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Results for “OXYGEN 18 REACTIONS”

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 OSTI2010

First Experimental Measurement of the {sup 18}O(p,{alpha}){sup 15}N Reaction at Astrophysical Energies

The {sup 18}O(p,{alpha}){sup 15}N and {sup 17}O(p,{alpha}){sup 14}N reactions are of primary importance in several as-trophysical scenarios, including nucleosynthesis inside Asymptotic Giant Branch stars and oxygen and nitrogen isotopic ratios in meteorite grains. They are also key reactions to understand exotic systems such as R-Coronae Borealis stars and novae. Thus, the measurement of their cross sections in the low energy region can be crucial to reduce the nuclear uncertainty on theoretical predictions, because the resonance parameters are poorly determined. The Trojan Horse Method, in its newly developed form particularly suited to investigate low-energy resonances, has been applied to the {sup 2}H({sup 18}O,{alpha}{sup 15}N)n and {sup 2}H({sup 17}O,{alpha}{sup 14}N)n reactions to deduce the {sup 18}O(p,{alpha}){sup 15}N and {sup 17}O(p,{alpha}){sup 14}N cross sections at low energies. Resonances in the {sup 18}O(p,{alpha}){sup 15}N and {sup 17}O(p,{alpha}){sup 14}N excitation functions have been studied and the resonance parameters deduced.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Comparison of the {sup 7}Li({sup 18}O,{sup 17}N){sup 8}Be and {sup 18}O(d,{sup 3}He){sup 17}N reactions

New angular distributions for the {sup 7}Li({sup 18}O,{sup 17}N){sup 8}Be reaction at an energy of E{sub lab}({sup 18}O)=114 MeV for the ground states of {sup 8}Be and {sup 17}N and the excited states of {sup 17}N were measured. These data and {sup 18}O(d,{sup 3}He){sup 17}N reaction data taken at E{sub d}=52 MeV were analyzed within the coupled-reaction-channels method using {sup 7}Li+{sup 18}O and {sup 18}O + d optical potentials deduced from previous elastic and inelastic scattering results. Shell-model spectroscopic amplitudes were used in the analysis. Both reactions are dominated by single proton transfer. Calculations show that heavy-ion reactions of the type studied in this work can be used to identify final-state spins when measurements are carried to small angles.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Possible chiral bands in {sup 194}Tl

High spin states in {sup 194}Tl, excited through the {sup 181}Ta({sup 18}O,5n) fusion evaporation reaction, were studied using the AFRODITE array at iThemba LABS. Candidate chiral bands built on the {pi}h{sub 9/2} x {nu}i{sub 13/2}{sup 1} configuration were found. Furthermore these bands were observed through a band crossing caused by the excitation of a {nu}i{sub 13/2} pair. Above the band crossing the excitation energies remain close, suggesting that chirality may persist for the four quasiparticle configuration too.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Dynamical model of surrogate reactions

A new dynamical model is developed to describe the whole process of surrogate reactions: Transfer of several nucleons at an initial stage, thermal equilibration of residues leading to washing out of shell effects, and decay of populated compound nuclei are treated in a unified framework. Multidimensional Langevin equations are employed to describe time evolution of collective coordinates with a time-dependent potential energy surface corresponding to different stages of surrogate reactions. The new model is capable of calculating spin distributions of the compound nuclei, one of the most important quantities in the surrogate technique. Furthermore, various observables of surrogate reactions can be calculated, for example, energy and angular distribution of ejectile and mass distributions of fission fragments. These features are important to assess validity of the proposed model itself, to understand mechanisms of the surrogate reactions, and to determine unknown parameters of the model. It is found that spin distributions of compound nuclei produced in {sup 18}O+{sup 238}U{yields}{sup 16}O+{sup 240}*U and {sup 18}O+{sup 236}U{yields}{sup 16}O+{sup 238}*U reactions are equivalent and much less than 10({h_bar}/2{pi}) and therefore satisfy conditions proposed by Chiba and Iwamoto [Phys. Rev. C 81, 044604 (2010)] if they are used as a pair in the surrogate ratio method.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Quantum description of coupling to neutron-rearrangement channels in fusion reactions near the Coulomb barrier

