Showing papers in "Physical Review C in 1992"

QCD sum rules for vector mesons in the nuclear medium

Abstract: A consistent treatment of quantum chromodynamical (QCD) sum rules in the nuclear medium is developed. Its close relation to the structure functions of the nucleon in the deep inelastic scattering is emphasized. The formalism is applied to the spectral changes of vector mesons (\ensuremath{\rho}, \ensuremath{\omega}, and \ensuremath{\varphi}) in the nuclear matter. A linear decrease of the masses as a function of density is found. The four-quark condensate 〈(q\ifmmode\bar\else\textasciimacron\fi{}q${)}^{2}$〉 and a twist-two condensate 〈q\ifmmode\bar\else\textasciimacron\fi{}${\ensuremath{\gamma}}_{\mathrm{\ensuremath{\mu}}}$q${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathrm{\ensuremath{\mu}}}$${\mathit{D}}_{\ensuremath{ u}}$q〉 in medium play dominant roles for the mass-shift of light mesons. Physical implications of the result in finite nuclei and in heavy ion collisions are also discussed.

Effective interactions for the 0 p 1 s 0 d nuclear shell-model space

Abstract: Shell-model interactions are constructed in the cross-shell model space connecting the 0p and 1s0d shells with due regard for the perturbative effects of the neighboring 0s and 0f1p shells. The interactions have three distinctive 0p-shell, cross-shell, and 1s0d-shell parts. The latter is taken to be the previously determined W interaction. The 0p-shell interaction is represented by two-body matrix elements and the cross-shell by either a potential or by two-body matrix elements. The interactions are determined by least-squares fits to 51 0p-shell and 165 cross-shell binding energies. It is found that the addition of monopole terms to a potential that is otherwise similar to that of the Millener-Kurath interaction results in a great improvement in the fit. In the fit to two-body matrix elements, 45 of 97 possible linear combinations of parameters are varied and the root-mean-square deviation for the 165 cross-shell energies is 330 keV. Examples of the application of the interactions are given for the prediction of neutron-rich binding energies, Gamow-Teller decays, and 0\ensuremath{\Elzxh}\ensuremath{\omega}, 1\ensuremath{\Elzxh}\ensuremath{\omega}, and 2\ensuremath{\Elzxh}\ensuremath{\omega} energy spectra.

Quark and gluon condensates in nuclear matter

Abstract: Quark and gluon condensates in nuclear matter are studied. These in-medium condensates may be linked to a wide range of nuclear phenomena and are important inputs to QCD sum-rule calculations at finite density. The Hellmann-Feynman theorem yields a prediction of the quark condensate that is model independent to first order in the nucleon density. This linear density dependence, with slope determined by the nucleon \ensuremath{\sigma} term, implies that the quark condensate is reduced considerably at nuclear matter saturation density---it is roughly 25--50 % smaller than the vacuum value. The trace anomaly and the Hellmann-Feynman theorem lead to a prediction of the gluon condensate that is model independent to first order in the nucleon density. At nuclear matter saturation density, the gluon condensate is about 5% smaller than the vacuum value. Contributions to the in-medium quark condensate that are of higher order in the nucleon density are estimated with mean-field quark-matter calculations using the Nambu--Jona-Lasinio and Gell-Mann--L\'evy models. Treatments of nuclear matter based on hadronic degrees of freedom are also considered, and the uncertainties are discussed.

Neutron emission as a probe of fusion-fission and quasifission dynamics.

