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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Collisions induced by halo and weakly bound nuclei around the Coulomb barrier: Results at INFN-LNS Catania

The study of collisions around the Coulomb barrier induced by halo and/or weakly bound nuclei has been the object of many publications in the last years, since the peculiar structure of such nuclei can strongly affect the reaction dynamics. In this paper we will summarize some results on the above topic obtained by our group at INFN-LNS Catania. Results concerning the study of elastic scattering and different reaction mechanisms in collisions induced by the halo nuclei {sup 11}Be and {sup 6}He and by the weakly bound stable nuclei {sup 6,7}Li on a {sup 64}Zn target, at energies around the Coulomb barrier, will be presented. The conclusions of our studies will be compared with the ones of other authors, in order to show if clear systematic conclusions can be drawn from the different papers published in the literature so far.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Core excitation effects in halo nuclei using a transformed oscillator basis

A recent generalization of the Transformed Harmonic Oscillator basis, intended to consider core excitations in the structure of one nucleon halo nuclei, is applied to the break up of {sup 11}Be. The reaction studied is {sup 11}Be+{sup 208}Pb at 69 MeV/nucleon. The experimental set up is designed to ensure pure dipole Coulomb excitations. Making use of the Equivalent Photon Method and the electromagnetic transition probabilities obtained with the transformed oscillator basis, a relevant contribution of the quadrupole excitations of the core is found. The inclusion of core excitations is, therefore, necessary for the correct extraction of the dipole electromagnetic transition probability of halo nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Structure of the spatial periphery of the {sup 11}Li and {sup 11}Be isobars

On the basis of the shell model with an extended basis, the structure of {sup 9}Li-{sup 9}Be to {sup 11}Li-{sup 11}Be nuclei is examined with allowance for the competition of {sup jj} coupling and Majorana exchange forces via considering the sequential addition of neutrons, and the respective wave functions are determined. A formalism for calculating the spectroscopic factor for a dineutron and for individual neutrons in nuclei whose wave functions incorporate the mixing of shell configurations is developed. The reactions {sup 9}Li(t, p){sup 11}Li and {sup 9}Be(t, p){sup 11}Be treated with allowance for the mechanisms of dineutron stripping and a sequential transfer of two neutrons are considered as an indicator of the proposed structure of lithium and berylliumisotopes. The parameters of the optical potentials, the wave functions for the bound states of transferred particles, and the interaction potentials corresponding to them are determined from a comparison of the theoretical angular distribution of protons from the reaction {sup 9}Be(t, p){sup 11}Be with its experimental counterpart. It is shown that a dineutron periphery of size about 6.4 fm is present in the {sup 11}Li nucleus and that a single-neutron periphery of size about 8 fm is present in the {sup 11}Be nucleus.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Nuclear states with anomalously large radius (size isomers)

Methods of determination of the nuclear excited state radii are discussed together with the recently obtained data on the states of some light nuclei having abnormally large radii (size isomers). It is shown that such states include excited neutron-halo states in {sup 9}Be, {sup 11}Be, and {sup 13}C and some alpha-cluster states in {sup 12}C, {sup 11}B, and {sup 13}C. Among the latter ones, there is the well-known Hoyle state in {sup 12}C—the structure of this state exhibit rudimentary features of alpha-particle states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Neutron widths and configuration mixing in {sup 11}Be

We use known widths and branching ratios in {sup 11}Be to discuss J{sup {pi}} and configuration admixtures. Analysis favors 3/2{sup -} for the 3.96-MeV state and three-state mixing for this J{sup {pi}}.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Exploring continuum structures with a pseudo-state basis

The ability of a recently developed square-integrable discrete basis to represent the properties of the continuum of a two-body system is investigated. The basis is obtained performing a simple analytic local scale transformation to the harmonic oscillator basis. Scattering phase-shifts and the electric transition probabilities B(E1) and B(E2) have been evaluated for several potentials using the proposed basis. Both quantities are found to be in excellent agreement with the exact values calculated from the true scattering states. The basis has been applied to describe the projectile continuum in the {sup 6}He scattering by {sup 12}C and {sup 208}Pb targets at 240 MeV/nucleon and the {sup 11}Be scattering by {sup 12}C at 67 MeV/nucleon. The calculated breakup differential cross sections are found to be in very good agreement with the available experimental data for these reactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Strong nuclear couplings as a source of Coulomb rainbow suppression

