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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 OSTI2010

Discovery of Highly Excited Long-Lived Isomers in Neutron-Rich Hafnium and Tantalum Isotopes through Direct Mass Measurements

A study of cooled {sup 197}Au projectile-fragmentation products has been performed with a storage ring. This has enabled metastable nuclear excitations with energies up to 3 MeV, and half-lives extending to minutes or longer, to be identified in the neutron-rich nuclides {sup 183,184,186}Hf and {sup 186,187}Ta. The results support the prediction of a strongly favored isomer region near neutron number 116.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Nuclear Data Sheets for A=182

Nuclear spectroscopic information for known nuclides of mass number 182 (Lu,Hf,Ta,W,Re,Os,Ir,Pt,Au,Hg, Tl,Pb) with Z=71 to 82 and N=111 to 100 have been evaluated and presented together with adopted energies and J{pi} of levels in these nuclei. No excited state data are yet available for {sup 182}Lu, while only limited structure information is available for {sup 182}Pb and {sup 182}Tl. Rotational band structures are known for {sup 182}Hg and {sup 182}Au but spin-parity assignments remain largely tentative. The decays of {sup 182}Lu, {sup 182}Hg, {sup 182}Au and {sup 182}Tl are not well established. The {sup 182}Hf isotope is of geophysical and astrophysical interest. This evaluation supersedes previous full evaluations of A=182 published by 1988Fi05 and 1975Sc13, and a selected (mainly high-spin) update of A=182 published by 1995Si04.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Multi-quasiparticle structures up to spin {approx}44({h_bar}/2{pi}) in the odd-odd nucleus {sup 168}Ta

High-spin states in the odd-odd nucleus {sup 168}Ta have been populated in the {sup 120}Sn({sup 51}V,3n) reaction. Two multi-quasiparticle structures have been extended significantly from spin {approx}20({h_bar}/2{pi}) to above 40({h_bar}/2{pi}). As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly coupled rotational bands are proposed based on signature splitting, B(M1)/B(E2) ratio information, and observed rotation-alignment behavior. Properties of the observed bands in {sup 168}Ta are compared to related structures in the neighboring odd-Z, odd-N, and odd-odd nuclei and are discussed within the framework of the cranked shell model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Neutrino reactions on {sup 138}La and {sup 180}Ta via charged and neutral currents by the quasiparticle random-phase approximation

The cosmological origins of the two heaviest odd-odd nuclei {sup 138}La and {sup 180}Ta are believed to be closely related to the neutrino process. We investigate in detail neutrino-induced reactions on the nuclei. Charged current (CC) reactions {sup 138}Ba({nu}{sub e},e{sup -}){sup 138}La and {sup 180}Hf({nu}{sub e},e{sup -}){sup 180}Ta are calculated using the standard quasi-particle random phase approximation (QRPA) with neutron-proton pairing as well as neutron-neutron and proton-proton pairing correlations. For the neutral current (NC) reactions {sup 139}La({nu},{nu}{sup '}){sup 139}La{sup *} and {sup 181}Ta({nu},{nu}{sup '}){sup 181}Ta{sup *}, we generate ground and excited states of the odd-even target nuclei {sup 139}La and {sup 181}Ta by operating one quasiparticle to even-even nuclei {sup 138}Ba and {sup 180}Hf, which are assumed as the BCS ground state. Numerical results for CC reactions are shown to be consistent with recent semiempirical data deduced from the Gamow-Teller strength distributions measured in the ({sup 3}He,t) reaction. Results for NC reactions are estimated to be about 4 to 5 times smaller than the results for CC reactions. Finally, cross sections weighted by the incident neutrino flux in the core-collapse supernova are presented for further applications to the network calculations for relevant nuclear abundances.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Band crossings in {sup 166}Ta

High-spin states in the odd-odd nucleus {sup 166}Ta are investigated through the 5n channel of the {sup 51}V+{sup 120}Sn reaction. Four new bands are observed and linked into the previous level scheme. Configurations for the bands are proposed, based on measured alignments and B(M1)/B(E2) transition strength ratios.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Precision measurements of proton emission from the ground states of {sup 156}Ta and {sup 160}Re