Abstract: Pre-scission and post-scission neutron yields have been measured as a function of projectile mass, compound nucleus fissility, and fission mass split and total kinetic energy (TKE) for 27 fusion-fission and quasifission reactions induced by beams of $^{16,18}\mathrm{O}$, $^{40}\mathrm{Ar}$, and $^{64}\mathrm{Ni}$. A new method of interpretation of experimental pre-scission neutron multiplicities ${\ensuremath{ u}}_{\mathrm{pre}}$ and mean kinetic energies ${\mathrm{\ensuremath{\varepsilon}}}_{\ensuremath{ u}}$ allows the extraction of fission time scales with much less uncertainty than previously, all fusion-fission results being consistent with a dynamical time scale of (35\ifmmode\pm\else\textpm\fi{}15)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ s for symmetric fission. All reactions show that ${\ensuremath{ u}}_{\mathrm{pre}}$ falls quite rapidly with increasing mass asymmetry; evidence is presented that for fusion-fission reactions this is partly due to a reduction of the dynamical fission time scale with mass asymmetry. For quasifission, the data indicate that the pre-scission multiplicity and mean neutron kinetic energy are very sensitive to the final mass asymmetry, but that the time scale is virtually independent of mass asymmetry. It is concluded that for fusion-fission there is no dependence of ${\ensuremath{ u}}_{\mathrm{pre}}$ on TKE, while for $^{64}\mathrm{induced}$ quasifission reactions, a strong increase of ${\ensuremath{ u}}_{\mathrm{pre}}$ with decreasing TKE is observed. This is probably largely caused by neutron emission during the acceleration time of the fission fragments in these fast reactions. Interpretation of post-scission multiplicities in terms of fragment excitation energies leads to deduced time scales consistent with those determined from the pre-scission data.

Simple relation for alpha decay half-lives

Abstract: The experimental values of ${\mathrm{log}}_{10}$${\mathit{T}}_{1/2}$(sec) plotted vs ${\mathit{Z}}_{\mathit{d}}^{0.6}$/ \ensuremath{\surd}${\mathit{Q}}_{\mathrm{\ensuremath{\alpha}}}$ are shown to fall on a nearly universal straight line with ${\mathrm{log}}_{10}$${\mathit{T}}_{1/2}$(sec)=(9.54${\mathit{Z}}_{\mathit{d}}^{0.6}$/ \ensuremath{\surd}${\mathit{Q}}_{\mathrm{\ensuremath{\alpha}}}$)-51.37, where ${\mathit{Z}}_{\mathit{d}}$ is the charge number of the daughter nucleus and ${\mathit{Q}}_{\mathrm{\ensuremath{\alpha}}}$ is expressed in units of MeV. This behavior also numerically comes out of the semiclassical WKB calculation of the barrier penetration factor. The fine structure in the ratio of experiment over theory is briefly discussed.

alpha decay calculations with a realistic potential

Abstract: We have previously used a cluster model, employing a square-well nuclear potential plus a surface-charge Coulomb potential, to satisfactorily describe {alpha}-decay half-lives for more than 400 nuclei. Here, we investigate a more realistic version of this cluster model, in which the square-well nuclear potential is replaced by a cosh'' potential geometry having nonzero diffuseness, and the Coulomb potential by one appropriate to a point charge {alpha} particle interacting with a uniformly charged spherical core. By varying the adjustable parameters of this more realistic model, we find several potentials which give comparable fits to the {alpha}-decay data, and select the one which best tallies with information from other areas of nuclear physics. In addition, we find that the {alpha}-particle preformation probability needed to describe favored transitions in odd-mass nuclei is only 60% of the equivalent quantity required for the ground state to ground state transitions of even-even nuclei.

Relativistic one-boson-exchange model for the nucleon-nucleon interaction.

Abstract: Nucleon-nucleon data below 300-MeV laboratory energy are described by a manifestly covariant wave equation in which one of the intermediate nucleons is restricted to its mass shell. Antisymmetrization of the kernel yields an equation in which the two nucleons are treated in an {ital exactly} symmetric manner, and in which all amplitudes satisfy the Pauli principle {ital exactly}. The kernel is modeled by the sum of one boson exchanges, and four models, all of which fit the data very well ({chi}{sup 2}{congruent}3 per data point) are discussed. Two models require the exchange of {ital only} the {pi}, {sigma}, {rho}, and {omega}, but also require an admixture of {gamma}{sup 5} coupling for the pion, while two other models restrict the pion coupling to pure {gamma}{sup 5}{gamma}{sup {mu}}, but require the exchange of {ital six} mesons, including the {eta}, and a light scalar-isovector meson referred to as {sigma}{sub 1}. Deuteron wave functions resulting from these models are obtained. Th