A recent measurement of the {sup 11}Be+{sup 64}Zn quasielastic scattering angular distribution exhibits a non-Fresnel-type pattern, in contrast to {sup 6}He+{sup 64}Zn elastic scattering but similar to that for the elastic scattering of {sup 6}He from heavy targets. We show by means of continuum discretized coupled-channels (CDCC) calculations that this unusual behavior of {sup 11}Be is caused by the much greater importance of nuclear coupling to the continuum in {sup 11}Be compared to {sup 6}He, where Coulomb dipole coupling is mainly responsible for the non-Fresnel-like shape, when present. We also show that the dynamic polarization potentials derived from the CDCC calculations seem to follow a universal form as a function of radius.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Study Of The Scattering Of Halo Nuclei Around The Coulomb Barrier

During the past ten years the present collaboration has carried out several experiments related with the study of radioactive nuclei. One of the topics in which we have centered our research, is the scattering of halo nuclei at energies around the Coulomb barrier. As part of this study, we present in this work a review of the results obtained from the scattering of {sup 6}He, {sup 11}Be and {sup 11}Li. The presence of a ''halo'' in these exotic nuclei is found to have a striking effect on the dynamics of these reactions, making their study an interesting experimental problem and a challenge for existing reaction theories.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Observation of abnormally large radii of nuclei in excited states in the vicinity of neutron thresholds

Differential cross sections for inelastic scattering leading to the excitation of some nuclear states situated near neutron-emission thresholds were analyzed. With the aid of a modified diffraction model, abnormally large radii were found for the 1/2{sub 1}{sup +} state of the {sup 13}C nucleus at 3.09 MeV, for the first levels of positive-parity rotational bands in the {sup 9}Be (1/2{sup +} level at 1.68 MeV and 5/2{sup +} level at 3.05 MeV) and {sup 11}Be (5/2{sup +} level at 1.78 MeV and 3/2{sup +} level at 3.41 MeV) nuclei, and for the 2{sub 1}{sup +} state of the {sup 14}Be nucleus at 1.54 MeV and 1{sub 1}{sup -} state of the {sup 12}Be nucleus at 2.7 MeV. All of these states possess signatures typical of neutron halos.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Deducing spectroscopic factors from wave-function asymptotics

In a coupled-channel model, we explore the effects of coupling between configurations on the radial behavior of the wave function and, in particular, on the spectroscopic factor (SF) and the asymptotic normalization coefficient (ANC). We evaluate the extraction of a SF from the ratio of the ANC of the coupled-channel model to that of a single-particle approximation of the wave function. We perform this study within a core+n collective model, which includes two states of the core that connect by a rotational coupling. To get additional insights, we also use a simplified model that takes a {delta} function for the coupling potential. Calculations are performed for {sup 11}Be. Fair agreement is obtained between the SF inferred from the single-particle approximation and the one obtained within the coupled-channel models. Significant discrepancies are observed only for large coupling strength and/or large admixture, that is, a small SF. This suggests that reliable SFs can be deduced from the wave-function asymptotics when the structure is dominated by one configuration, that is, for a large SF.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Neutron knockout of {sup 12}Be populating neutron-unbound states in {sup 11}Be

Neutron-unbound resonant states of {sup 11}Be were populated in neutron knockout reactions from {sup 12}Be and identified by {sup 10}Be-n coincidence measurements. A resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly excited unbound state in {sup 11}Be at 3.949(2) MeV decaying to the 2{sup +} excited state in {sup 10}Be. A knockout cross section of 15(3) mb was inferred for this 3.949(2) MeV state, suggesting a spectroscopic factor near unity for this 0p3/2{sup -} level, consistent with the detailed shell model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Core excitation contributions to the breakup of the one-neutron halo nucleus {sup 11}Be on a proton

The effect of the core excitation in the breakup of a one-neutron halo nucleus is studied within two different reaction formalisms, namely, the core excited model and the single-scattering approximation of the three-body Faddeev-Alt-Grassberger-Sandhas equations with target-core potential allowing for the core excitation. As an example, we consider the breakup of {sup 11}Be on a proton target at 63.7 MeV/nucleon incident energy and calculate the semi-inclusive cross section in the excitation energy interval E{sub x}=3.0-5.5 MeV (E{sub rel}=2.5-5 MeV) containing the 3/2{sup +} resonance with dominant contribution of the {sup 10}Be(2{sup +}) core excited state. The effect of the core excitation to the breakup cross section integrated around this resonance is found to be very significant. Moreover, when resonant and nonresonant contributions are added, the resulting semi-inclusive cross section is in reasonable agreement with the existing data, demonstrating the relevance of the core excitation mechanism for this observable. The present calculations also show the importance of incorporating the energy dependence of the core-target transition operators in the reaction formalism.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Measurement of the {sup 8}B solar neutrino flux with the KamLAND liquid scintillator detector