The decays of the {pi}d{sub 3/2} ground states of {sup 156}Ta and {sup 160}Re have been studied in detail using the GREAT spectrometer. More than 7000 {sup 160}Re nuclei were produced in reactions of 290- and 300-MeV {sup 58}Ni ions with an isotopically enriched {sup 106}Cd target and separated in flight using the RITU separator. The proton and {alpha} decays of the {pi}d{sub 3/2} level were confirmed and the half-life and branching ratios of this state were determined with improved precision to be t{sub 1/2}=611{+-}7 {mu}s and b{sub p}=89{+-}1% and b{sub {alpha}=}11{+-}1%, respectively. The {alpha}-decay branch populated the ground state of {sup 156}Ta, allowing improved values for the proton-decay energy and half-life to be obtained (E{sub p}=1011{+-}5 keV; t{sub 1/2}=106{+-}4 ms). The {beta} decay of this level was identified for the first time and a branching ratio of b{sub {beta}=}29{+-}3% was deduced. The spectroscopic factors deduced from these measurements are compared with predictions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Possibility of implementing a nondirect experiment aimed at determining the cross section for nucleon interaction with an excited nucleus

With the aid of experimental data on the level densities in the even-odd tungsten isotopes {sup 183,185,187}W as determined in the respective (n, 2{rho}) reactions, the ratio of the cross section for the interaction of an excited nucleus with a neutron to its counterpart calculated on the basis of the optical model of the nucleus was obtained from the spectra of evaporated neutrons in the reaction {sup 181}Ta(p, n){sup 181}W. A significant local increase in this ratio is qualitatively interpreted as that which is due to the possible increase in the penetrability of the nuclear surface for nucleon reaction products because of the effect of phonon-type excitations. Sources of possible nonstandard systematic errors in experimentally determining the level density in an arbitrary nucleus at energies below the nucleon binding energy B{sub n} are analyzed. The extraction of information from the distribution of the intensities of cascades belonging to the nucleon and photon type is simulated. The resulting information may be highly reliable if use is made of the entire body of experimental data on the nucleus under analysis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Calculation of proton total reaction cross sections for some target nuclei in incident energy range of 10-600 MeV

In this study, proton total reaction cross sections have been investigated for some isotopes such as {sup 12}C, {sup 27}Al, {sup 9}Be, {sup 16}O, {sup 181}Ta, {sup 197}Au, {sup 6}Li, and {sup 14}N by a proton beam up to 600 MeV. Calculation of the proton total cross sections has been carried out by the analytic expression formulated by M.A. Alvi by using Coulomb-modified Glauber theory with the Helm model nuclear form factor. The obtained results have been discussed and compared with the available experimental data and found to be in agreement with each other.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Discovery of tantalum, rhenium, osmium, and iridium isotopes

Currently, thirty-eight tantalum, thirty-eight rhenium, thirty-nine osmium, and thirty-eight iridium isotopes have been observed and the discovery of these isotopes is described here. For each isotope a brief synopsis of the first refereed publication, including the production and identification method, is presented.

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

Influence of dynamical parameters on pre-scission particles and fission probability in heavy-ion collisions

A stochastic approach to fission dynamics based on one- and three-dimensional Langevin equations was applied to calculate the fission probability and the pre-scission particle multiplicity. Evaporation of pre-scission light particles along Langevin fission trajectories from the ground state of the compound nucleus to its scission and fission probability have been calculated using a Monte Carlo simulation technique. To examine this approach we used {sup 19}F+{sup 181}Ta and {sup 16}O+{sup 197}Au systems. Our results show that the fission probability and pre-scission particle multiplicity in three dimensions is different from the one-dimensional Langevin approach. The theoretical results of pre-scission neutron, proton, and {alpha}-particle multiplicities and the fission probability for given systems based on this model are compared with available experimental data. The obtained results using three-dimensional calculations are in better agreement with experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Identification of fission-like events in the {sup 16}O + {sup 181}Ta system: Mass and isotopic yield distribution

In this paper, nuclear reaction cross sections for 24 fission-like fragments (30{<=}Z{<=}60) have been measured for the 6.5 MeV/A {sup 16}O + {sup 181}Ta system. The recoil-catcher activation technique was employed followed by off-line {gamma} spectroscopy. The isotopic yield distributions for yttrium and indium isotopes have been obtained from the experimental data. The variance of the presently measured isotopic yield distributions have been found to be in agreement with the literature values. However, the variance of the mass distribution of fission residues has found to be narrower as compared to other relatively heavier systems. A self-consistent approach to determining the isobaric charge dispersion parameters has been adopted. The measured fission cross sections at 97 and 100 MeV are satisfactorily described by a statistical model code. An attempt has been made to explain the production cross sections of intermediate mass residues in the fission of heavy residues populated via complete and/or incomplete fusion processes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Nucleosynthesis and Neutrinos