Nuclear ground state properties in a relativistic point coupling model

Abstract: We present initial results in the calculation of nuclear ground state properties in a relativistic Hartree approximation. Our model consists of Skyrme-type interactions in four-, six-, and eight-fermion point couplings in a manifestly nonrenormalizable Lagrangian, which also contains derivative terms to simulate the finite ranges of the mesonic interactions. A self-consistent procedure has been developed to solve the model equations for several nuclei simultaneously by use of a generalized nonlinear least-squares adjustment algorithm. With this procedure we determine the nine coupling constants of our model so as to reproduce measured ground state binding energies, rms charge radii, and spin-orbit splittings of selected closed major shell and closed subshell nuclei in nondeformed regions. The coupling constants obtained in this way predict these same observables for a much larger set of closed shell spherical nuclei to good accuracy and also predict these quantities for similar nuclei far outside the valley of beta stability. Finally, they yield properties of saturated nuclear matter in agreement with recent relativistic mean meson field approaches.

Variational calculation of the ground state of O 16

Abstract: We report variational calculations of the ground state of $^{16}\mathrm{O}$ with realistic two- and three-nucleon interactions. The trial wave function is constructed from pair- and triplet-correlation operators acting on a product of single-particle determinants. These operators include central, spin, isospin, tensor, spin-orbit, and three-nucleon potential components. Expectation values are evaluated with a cluster expansion for the noncentral correlations; terms in the expansion are evaluated exactly using Monte Carlo integration. The optimal trial function is obtained by minimizing the energy through the four-body cluster level. Results are reported for the ground-state binding energy, nucleon density and momentum distributions, charge form factor, and longitudinal structure function. They are also compared with the available results for few-body nuclei and nuclear matter with the same interactions.

Metastable Exotic Multihypernuclear Objects

Abstract: When one is looking at the area of normal nuclei one knows for a very long time that there exists a valley of stability and that the binding energy can be well described by the Bethe-Weizsacker formula. Nowadays, it is assumed that QCD is the underlying basic theory. If one studies another degree of freedom of QCD, the strangeness, one realizes that this opens a new dimension of finite nuclear systems. Hence, one has to deal with a three dimensional space of nuclear composites of nucleons and hyperons.

Near-barrier fusion of Li 11 with heavy spherical and deformed targets

Abstract: The cross sections for the fusion of $^{11}\mathrm{Li}$ with $^{208}\mathrm{Pb}$ and $^{238}\mathrm{U}$ are calculated at near-barrier energies. The coupling of the entrance channel to the soft giant dipole resonance in $^{11}\mathrm{Li}$ is taken into account together with the coupling to the breakup channel $^{9}\mathrm{Li}$+2n. The deformation of $^{238}\mathrm{U}$ is also considered. The cross section is found to exhibit important structure around the barrier.

Nuclear transparency to intermediate-energy nucleons from ( e , e ’ p ) reactions

Abstract: A simple relation between the nucleon-nucleon scattering cross sections in vacuum and in nuclear matter is proposed It consistently takes into account the velocity dependence of the nuclear mean field and Pauli blocking, and is shown to be fairly accurate It is used to study the mean free path of nucleons in nuclear matter and the imaginary part of the optical potential It is also used with the local density approximation and the correlated Glauber approximation to calculate the transparency of nuclei as measured by (e,e'p) reactions The Pauli blocking, velocity dependence of the nuclear mean field, and the ground-state correlations increase the transparency, and all the three effects are necessary to explain the observed transparencies of $^{12}\mathrm{C}$, $^{27}\mathrm{Al}$, $^{58}\mathrm{Ni}$, and $^{181}\mathrm{Ta}$ for recoiling 180 MeV protons

Resolution of nuclear ground and isomeric states by a Penning trap mass spectrometer.