The fusion cross sections for the {sup 17,18}O+{sup 27}Al, {sup 18}O+{sup 58}Ni, and {sup 6}He+{sup 197}Au reactions were calculated by the coupled-channel method. The radial dependence of matrices that describe coupling to valence-neutron-rearrangement channels was determined with the aid of two-center wave functions. The coupling-strength parameters were evaluated on the basis of numerically solving the time-dependent Schrödinger equation. Satisfactory agreement with experimental data was obtained.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Near-barrier quasielastic scattering as a sensitive tool to derive nuclear matter diffuseness

Quasielastic excitation functions for the {sup 16,18}O + {sup 60}Ni systems were measured at energies near and below the Coulomb barrier, at the backward angle {theta}{sub LAB} = 161 deg. The corresponding quasielastic barrier distributions were derived. The data were compared with predictions from coupled channel calculations using a double-folding potential as a bare potential. For the {sup 16}O-induced scattering, good agreement was obtained for the barrier distribution by using the projectile default nuclear matter diffuseness obtained from the Sao Paulo potential systematic, that is, 0.56 fm. However, for the {sup 18}O-induced scattering, good agreement was obtained only when the projectile nuclear matter diffuseness was changed to 0.62 fm. Therefore, in this paper we show how near-barrier quasielastic scattering can be used as a sensitive tool to derive nuclear matter diffuseness.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Multipolarity analysis for {sup 14}C high-energy resonance populated by ({sup 18}O,{sup 16}O) two-neutron transfer reaction

The {sup 12}C({sup 18}O,{sup 16}O){sup 14}C reaction at 84 MeV incident energy has been explored up to high excitation energy of the residual nucleus thanks to the use of the MAGNEX spectrometer to detect the ejectiles. In the region above the two-neutron separation energy, a resonance has been observed at 16.9 MeV. A multipolarity analysis of the cross section angular distribution indicates an L = 0 character for such a transition.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

The ({sup 18}O, {sup 16}O) reaction as a probe for nuclear spectroscopy

The response of nuclei to the ({sup 18}O, {sup 16}O) two-neutron transfer reaction at 84 MeV incident energy has been systematically studied at the Catania INFN-LNS laboratory. The experiments were performed using several solid targets from light ({sup 9}Be, {sup 11}B, {sup 12,13}C, {sup 16}O, {sup 28}Si) to heavy ones ({sup 58,64}Ni, {sup 120}Sn, {sup 208}Pb). The {sup 16}O ejectiles were detected at forward angles by the MAGNEX magnetic spectrometer. Exploiting the large momentum acceptance (−10%, +14%) and solid angle (50 msr) of the spectrometer, energy spectra were obtained with a relevant yield up to about 20 MeV excitation energy. The application of the powerful trajectory reconstruction technique did allow to get energy spectra with energy resolution of about 150 keV and angular distributions with angular resolution better than 0.3°. A common feature observed with light nuclei is the appearance of unknown resonant structures at high excitation energy. The strong population of these latter together with the measured width can reveal the excitation of a collective mode connected with the transfer of a pair.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Peripheral elastic and inelastic scattering of {sup 17,18}O on light targets at 12 MeV/nucleon

The elastic and inelastic scattering of {sup 17,18}O with light targets has been undertaken at 12 MeV/nucleon in order to determine the optical potentials needed for the transfer reaction {sup 13}C({sup 17}O,{sup 18}O){sup 12}C. Optical potentials in both incoming and outgoing channels have been determined in a single experiment. This transfer reaction was used to infer the direct capture rate to the {sup 17}F(p,γ){sup 18}Ne which is essential to estimate the production of {sup 18}F at stellar energies in ONe novae. We demonstrate the stability of the ANC method and OMP results using good quality elastic and inelastic scattering data with stable beams. The peripherality of our reaction is inferred from a semiclassical decomposition of the total scattering amplitude into barrier and internal barrier components. Comparison between elastic scattering of {sup 17}O, {sup 18}O and {sup 16}O projectiles is made.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Production and decay properties of the 1.9-s isomeric state in {sup 261}Rf

