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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Fusion cross sections for the {sup 9}Be+{sup 124}Sn reaction at energies near the Coulomb barrier

The complete and incomplete fusion cross sections for {sup 9}Be+{sup 124}Sn reaction have been deduced using the online {gamma}-ray measurement technique. Complete fusion at energies above the Coulomb barrier was found to be suppressed by {approx}28% compared to the coupled-channels calculations and is in agreement with the systematics of L. R. Gasques et al. [Phys. Rev. C 79, 034605 (2009)]. Study of the projectile dependence for fusion on a {sup 124}Sn target shows that, for {sup 9}Be nuclei, the enhancement at below-barrier energies is substantial compared to that of tightly bound nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Reaction dynamics for the system {sup 17}F+{sup 58}Ni at near-barrier energies

Charged reaction products originated from the interaction of the loosely bound radioactive ion beam {sup 17}F (S{sub p}=600 keV) with the proton-shell closed {sup 58}Ni target were measured at two colliding energies slightly above the Coulomb barrier. The collected data were analyzed within the framework of the optical model to deduce the reaction cross section and to investigate the role played by inelastic excitations, transfer channels, and the breakup process {sup 17}F{yields}{sup 16}O+p at near-barrier energies. The reaction cross section at the lower {sup 17}F energy showed a moderate enhancement ({approx}20%) with respect to that of the system {sup 16}O+{sup 58}Ni. At this energy direct reaction channels were also found to be more relevant than those for the reaction induced from the tightly bound projectile {sup 16}O on the same target. Both features could be strongly related to the very low binding energy of the {sup 17}F valence proton.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Coupled-channels density-matrix approach to low-energy nuclear collision dynamics: A technique for quantifying quantum decoherence effects on reaction observables

The coupled-channels density-matrix technique for nuclear reaction dynamics, which is based on the Liouville-von Neumann equation with Lindblad dissipative terms, is developed with the inclusion of full angular momentum couplings. It allows a quantitative study of the role and importance of quantum decoherence in nuclear scattering. Formulas of asymptotic observables that can reveal effects of quantum decoherence are given. A method for extracting energy-resolved scattering information from the time-dependent density matrix is introduced. As an example, model calculations are carried out for the low-energy collision of the {sup 16}O projectile on the {sup 154}Sm target.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Quantum tunneling and scattering of a composite object reexamined

This work presents an extensive exploration of scattering and tunneling involving composite objects with intrinsic degrees of freedom. We aim at exact solutions to such scattering problems. Along this path we demonstrate solutions to model Hamiltonians and develop different techniques for addressing these complex reaction-physics problems, discuss their applicability, and investigate the relevant convergence issues. As examples, we study the scattering of two-constituent deuteron-like systems either with an infinite set of intrinsic bound states or with a continuum of states that allows for breakup. We show that the internal degrees of freedom of the projectile and its virtual excitation in the course of reactions play an important role in shaping the S-matrix and related observables, giving rise to enhanced or reduced tunneling in various situations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Production of neutron-rich Ca, Sn, and Xe isotopes in transfer-type reactions with radioactive beams

The production cross sections of neutron-rich isotopes {sup 52,54,56,58,60}Ca, {sup 136,138,140,142}Sn, and {sup 146,148,150,152}Xe are predicted for future experiments in the diffusive multinucleon transfer reactions {sup 86,90,92,94}Kr, {sup 124,130,132,134}Sn, {sup 136,140,142,146}Xe, and {sup 138,144,146}Ba+{sup 48}Ca with stable and radioactive beams at incident energies close to the Coulomb barrier. Because of the small cross sections, the production of neutron-rich isotopes requires the optimal choice of projectile-target combinations and bombarding energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Two-nucleon correlation effects in knockout reactions from {sup 12}C

Reactions that involve the direct and sudden removal of a pair of like or unlike nucleons from a fast projectile beam by a light target nucleus are considered. Specifically, we study the three two-nucleon removal channels from {sup 12}C that populate final states in the {sup 10}Be, {sup 10}B, and {sup 10}C reaction residues. The calculated two-nucleon removal cross sections and the residue momentum distributions are compared with available high-energy data at 250, 1050, and 2010 MeV per nucleon, i.e., data that are inclusive with respect to the bound final states of the residues. The measured np removal cross sections only are significantly greater than the values calculated, suggesting that the reaction mechanism observes enhanced np spatial correlations compared to those present in the shell-model wave functions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Odd-even effect in heavy-ion collisions at intermediate energies

Heavy-ion collisions at intermediate energies are studied by the isospin-dependent quantum molecular dynamics model in the company of the GEMINI model. The isospin-dependent quantum molecular dynamics model is applied to describe the violent stage of the collisions, while the GEMINI model is applied to simulate the decays of the prefragments. The present study mainly focuses on the odd-even effect in the yields of the final fragments. We find that the odd-even effect appears in the deexcitation process of the excited prefragments, and is affected by the excitation energies and the isotope distributions of the prefragments. Both the projectile-isospin-dependent odd-even effect in the region of -4{<=}T{sub Z}{<=}1 and the role of the symmetry energy on the odd-even effect are studied. We find that the odd-even effect depends sensitively on the symmetry energy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Systematics of reactions with {sup 4,6}He: Static and dynamic halo effects and evidence for core-halo decoupling