Abstract: Ground and isomeric states of a nucleus have been resolved for the first time by mass spectrometry. Measurements on $^{78}\mathrm{Rb}^{\mathit{m},}$g and $^{84}\mathrm{Rb}^{\mathit{m},}$g were performed using a tandem Penning trap mass spectrometer on-line with the isotope separator ISOLDE/CERN. The effects of ion-ion interaction were investigated for two ion species differing in mass and stored simultaneously in the trap.

Hyperon electroproduction in a crossing and duality constrained model.

Abstract: Using our previously developed crossing and duality consistent model for kaon photoproduction and radiative capture, we investigate the kaon electroproduction processes p(e,e'${\mathit{K}}^{+}$)Y for Y=\ensuremath{\Lambda}, ${\mathrm{\ensuremath{\Sigma}}}^{0}$, and \ensuremath{\Lambda}(1405). Because there is no electroproduction data near threshold, consistency requires extending the energy range of our photoproduction model parametrization from an upper bound of ${\mathit{E}}_{\ensuremath{\gamma}}^{\mathrm{lab}}$=1.4 to 2.2 GeV. We find that baryon resonances with spin greater than 1/2 are necessary to describe the higher energy photoproduction data (1.4\ensuremath{\le}${\mathit{E}}_{\ensuremath{\gamma}}^{\mathrm{lab}}$\ensuremath{\le}2.2 GeV). We also extend our use of duality by representing these higher-spin s- and u-channel baryon resonances with the low-lying t-channel vector, ${\mathit{K}}^{\mathrm{*}}$(890), and pseudovector, ${\mathit{K}}_{1}$(1270), mesons. Using this extended crossing and duality consistent model, we obtain reasonable agreement with the data for both photoproduction and electroproduction processes.

Neutron stars in the derivative coupling model.

Abstract: Properties of neutron stars derived from the hybrid derivative coupling model of nuclear field theory are studied. Generalized beta equilibrium with all baryon types to convergence is allowed. Hyperon couplings compatible with the inferred binding energy of the lambda hyperon in saturated nuclear matter predict a large hyperon population, with neutrons having a bare majority population in a 1.5{ital M}{sub {circle dot}} neutron star. Among the properties studied are the limits on rotation imposed by gravitation-radiation-reaction instabilities as moderated by viscosity. These instabilities place a lower limit on rotational periods of neutron and hybrid stars of about 1 ms.

Properties of dense nuclear and neutron matter with relativistic nucleon-nucleon interactions

Abstract: Within the framework of the Dirac-Brueckner (DB) approach, the properties of dense nuclear and neutron matter are investigated using realistic nucleon-nucleon (NN) interactions which are derived from relativistic meson-field theory and describe the two-nucleon system quantitatively. Single-particle potentials, equations of state, nucleon effective masses, Landau parameters, and speeds of sound are calculated and analyzed as functions of density, for both nuclear and neutron matter. In the DB approach, the equation of state comes out stiffer than in the most sophisticated nonrelativistic calculation, but softer than in the Walecka model. Possible extensions of the present approach to nucleon-nucleus scattering and nucleus-nucleus collisions are also discussed.

Double beta decay of 82Se.

Abstract: Pairs of negative beta particles have been observed originating from a $^{82}\mathrm{Se}$ source during a cloud-chamber search for double beta decay. Backgrounds recognized in previous experiments were suppressed to well below the observed event rate, and no other significant backgrounds are apparent. Within the limited statistics of the small data sample, the observed single-electron energy spectrum, the two-electron sum energy spectrum, and the opening angle distribution are consistent with expectation for neutrino-accompanied double beta decay of $^{82}\mathrm{Se}$. The tentative assignment of the observed events to double beta decay, results in a $^{82}\mathrm{Se}$ half-life of (1.0\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}${10}^{19}$ years, in good agreement with some very recent theoretical predictions. However, the result is in serious disagreement with the much longer half-lives measured in geochemical experiments. A planned follow-up experiment is described.RADIOACTIVITY $\ensuremath{\beta}\ensuremath{\beta}$-decay $^{82}\mathrm{Se}$; measured ${I}_{\ensuremath{\beta}\ensuremath{\beta}}$; deduced ${T}_{\frac{1}{2}}$.

