomb interaction: (1) The asymptotic norm decreases due to the decrease in binding energy; (2) the asymptotic norm increases due to the modification in the tail of the wave function brought about by the long-range nature of the Coulomb interaction. For a system like ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, these are approximately 5% effects that essentially cancel each other, leading to nearly equal asymptotic normalization constants for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.

The electromagnetic properties of ground and excited states of nuclei with an odd number of particles and holes outside the closed shells are described in the j-j coupling shell model. The residual interaction between the valence particles and holes causes two different configuration mixing: (a) one where the valence particles and holes are scattered to higher shell model states, and (b) ones where the valence particles and holes excite particles out of the core. The electromagnetic properties of odd-even nuclei are sensitive to the correct treatment of both types of configuration mixing. In this paper the matrix elements of the nuclear Hamiltonian evaluated using the basis of configuration mixing states of types (a) and (b), and the resulting eigenvalue equations, have been exactly calculated. The matrix elements of the electromagnetic multipole operators calculated with the resulting eigenvectors of type (b) are then related to the deviation observed between the experimental and valence expectation values.

The role of the deuteron asymptotic D to S normalization ratio ${\eta }^{\mathrm{d}}$ in the calculation of triton observables is emphasized both within a simple model and in an exact numerical calculation. We suggest a new correlation among ${\eta }^{\mathrm{t}/{\eta }^{\mathrm{d}}}$ and $E_{\mathrm{t}}$ in dynamical three nucleon calculations, where ${\eta }^{\mathrm{t}}$ is the triton asymptotic D to S ratio and $E_{\mathrm{t}}$ is the triton binding energy. Studying this correlation we obtained ${\eta }^{\mathrm{t}/{\eta }^{\mathrm{d}=1.68\mathrm{}\pm 0.04}}$. .AE

It is shown that the ‘‘normal’’ and ‘‘decoupled’’ band-like structures recently observed in the nuclei ${}_{}{}^{133}{}_{}{}^{}\mathrm{Pr}$ and ${}_{}{}^{135}{}_{}{}^{}\mathrm{Pr}$ can be reproduced within the framework of a standard version of the particle-rotor model. In addition, several positive parity levels in ${}_{}{}^{135}{}_{}{}^{}\mathrm{Pr}$, to which no band assignment could be given earlier, are shown to be the members of two positive parity bands with opposite signatures based on the ${(3/2\mathrm{}}^{+}$[411] Nilsson orbital. The most interesting observation of the present work is the near total attenuation of the Coriolis interaction in the positive parity bands in ${}_{}{}^{135}{}_{}{}^{}\mathrm{Pr}$. It is suggested that this nucleus can be a very good testing ground for different versions of the particle-rotor models currently used by different workers.

We develop the theory of transport in nuclear superfluids well below the transition temperature. We adopt a Boltzmann-Fermi description of quasiparticle kinetics and a realistic one-pion-exchange Gaussian force with spin-isospin exchange. The microscopic transition rates generalize those occurring in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ problem. A partial wave treatment of the gap matrices makes evident anisotropy in the ${}_{}{}^3{}_{}{}^{}\mathrm{P}_2^{}{}_{}{}^{}$ state. Relaxation times and mean free paths on the Fermi surface of superfluid nuclear matter are computed for isotropic BCS, Balian-Werthamer, and anisotropic ${}_{}{}^3{}_{}{}^{}\mathrm{P}_2^{}{}_{}{}^{}$ pairing.

To find the positions and widths of resonances, a complex scaling of the intercluster relative coordinate is introduced into the resonating-group model. In the generator-coordinate technique used to solve the resonating-group equation, the complex scaling requires minor changes in the formulas and code. The finding of the resonances does not need any preliminary guess or explicit reference to any asymptotic prescription. The procedure is applied to the resonances in the relative motion of two ground-state α clusters in ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$, but is appropriate for any systems consisting of two clusters.

Differential cross sections for emission of Z=1 and 2 particles are measured for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ projectiles, with energies between 15 and 25 MeV/nucleon, incident on Al, Ti, Ni, Sn, and Au targets. Integral yields are found to have a complex target mass dependence which, for protons, is consistent with model predictions.

The interaction of 1050 MeV, ${}_{}{}^{84}{}_{}{}^{}\mathrm{Kr}$ ions with natural uranium has been studied with the help of mica track detectors in the 2π configuration. Three ‘‘direct’’ and seven ‘‘indirect’’ events have been observed with four heavy fragments in the exit channel. These events represent a cross section of (16±6) mb for this channel. The correlated tracks of two of the direct events have been used for kinematical analysis. The results indicate a two-step reaction mechanism. In the first step a ‘‘quasifission’’ process takes place which is followed by the sequential fission of at least one of the first step masses.

Differential cross sections for proton-plus-proton elastic scattering at 497.5±0.5 MeV are reported for the center-of-momentum angular range 6°≤${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}\mathrm{\le }97}$°. Statistical and relative point-to-point errors are typically ≤±1% and ≤±2%, respectively. Elastic analyzing powers over the range 16°≤${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}\mathrm{\le }97}$° are also reported. Typical statistical and relative point-to-point uncertainties are ±(0.01–0.03) and ±1%, respectively. Absolute normalization of both the dσ/dΩ and $A_y$ data is obtained through comparison with absolute data from other experiments. Absolute normalization uncertainties are ±2% (cross section) and ±1% (analyzing power). The data are compared with existing data near 500 MeV and with predictions of solutions from phase shift analysis.