We report a measurement of the neutrino-electron elastic scattering rate from {sup 8}B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5-MeV analysis threshold is 1.49 {+-} 0.14(stat) {+-} 0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a {sup 8}B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77 {+-} 0.26(stat) {+-} 0.32(syst) x10{sup 6} cm{sup -2}s{sup -1}. The analysis threshold is driven by {sup 208}Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic {sup 11}Be. The measured rate is consistent with existing measurements and with standard solar model predictions which include matter-enhanced neutrino oscillation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Photoproduction of {pi}{sup +}p pairs on nuclei

The photoproduction of pion-nucleon pairs on nuclei was analyzed. The contributions of both nucleonic and isobar configurations in the ground state of nuclei were taken into account. The cross section for the photoproduction of pion-proton pairs in the reactions {sup 16}O({gamma}, {pi}{sup +}p){sup 15}C and {sup 12}C({gamma}, {pi}{sup +}p){sup 11}Be were calculated.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

On the implementation of a chain nuclear reaction of thermonuclear fusion on the basis of the p+{sup 11}B process

Various theoretical and experimental schemes for implementing a thermonuclear reactor on the basis of the p+{sup 11}B reaction are considered. They include beam collisions, fusion in degenerate plasmas, ignition upon plasma acceleration by ponderomotive forces, and the irradiation of a solid-state target from {sup 11}B with a proton beam under conditions of a Coulomb explosion of hydrogen microdrops. The possibility of employing ultra-short high-intensity laser pulses to initiate the p+{sup 11}B reaction under conditions far from thermodynamic equilibrium is discussed. This and some other weakly radioactive thermonuclear reactions are promising owing to their ecological cleanness—there are virtually no neutrons among fusion products. Nuclear reactions that follow the p+{sup 11}B reaction may generate high-energy protons, sustaining a chain reaction, and this is an advantage of the p+{sup 11}B option. The approach used also makes it possible to study nuclear reactions under conditions close to those in the early Universe or in the interior of stars.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Possibility of Studying Neutron–Neutron Correlations in Halo Nuclei

An experimental investigation of the reaction of core pickup from {sup 6}He and {sup 11}Li two-neutronhalo nuclei is proposed. In such experiments, neutron–neutron correlations in a halo nucleus will be assessed on the basis of the energy of a neutron–neutron quasibound state. A detailed kinematical simulation of the reaction {sup 6}He + {sup 2}H → {sup 6}Li + (nn) →{sup 6} Li + n + n is performed. It is shown that the energy of the quasibound state in question can determined from the shape of the energy spectrum of neutrons originating from the breakup of this state. In the proposed exclusive experiment, a beam of {sup 6}He ({sup 11}Li) nuclei with an energy of about 5 to 10 MeV per nucleon interacts with a deuterated-polyethylene target. This will permit detecting charged particles ({sup 6}Li and {sup 11}Be) and a neutron. On the basis of determining the energy of the neutron–neutron quasibound state, it will become possible to estimate the effective attraction between the valence neutrons in the field of the third particle (core).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Cosmogenic Backgrounds in Borexino at 3800 m water-equivalent depth

The solar neutrino experiment Borexino, which is located in the Gran Sasso underground laboratories, is in a unique position to study muon-induced backgrounds in an organic liquid scintillator. In this study, a large sample of cosmic muons is identified and tracked by a muon veto detector external to the liquid scintillator, and by the specific light patterns observed when muons cross the scintillator volume. The yield of muon-induced neutrons is found to be Y{sub n} = (3.10±0.11)·10{sup −4} n/(μ·(g/cm{sup 2})). The distance profile between the parent muon track and the neutron capture point has the average value λ = (81.5±2.7) cm. Additionally the yields of a number of cosmogenic radioisotopes are measured for {sup 12}N, {sup 12}B, {sup 8}He, {sup 9}C, {sup 9}Li, {sup 8}B, {sup 6}He, {sup 8}Li, {sup 11}Be, {sup 10}C and {sup 11}C. All results are compared with Monte Carlo simulation predictions using the FLUKA and GEANT4 packages. General agreement between data and simulation is observed for the cosmogenic production yields with a few exceptions, the most prominent case being {sup 11}C yield for which both codes return about 50% lower values. The predicted μ-n distance profile and the neutron multiplicity distribution are found to be overall consistent with data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