QCD sum rules for nucleons in nuclear matter

Abstract: The self-energies of quasinucleon states in nuclear matter are investigated using a finite-density QCD sum-rule approach developed previously. The sum rules are obtained for a general QCD interpolating field for the nucleon. The key phenomenological inputs are the nucleon \ensuremath{\sigma} term, the strangeness content of the nucleon, and quark and gluon distribution functions deduced from deep-inelastic scattering. The emphasis is on testing the sensitivity and stability of sum-rule predictions to variations of the condensates and other input parameters. At nuclear matter saturation density, the Lorentz vector self-energy is found to be positive with a magnitude of a few hundred MeV, which is comparable to that suggested by relativistic nuclear phenomenology. This result is quite stable. The prediction for the scalar self-energy is very sensitive to the undertermined values of the in-medium four-quark condensates.

Double-beta decay to excited 0(+) states: Decay of 100Mo.

Abstract: We develop a formalism for describing the 2\ensuremath{ u} mode of double-beta decay to an excited final state in the quasiparticle random phase approximation (QRPA). With this, we deduce the half-lives for the $^{100}\mathrm{Mo}$ double-beta decays to both the ground and 1130 keV excited ${0}^{+}$ states in $^{100}\mathrm{Ru}$. We predict the matrix elements of these two transitions to be of a similar magnitude. We also calculate the strengths of the associated single-beta decays from the ground state of the intermediate nucleus, $^{100}\mathrm{Tc}$, and compare them with experiment. We find that the QRPA cannot simultaneously reproduce all of the experimental quantities, and, in particular, the single-beta transition between the initial and intermediate nuclei is overestimated by the theory. In addition, we demonstrate that the influence of the particle-particle force is an important factor in the calculation of both ${\mathrm{\ensuremath{\beta}}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{\ensuremath{\beta}}}^{+}$ transition strengths.

Blast of light fragments from central heavy-ion collisions

Abstract: The effects of collective expansion on light-fragment emission from central heavy-ion collisions are studied by carrying out calculations in a transport model with dynamic production of {ital A}{le}3 fragments. Beam energies of few hundred MeV/nucleon are considered. In the simulations the formation of a region of dense excited nuclear matter is observed, which expands in transverse directions. The expansion is reflected in the angular distributions and in the mean transverse energies of emitted fragments. At the late stage of expansion the characteristic features of local thermodynamic equilibrium are identified. Different particles share nearly the same collective energy per nucleon, and nearly the same thermal energy. The calculated mean transverse energies of the fragments reflect the collective energy whose magnitude varies with impact parameter. However, the fragment energies only partially agree with available data. The calculated spectra exhibit different slopes at angles around c.m. 90{degree} in central reactions.

Fusion barriers using the energy-density formalism: Simple analytical formula and the calculation of fusion cross sections

Abstract: Fusion barriers are calculated within the sudden approximation, using the Skyrme interaction energy-density model. Both the closed and unclosed shell nuclei are considered and the role of spin-density term is studied in detail. For unclosed shell nuclei, the fusion cross sections are found to decrease by as much as {similar to}50 mb when spin-density effects are included. Very accurate, simple analytical expressions, in terms of only the masses and charges of the reacting nuclei, are obtained for the barrier heights and positions. This introduces a great simplification for the fusion barrier calculations.