Neutrinos play the critical roles in nucleosynthesis of light-to-heavy mass nuclei in core-collapse supernovae. We study the nucleosynthesis induced by neutrino interactions and find suitable average neutrino temperatures in order to explain the observed solar system abundances of several isotopes {sup 7}Li, {sup 11}B, {sup 138}La and {sup 180}Ta. These isotopes are predominantly synthesized by the supernova {nu}-process. We also study the neutrino oscillation effects on their abundances and propose a method to determine the unknown neutrino oscillation parameters, i.e. {theta}{sub 13} and mass hierarchy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

{sup 11}B and Constraints on Neutrino Oscillations and Spectra from Neutrino Nucleosynthesis

We study the sensitivity to variations in the triple-alpha and {sup 12}C({alpha},{gamma}){sup 16}O reaction rates, of the yield of the neutrino-process isotopes {sup 7}Li, {sup 11}B, {sup 19}F, {sup 138}La, and {sup 180}Ta in core-collapse supernovae. Compared to solar abundances, less than 15% of {sup 7}Li, about 25%-80% of {sup 19}F, and about half of {sup 138}La is produced in these stars. Over a range of {+-}2{sigma} for each helium-burning rate, {sup 11}B is overproduced and the yield varies by an amount larger than the variation caused by the effects of neutrino oscillations. The total {sup 11}B yield, however, may eventually provide constraints on supernova neutrino spectra.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Photo-nuclear astrophysics in NewSUBARU {gamma}-ray source

A laser Compton scattering (LCS){gamma}-ray source has been installed at an electron storage ring NewSUBARU at SPring-8. We have studied the nuclear physics using this LCS g-ray source. The half-lives of unstable isotopes, {sup 184}Re and {sup 164}Ho{sup m}, produced by photo-induced reactions have been measured. These half-lives are shorter than previous recommended values by 7% and 3%, respectively. These changes of the half-lives affects to evaluation of cross-sections using the activation method. We have discussed a problem of the residual ratio of an isomer in {sup 180}Ta in supernova explosions. The unstable ground state and the metastable isomer are linked by ({gamma}, {gamma}') reactions. We have developed a new time-dependent model to calculate the isomer ratio in supernovae. The solar abundance of {sup 180}Ta is reproduced by the supernova neutrino process with the present calculated isomer ratio.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

On the question of connections between high-K and low-K states in {sup 180}Ta and {sup 176}Lu

Possible connections between the high- and low-K states in the odd-odd isotopes {sup 176}Lu and {sup 180}Ta are discussed in the context of photoactivation resonances, and the implications for excitations in a stellar environment. Recent spectroscopic studies using (d, 2n) reactions provide limits on the {gamma}-ray branches expected if proposed intermediate states are correct in {sup 180}Ta and {sup 176}Lu, while Deep-inelastic measurements have observed a definitive set of connections in {sup 176}Lu.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Rotational structures and the wobbling mode in {sup 167}Ta

Excited states in the neutron-deficient nucleus {sup 167}Ta were studied through the {sup 120}Sn({sup 51}V,4n) reaction. Twelve rotational bands have been observed and the relative excitation energy of each sequence is now known owing to the multiple interband connections. Several quasineutron alignments were observed that aided in the quasiparticle assignments of these bands. The resulting interpretation is in line with observations in neighboring nuclei. Trends in the wobbling phonon energy seen in {sup 161,163,165,167}Lu and {sup 167}Ta are also discussed and particle-rotor model calculations (assuming constant moments of inertia) are found to be inconsistent with the experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Reanalysis of the (J=5) state at 592 keV in {sup 180}Ta and its role in the {nu}-process nucleosynthesis of {sup 180}Ta in supernovae

We analyze the production and freeze-out of the isomer {sup 180}Ta{sup m} in the {nu}-process. We consider the influence of a possible low-lying intermediate (J=5) state at 592 keV using a transition width estimated from the measured half-life. This more realistic width is much smaller than the previous estimate. We find that the 592-keV state leads only to a small reduction of the residual isomer population ratio from the previous result; that is, considering this better estimate for the transition width, the isomer population ratio changes from R=0.39 to R=0.38, whereas previously it was estimated that this transition could reduce the ratio to R=0.18. This finding strengthens the evidence that {sup 138}La and {sup 180}Ta are coproduced by neutrino nucleosynthesis with an electron neutrino temperature of kT{approx_equal}4 MeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