Experimental reaction cross sections for {sup 6}He and {sup 4}He projectiles are reduced and are shown to follow well-defined trajectories that can be characterized by respective Wong-type curves. The strong enhancement observed for the {sup 6}He data is interpreted as caused by two separate halo effects: a size effect, which affects the whole energy region, and a dynamic effect, important only near and below the barrier. Evidence for a core-halo decoupling is presented for the {sup 6}He+{sup 64}Zn system, which further supports the hypothesis that the decoupling is a characteristic feature of true halo systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Breakup threshold anomaly in the near-barrier elastic scattering of {sup 6}Li+{sup 116,112}Sn

We have measured the elastic scattering of the weakly bound {sup 6}Li on the {sup 116,112}Sn targets, at energies close to the Coulomb barrier. The energy dependence of the interaction potential has been investigated by two different methods and the presence of the breakup threshold anomaly is observed. We have also derived the total reaction cross sections for the above systems and compared them to those of other systems with halo, weakly bound, and tightly bound projectiles on targets with similar masses. The reaction cross sections are largest for systems with halo nuclei, then the systems with no-halo weakly bound nuclei, and the smallest cross sections are those for tightly bound systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Reaction mechanisms involving weakly bound {sup 6}Li and {sup 209}Bi at energies near the Coulomb barrier

The elastic, inelastic, and transfer cross sections are measured for the {sup 6}Li+{sup 209}Bi reaction at energies around the Coulomb barrier. The optical model analysis of elastic scattering shows a breakup threshold anomaly in the energy dependence of the real and imaginary potentials. The observed energy dependence is found to be consistent with the dynamic polarization potential obtained from the coupled-channels calculations that explain the above measured reaction channels simultaneously. A comparison of different reaction probabilities reveals that the relative contribution of breakup starts increasing at energies below the Coulomb barrier, in contrast to the behavior of other reaction channels, which get closed as energy is lowered. The large probability of projectile breakup at sub-Coulomb energies leads to the observation of a nonzero imaginary potential even at E{sub lab}{<=}0.8V{sub B}.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

In-beam {gamma}-ray spectroscopy of {sup 35}Mg and {sup 33}Na

Excited states in the very neutron-rich nuclei {sup 35}Mg and {sup 33}Na were populated in the fragmentation of a {sup 38}Si projectile beam on a Be target at 83 MeV/u beam energy. We report on the first observation of {gamma}-ray transitions in {sup 35}Mg, the odd-N neighbor of {sup 34}Mg and {sup 36}Mg, which are known to be part of the 'island of inversion' around N=20. The results are discussed in the framework of large-scale shell-model calculations. For the A=3Z nucleus {sup 33}Na, a new {gamma}-ray transition was observed that is suggested to complete the {gamma}-ray cascade 7/2{sup +}{yields}5/2{sup +}{yields}3/2{sub gs}{sup +} connecting three neutron two-particle-two-hole intruder states that are predicted to form a close-to-ideal K=3/2 rotational band in the strong-coupling limit.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

O(6)-symmetry breaking in the {gamma}-soft nucleus {sup 126}Xe and its evolution in the light stable xenon isotopes

Low-lying collective states in {sup 126}Xe have been investigated via the {sup 12}C({sup 126}Xe,{sup 126}Xe{sup *}) projectile Coulomb excitation reaction at 399 MeV. The {gamma} decays were detected with the Gammasphere array. Coulomb excitation cross sections relative to the 2{sub 1}{sup +} state were obtained. Twenty-two absolute E2 transition strengths have been deduced. An sd- interacting boson model (IBM-1) fit agrees well with the new experimental data. This makes a quantitative test of O(6)-symmetry breaking in {sup 126}Xe possible. The measured absolute B(E2) values indicate a preservation of O(5) symmetry, while the O(6) symmetry is broken. The evolution of O(6)-symmetry breaking and of O(5)-symmetry conservation in the {sup 124,126,128}Xe isotopic chain is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Transverse collective flow and midrapidity emission of isotopically identified light charged particles