Generalized potential-model description of mutual scattering of the lightest p+d, d+ 3 He nuclei and the corresponding photonuclear reactions

Abstract: For the problem of interaction between the lightest {ital p}+{ital d}, d+{sup 3}He nuclei supermultiplet expansion of the reaction amplitude {ital T}{sub {ital L}{ital S}} is proposed. We have disclosed the nonpotential character of channels with {ital S}=1/2, where the scattering amplitude is written as a superposition of the potential amplitudes {ital T}{sub {ital L}}{sup ({ital f})} with different symmetries ({ital f}). We have constructed the interaction potentials {ital V}{sub {ital L}}{sup ({ital f})}, ({ital f})=(21), (3) and ({ital f})=(32), (41) for {ital p}+{ital d} and {ital d}+{sup 3}He, respectively. The differential cross sections for {ital p}+{ital d} inelastic scattering with the deuteron spin-isospin flip, which correspond to the available experimental data in the low-energy region, are predicted at higher energies and also for the {ital d}+{sup 3}He system in a broad energy interval. The potential-model approach well describes quantitatively the photonuclear {sup 3}He{gamma}{r arrow}{ital p}+{ital d} and {ital d}+{sup 3}He{r arrow}{sup 5}Li {gamma} processes in a broad photon energy range {ital E}{sub {gamma}}{le}30 MeV.

Proton propagation in nuclei studied in the (e , e 'p) reaction

Abstract: Proton propagation in nuclei was studied using the ({ital e},{ital e}{prime}{ital p}) reaction in the quasifree region. The coincidence ({ital e},{ital e}{prime}{ital p}) cross sections were measured at an electron angle of 50.4{degree} and proton angles of 50.1{degree}, 58.2{degree}, 67.9{degree}, and 72.9{degree} for {sup 12}C, {sup 27}Al, {sup 58}Ni, and {sup 181}Ta targets at a beam energy of 779.5 MeV. The average outgoing proton energy was 180 MeV. The ratio of the ({ital e},{ital e}{prime}{ital p}) yield to the simultaneously measured ({ital e},{ital e}{prime}) yield was compared to that calculated in the plane-wave impulse approximation and an experimental transmission defined. These experimental transmissions are considerably larger (a factor of {similar to}2 for {sup 181}Ta) than those one would calculate from the free {ital N}-{ital N} cross sections folded into the nuclear density distribution. A new calculation that includes medium effects ({ital N}-{ital N} correlations, density dependence of the {ital N}-{ital N} cross sections and Pauli suppression) accounts for this increase.

Atomic parity nonconservation: Electroweak parameters and nuclear structure

Abstract: There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic-structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the standard model at the level of one-loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and nonrelativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear-structure effects may preclude using Pb isotope ratios to test the standard model at better than a 1% level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei.

Effect of the neutron skin on collective states of nuclei.

Abstract: The effect of a neutron skin on the collective states of medium and heavy-mass nuclei is discussed. We consider two well-known collective modes which correspond to the motion of neutrons with respect to protons, namely, the M1 (scissors) and the isovector E1 (giant dipole) resonance. For nuclei with a sufficient excess of neutrons the behavior of the ``pygmy resonance'' is also discussed.

Rho meson in dense hadronic matter

Abstract: The spectral function of a rho meson that is at rest in dense hadronic matter and couples strongly to the pion is studied in the vector dominance model by including the effect of the delta-hole polarization of the pion. With the free rho-meson mass in the Lagrangian, we find that both the rho-meson peak and width increase with increasing nuclear density, and that a low-mass peak appears at invariant mass around three times the pion mass. Including the decreasing density-dependent hadron masses in the Lagrangian as suggested by the scaling law of Brown and Rho, we find instead that the rho peak moves to smaller invariant masses with diminishing strength when the nuclear density increases. The low-mass peak also shifts down with increasing density and becomes more pronounced. The relevance of the rho-meson property in dense matter to delepton production in heavy-ion collisions is discussed.

Systematic study of low-spin states in even Cd nuclei.