The 1.9-s isomeric state ({sup 261}Rf{sup b}) in {sup 261}Rf was directly populated in the {sup 248}Cm({sup 18}O,5n){sup 261}Rf{sup b} reaction. Alpha and spontaneous fission (SF) decays of {sup 261}Rf{sup b}, as well as the 68-s state {sup 261}Rf{sup a}, was investigated with a rotating wheel apparatus under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. An identification of {sup 261}Rf{sup b} was based on {alpha}-{alpha} correlations linking {alpha} decays of {sup 261}Rf{sup b} and its daughter {sup 257}No. The {alpha}-particle energy of {sup 261}Rf{sup b} was measured to be 8.52 {+-} 0.05 MeV. The half-life was determined to be 1.9 {+-} 0.4 s based on both 8.52-MeV {alpha} and SF decays. The {alpha} and SF branches are 0.27 {+-} 0.06 and 0.73 {+-} 0.06, respectively. The cross section for the {sup 248}Cm({sup 18}O,5n){sup 261}Rf{sup b} reaction is {sigma}({sup 261}Rf{sup b}) = 11 {+-} 2 nb at 95.1 MeV, which gives a cross-section ratio of {sigma}({sup 261}Rf{sup a})/{sigma}({sup 261}Rf{sup b}) = 1.1 {+-} 0.2.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Allowance for the shell structure of colliding nuclei in the fusion-fission process

The motion of two nuclei toward each other in fusion-fission reactions is considered. The state of the system of interacting nuclei is specified in terms of three collective coordinates (parameters). These are the distance between the centers of mass of the nuclei and the deformation parameter for each of them (the nose-to-nose orientation of the nuclei is assumed). The evolution of collective degrees of freedom of the system is described by Langevin equations. The energies of the Coulomb and nuclear (Gross-Kalinovsky potential) interactions of nuclei are taken into account in the potential energy of the system along with the deformation energy of each nucleus with allowance for shell effects. The motion of nuclei toward each other are calculated for two reaction types: reactions involving nuclei that are deformed ({sub 42}{sup 100}Mo + {sub 42}{sup 100}Mo {yields} {sub 84}{sup 200}Po) and those that are spherical ({sub 82}{sup 208}Pb + {sub 8}{sup 18}O {yields} {sub 90}{sup 226}Th) in the ground state. It is shown that the shell structure of interacting nuclei affects not only the fusion process as a whole (fusionbarrier height and initial-reaction-energy dependence of the probability that the nuclei involved touch each other) but also the processes occurring in each nucleus individually (shape of the nuclei and their excitation energies at the point of touching).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

First observation of high-spin states in {sup 214}Po: Probing the valence space beyond {sup 208}Pb

Excited states in {sup 214}Po have been populated using the {sup 18}O + {sup 208}Pb reaction at 85-MeV beam energy and studied with the Euroball IV {gamma}-multidetector array. The level scheme has been built up to {approx}2.7-MeV excitation energy and spin I=12({h_bar}/2{pi}) from the triple-{gamma} coincidence data. Spin and parity values of most of the observed states have been assigned from the {gamma}-angular properties. The configurations of the yrast states are discussed using results of empirical shell-model calculations and by analogy with the neighboring nuclei. The {sup 214}Po level scheme established in this work constitutes an important step for the determination of the effective nucleon-nucleon interactions beyond N=126.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

High-spin states in the five-valence-particle nucleus {sup 213}Po

Excited states in {sup 213}Po have been populated using the {sup 18}O+ {sup 208}Pb reaction at 85 MeV beam energy and studied with the Euroball IV {gamma} multidetector array. The level scheme has been built up to {approx}2.0 MeV excitation energy and spin I{approx}25/2({h_bar}/2{pi}) from the triple {gamma} coincidence data. Spin and parity values of several yrast states have been assigned from the {gamma} angular properties. The configurations of the yrast states are discussed using results of empirical shell-model calculations and by analogy with the neighboring nuclei. The spin and parity values of several low-spin states of {sup 213}Po previously identified from the {beta} decay of {sup 213}Bi are revised.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Nuclear Data Sheets for A = 30

Evaluated spectroscopic data and level schemes from radioactive decay and nuclear reaction studies are presented for {sup 30}F, {sup 30}Ne, {sup 30}Na, {sup 30}Mg, {sup 30}Al, {sup 30}Si, {sup 30}P, {sup 30}S, and {sup 30}Cl. This evaluation for A=30 supersedes the previous evaluation 1998En04. However, some additional information for these nuclides can be found in earlier evaluations 1990En08 and 1978En02. Highlights of this publication are the following: The latest studies (2010StZZ, 2010De26) by fusion evaporation reaction of {sup 14}C and {sup 18}O using GAMMASPHERE array, consisted of 101 Compton-suppressed HPGe detectors, provided new data for {sup 30}Al, {sup 30}Si, and {sup 30}Mg nuclides and extended the level scheme to higher spin states. 2010Se07 reported a new level at 4814(3) keV for {sup 30}S nuclide studied by the {sup 32}S(p,t) reaction. It did not observe the 5168(6) keV level that was reported earlier as a possible doublet by 2007Ba69. In the absence of further experiment, 2010Se07 considers the level as one of the doublets.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