The transverse flow and relative midrapidity yield of isotopically identified light charged particles (LCPs) has been examined for the 35 MeV/nucleon {sup 70}Zn+{sup 70}Zn, {sup 64}Zn+{sup 64}Zn, and {sup 64}Ni+{sup 64}Ni systems. A large enhancement of the midrapidity yield of the LCPs was observed relative to the yield near the projectile rapidity. In particular, this enhancement was increased for the more neutron-rich LCPs demonstrating a preference for the production of neutron-rich fragments in the midrapidity region. Additionally, the transverse flow of the LCPs was extracted, which provides insight into the average movement of the particles in the midrapidity region. Isotopic and isobaric effects were observed in the transverse flow of the fragments. In both cases, the transverse flow was shown to decrease with an increasing neutron content in the fragments. A clear inverse relationship between the transverse flow and the relative midrapidity yield is shown. The increased relative midrapidity emission produces a decreased transverse flow. The stochastic mean-field model was used for comparison to the experimental data. The results showed that the model was able to reproduce the general isotopic and isobaric trends for the midrapidity emission and transverse flow. The sensitivity of these observables to the density dependence of the symmetry energy was explored. The results indicate that the transverse flow and midrapidity emission of the LCPs are sensitive to the denisty dependence of the symmetry energy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Relativistic description of inclusive quasielastic proton-nucleus scattering with relativistic distorted-wave impulse approximation and random-phase approximation

We present a fully relativistic model for polarized inclusive quasielastic proton-nucleus scattering that includes relativistic distorted waves for the projectile and ejectile (RDWIA), as well as the relativistic random-phase approximation (RPA) applied to the target nucleus. Using a standard relativistic impulse approximation treatment of quasielastic scattering and a two-body Scalar, Pseudoscalar, Vector, Axial vector, Tensor (SPVAT) form of the current operator, it is shown how the behavior of the projectile/ejectile and target can be decoupled. Distortion effects are included via a full partial-wave expansion of the relativistic wave functions. Target correlations are included via the relativistic RPA applied to mean-field theory in quantum hadrodynamics. A number of novel analytical and numerical techniques are employed to aid in this highly nontrivial calculation. A baseline plane-wave calculation is performed for the reaction {sup 40}Ca(p-vector,p-vector{sup '}) at an energy of 500 MeV and an angle {theta}{sub c.m.}=40 deg. Here it is found that the effect of isoscalar correlations is a quenching of the cross section that is expected to become more pronounced at lower energies or for higher-density targets. A RDWIA calculation shows additional reduction and if isoscalar target correlations are included this effect is enhanced.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Relativistic distorted-wave analysis of quasielastic proton-nucleus scattering

A relativistic distorted-wave impulse approximation formalism is presented for the calculation of quasielastic proton-nucleus scattering. It is shown that the double differential cross section may be written as a contraction between the hadronic tensor (describing the projectile and ejectile) and the polarization tensor (describing the nuclear target) and that this mathematical structure also holds for the case where distortions are included. The eikonal approximation is used to introduce distortions in the wave functions, and the nuclear response is described using a Fermi gas model. The highly oscillatory nine-dimensional integrand contained in the expression for the double differential cross section is computed using a novel technique based on combining traditional Gaussian integration methods with the powerful fitting functions in the matlab programming language. This work has successfully calculated the distorted-wave quasielastic differential cross section for proton-nucleus scattering within a fully relativistic framework. It is found that the distortions lead to a reduction in the double differential cross section and have a negligible effect on the computed spin observables.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Production of heavy and superheavy neutron-rich nuclei in transfer reactions

The problem of production and study of heavy neutron-rich nuclei has been intensively discussed during recent years. Many reasons arouse a great interest in this problem. The present limits of the upper part of the nuclear map are very close to the {beta} stability line while the unexplored area of heavy neutron-rich nuclides (also those located along the neutron closed shell N=126 to the right-hand side of the stability line) is extremely important for nuclear astrophysic investigations and, in particular, for the understanding of the r process of astrophysical nucleogenesis. For elements with Z>100 only neutron deficient isotopes (located to the left of the stability line) have been synthesized so far. The 'northeast' area of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes widely used nowadays for the production of new nuclei. Multinucleon transfer processes in near barrier collisions of heavy (and very heavy, U-like) ions seem to be the only reaction mechanism allowing us to produce and explore neutron-rich heavy nuclei including those located at the superheavy island of stability. In this paper several transfer reactions for different projectile-target combinations are studied in detail. Besides the predictions for the cross sections of such processes, we also analyze the angular and energy distributions of primary and survived reaction products in the laboratory frame. These results, as well as predicted excitation functions for the yields of neutron-rich superheavy isotopes, might be useful for the design of appropriate experimental equipment and for carrying out experiments of such kind.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Role of colliding geometry on the balance energy of mass-asymmetric systems

We study the role of colliding geometry on the balance energy (E{sub bal}) of mass-asymmetric systems by varying the mass asymmetry ({eta} =A{sub T}-A{sub p}/A{sub T}+A{sub P}, where A{sub T} and A{sub P} are the masses of the target and projectile, respectively) from 0.1 to 0.7, over the mass range 40-240 and on the mass dependence of the balance energy. Our findings reveal that colliding geometry has a significant effect on the E{sub bal} of asymmetric systems. We find that, as we go from central collisions to peripheral ones, the effect of mass asymmetry on E{sub bal} increases throughout the mass range. Interestingly, we find that for every fixed system mass (A{sub tot}) the effect of the impact parameter variation is almost uniform throughout the mass-asymmetry range. For each {eta}, E{sub bal} follows a power-law behavior ({proportional_to}A{sup {tau}}) at all colliding geometries.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