Abstract: Low-lying low-spin collective states in even $^{106\mathrm{\ensuremath{-}}112}\mathrm{Cd}$ and $^{116}\mathrm{Cd}$ were investigated using in-beam and off-beam \ensuremath{\gamma}-ray and conversion-electron spectroscopy. New spin assignments and decay branching ratios for the levels in $^{106}\mathrm{Cd}$, $^{108}\mathrm{Cd}$, $^{110}\mathrm{Cd}$, and $^{112}\mathrm{Cd}$ were obtained. The present results essentially complement the level systematics from $^{106}\mathrm{Cd}$ to $^{120}\mathrm{Cd}$. From the new data, it is inferred that two sets of low-lying ${0}^{+}$ states having different excitation characteristics cross between $^{114}\mathrm{Cd}$ and $^{116}\mathrm{Cd}$. No corresponding crossing occurs on the neutron deficient side. New evidence for the existence of the proton-intruder states has been found.

Intermediate mass fragment emission in 36Ar+197Au collisions at E/A=35 MeV.

Abstract: Intermediate mass fragment (IMF: 3{le}{ital Z}{le}20) emission for the {sup 36}Ar+{sup 197}Au reaction at {ital E}/{ital A}=35 MeV has been studied with a low-threshold 4{pi} charged-particle detector array covering the angular range of 16{degree}{le}{theta}{sub lab}{le}160{degree}. While most IMF's are emitted in central collisions characterized by large charged-particle multiplicities, contributions from peripheral collisions exist at forward angles which are reminiscent of damped collisions or emission from a projectile-like source. Energy spectra, angular distributions, element distributions, and two-fragment correlation functions are presented for various gates on the charged-particle multiplicity, and the time scale of fragment emission is deduced.

Electron Coulomb effects in quasielastic (e,e'p) reactions.

Abstract: We describe a calculation for the electron Coulomb distortion effects in ({ital e},{ital e}{prime}{ital p}) in the quasielastic region from medium and heavy nuclei. The bound nucleons are described by single-particle Dirac wave functions in the presence of scalar and vector potentials which are parametrized fits to relativistic Hartree potentials, while the wave function of the knocked-out nucleon is a solution to the Dirac equation with the relativistic optical potential. The electron wave functions are solutions to the Dirac equation in the presence of the Coulomb potential of the nucleus and the interaction with the selected nucleon is treated to first order. We examine the {sup 40}Ca({ital e},{ital e}{prime}{ital p}) reaction in both parallel and {omega}-{ital q} constant kinematics. We find that electron Coulomb distortion has a smaller effect in {omega}-{ital q} constant kinematics than in parallel kinematics. The principal effect in parallel kinematics is to shift the maximum and minimum of the reduced cross section which is consistent with the experimental data. Occupation numbers of about 70% to 80% are needed to normalize the distorted-wave Born approximation calculation to the {sup 40}Ca({ital e},{ital e}{prime}{ital p}) experimental data. We also calculate the reduced cross section for the 3{ital s}{sub 1/2}more » state in {sup 208}Pb and compare our results to experimental data and previous calculations. We find no significant difference in using relativistic, as compared with nonrelativistic, nuclear wave functions. We do find significant corrections to earlier methods of treating Coulomb distortion which, in turn, affect the occupation number extracted from experiment. We find an occupation number for this state of 71.4%.« less

Level spin for superdeformed nuclei near A =194

Abstract: Transition energies of 25 superdeformed (SD) bands in 13 nuclei of the A=194 region were fitted by the power-series expansion of I in odd powers of ${\mathit{E}}_{\ensuremath{\gamma}}$/2, \ensuremath{\Elzxh}(I+1/2)=2\ensuremath{\alpha}\ensuremath{\omega}+4/3\ensuremath{\beta}${\mathrm{\ensuremath{\omega}}}^{3}$, where ${\mathit{E}}_{\ensuremath{\gamma}}$/2=\ensuremath{\Elzxh}\ensuremath{\omega}, and by the expression for transition energy, ${\mathit{E}}_{\ensuremath{\gamma}}$=E(I+2)-E(I), where E(I)=AI(I+1) +B[I(I+1)${]}^{2}$+C[I(I+1)${]}^{3}$. Results are generally similar, and level spins for these SD bands are given based on expectations of rotational model behavior.