({sup 18}O,{sup 18}Ne) double charge-exchange with MAGNEX

An experimental study concerning Double Gamow-Teller (DGT) modes in ({sup 18}O,{sup 18}Ne) Double Charge-Exchange reactions has been very recently performed at INFN-LNS laboratory in Catania. The experiment was performed using a {sup 40}Ca solid target and a {sup 18}O Cyclotron beam at 270 MeV incident energy. Charged ejectiles produced in the reaction were momentum analyzed and identified by MAGNEX spectrometer at very forward angles. Preliminary results are presented in the present paper.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Two-neutron stripping in ({sup 18}O, {sup 16}O) and (t,p) reactions

The {sup 12}C({sup 18}O,{sup 16}O){sup 14}C reactions has been investigated at 84 MeV incident energy. The charged ejectiles produced in the reaction have been momentum analyzed and identified by the MAGNEX magnetic spectrometer. Q-value spectra have been extracted with an energy resolution of 160 keV (Full Width at Half Maximum) and several known bound and resonant states of {sup 14}C have been identified up to 15 MeV. In particular, excited states with dominant 2p - 4h configuration are the most populated. The absolute values of the cross sections have been extracted showing a striking similarity with those measured for the same transitions by (t,p) reactions. This indicates that the effect of the {sup 16}O core is negligible in the reaction mechanism.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

THE RGB AND AGB STAR NUCLEOSYNTHESIS IN LIGHT OF THE RECENT {sup 17}O(p, {alpha}){sup 14}N AND {sup 18}O(p, {alpha}){sup 15}N REACTION-RATE DETERMINATIONS

In recent years, the Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of proton-induced reactions on A = 17 and A = 18 oxygen isotopes, overcoming extrapolation procedures and enhancement effects due to electron screening. In particular, the strengths of the 20 keV and 65 keV resonances in the {sup 18}O(p, {alpha}){sup 15}N and {sup 17}O(p, {alpha}){sup 14}N reactions, respectively, have been extracted, as well as the contribution of the tail of the broad 656 keV resonance in the {sup 18}O(p, {alpha}){sup 15}N reaction inside the Gamow window. The strength of the 65 keV resonance in the {sup 17}O(p, {alpha}){sup 14}N reaction, measured by means of the THM, has been used to renormalize the corresponding resonance strength in the {sup 17}O + p radiative capture channel. As a result, more accurate reaction rates for the {sup 18}O(p, {alpha}){sup 15}N, {sup 17}O(p, {alpha}){sup 14}N, and {sup 17}O(p, {gamma}){sup 18}F processes have been deduced, devoid of systematic errors due to extrapolation or the electron screening effect. Such rates have been introduced into state-of-the-art red giant branch and asymptotic giant branch (AGB) models for proton-capture nucleosynthesis coupled with extra-mixing episodes. The predicted abundances have been compared with isotopic compositions provided by geochemical analysis of presolar grains. As a result, an improved agreement is found between the models and the isotopic mix of oxide grains of AGB origins, whose composition is the signature of low-temperature proton-capture nucleosynthesis. The low {sup 14}N/{sup 15}N found in SiC grains cannot be explained by the revised nuclear reaction rates and remains a serious problem that has not been satisfactorily addressed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Radioactive ion beam transportation for the fundamental symmetry study with laser-trapped atoms

The search for the violation of the fundamental symmetry in a radioactive atom is the promising candidate for precision tests of the standard model and its possible extensions. The subtle signal arising from the symmetry violation is enhanced in heavy atoms, such as a francium (Fr). To realize high precision measurements, a large amount of radioactive isotopes is required. The Fr is produced via a nuclear fusion reaction using a melted gold target with a {sup 18}O primary beam at Cyclotron and Radioisotope Center, Tohoku University. The maximum extraction efficiency of the Fr ion was achieved at approximately 35%. The beam line consists of an electrostatic deflector, three electrostatic quadrupole triplets to the measurement area at 10 m away from the reaction point, and several beam diagnosis systems. We optimized parameters of the beam line.

43 PARTICLE ACCELERATORS↗