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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Intensity-resolved ionization yields of aniline with femtosecond laser pulses

We present experimental results for the ionization of aniline and benzene molecules subjected to intense ultrashort laser pulses. Measured parent molecular ions yields were obtained using a recently developed technique capable of three-dimensional imaging of ion distributions within the focus of a laser beam. By selecting ions originating from the central region of the focus, where the spatial intensity distribution is nearly uniform, volumetric-free intensity-dependent ionization yields were obtained. The measured data revealed a previously unseen resonance-enhanced multiphoton ionization (REMPI)-like process. Comparison of benzene, aniline, and Xe ion yields demonstrates that the observed intensity-dependent structures are not due to geometric artifacts in the focus. Finally for intensities greater than {approx}3x10{sup 13} W/cm{sup 2}, we attribute the ionization of aniline to a stepwise process going through the {pi}{sigma}{sup *} state which sits three photons above the ground state and two photons below the continuum.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Role of Lithium Codoping in Enhancing the Scintillation Yield of Aluminate Garnets

The aim of this work is to clarify the scintillation-yield enhancement in Lu YAG : Pr scintillators obtained by Li codoping via integrated study of the valence state of activators, the preferential site occupancy of Li codopants, and defect structures from experimental and theoretical insights. Here, with Li codoping, the light yield and energy resolution of 10 × 10 × 10 mm 3 Lu YAG : Pr samples are improved from 156000 to 248000 photons/MeV, and 5.3 to 4.3% at 662 keV,respectively.The optical absorption spectra indicate that Li codoping does not induce conversion of stable Pr 3 + to Pr 4 + in Lu YAG : Pr single crystals. Based on the formation energies of substitutional and interstitial Li sites using density-functional-theory (DFT) calculations and the 7 Li nuclear magnetic resonance results, it is shown that the Li ions prefer to dominantly occupy the fourfold coordinated interstitial sites and fourfold coordinated Al sites. The systematic analysis of thermoluminescence glow curves, positron annihilation lifetime spectroscopies, and defect formation energies derived from DFT calculations reveals that the concentration of isolated Lu and Al vacancies as dominant acceptor defects is reduced by Li codoping, whilst the shallow Li i interstitial defects and the deep V O oxygen vacancies are introduced simultaneously. We propose that the lowering of hole trapping at defects resulting from Li codoping contributes to the scintillation-yield enhancement.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Theoretical description of fission yields: Toward a fast and efficient global model

A recently proposed approach to global modeling of fission fragment distributions is extended to account for odd-even staggering in charge yields and for neutron evaporation. We show that the proposed hybrid model can reproduce experimental mass and charge fragment yields, including the odd-even staggering for a wide range of fissioning nuclei. Experimental isotopic yields can be described within a simple neutron evaporation scheme. Here, we also explore fission fragment distributions of exotic neutron-rich and superheavy systems and compare our predictions with other state-of-the art global calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Fission product yields from the 238 U ( n,f ) reaction at E n = 4.6 MeV

Here, we present cumulative fission product yields from the 238 U (n, f) reaction at an incident energy of 4.6 MeV for fission products with half-lives from less than one second to several hours. We employed direct γ-ray spectroscopy to measure unseparated fission products with a conventional neutron activation analysis and a cyclic activation technique using the RApid Belt-driven Irradiated Target Transfer System (RABITTS). Yields were determined for 78 isotopes and isomers, covering the mass range 84 ≤ A ≤ 148 and the charge range from 33(As) ≤ Z ≤ 58(Ce). Our experimental cumulative yields are compared to the literature and evaluated data at E n ≈0.5 MeV from ENDF/B-VIII.0 and JEFF-3.3 libraries and with theoretical models using the GEF and FREYA codes at E n =4.6 MeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Low-energy {omega} ({yields}{pi}{sup 0}{gamma}) meson photoproduction in the nucleus

The {pi}{sup 0{gamma}} invariant mass distribution spectra in the ({gamma},{pi}{sup 0{gamma}}) reaction were measured by the TAPS/ELSA Collaboration to look for the hadron parameters of the {omega} meson in the Nb nucleus. We study the mechanism for this reaction, where we consider that the elementary reaction in the Nb nucleus proceeds as {gamma}N{yields}{omega}N;{omega}{yields}{pi}{sup 0}{gamma}. The {omega}-meson photoproduction amplitude for this reaction is extracted from the measured four-momentum transfer distribution in the {gamma}p{yields}{omega}p reaction. The propagation of the {omega} meson and the distorted wave function for the {pi}{sup 0} meson in the final state are described by the eikonal form. The {omega} and {pi}{sup 0} mesons' nucleus optical potentials, appearing in the {omega} meson propagator and {pi}{sup 0} meson distorted wave function respectively, are estimated using the t{rho} approximation. The effects of pair correlation and color transparency are also studied. The calculated results do not show medium modification for the {omega} meson produced in the nucleus for momentum greater than 200 MeV. It occurs because the {omega} meson predominantly decays outside the nucleus. The dependence of the cross section on the final-state interaction is also investigated. The broadening of the {omega}-meson mass distribution spectra is shown to occur due to the large resolution width associated with the detector used in the experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Isobaric yield ratios in heavy-ion reactions, and symmetry energy of neutron-rich nuclei at intermediate energies

The isobaric yield ratios of the fragments produced in the neutron-rich {sup 48}Ca and {sup 64}Ni projectile fragmentation are analyzed in the framework of a modified Fisher model. The correlations between the isobaric yield ratios (R) and the energy coefficients in the Weiszaecker-Beth semiclassical mass formula (the symmetry-energy term a{sub sym}, the Coulomb-energy term a{sub c}, and the pairing-energy term a{sub p}) and the difference between the chemical potentials of the neutron and proton ({mu}{sub n}-{mu}{sub p}) are investigated. Simple correlations between ({mu}{sub n}-{mu}{sub p})/T, a{sub c}/T, a{sub sym}/T, and a{sub p}/T (where T is the temperature), and lnR are obtained. It is suggested that ({mu}{sub n}-{mu}{sub p})/T, a{sub c}/T, a{sub sym}/T, and a{sub p}/T of neutron-rich nuclei can be extracted using isobaric yield ratios for heavy-ion collisions at intermediate energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Exploratory study of fission product yields of neutron-induced fission of U 235 , U 238 , and Pu 239 at 8.9 MeV

Using dual-fission chambers each loaded with a thick (200–400–mg/cm 2 ) actinide target of 235,238 U or 239 Pu and two thin (~10–100–μg/cm 2 ) reference foils of the same actinide, the cumulative yields of fission products ranging from 92 Sr to 147 Nd have been measured at E n = 8.9MeV. The 2 H(d,n) 3 He reaction provided the quasimonoenergetic neutron beam. Here, the experimental setup and methods used to determine the fission product yield (FPY) are described, and results for typically eight high-yield fission products are presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Scintillation yield from electronic and nuclear recoils in superfluid He 4

Superfluid $^4$He is a promising target material for direct detection of light ($<$ 1 GeV) dark matter. Possible signal channels available for readout in this medium include prompt photons, triplet excimers, and roton and phonon quasiparticles. The relative yield of these signals has implications for the sensitivity and discrimination power of a superfluid $^4$He dark matter detector. Using a 16~cm$^3$ volume of 1.75~K superfluid $^4$He read out by six immersed photomultiplier tubes, we measured the scintillation from electronic recoils ranging between 36.3 and 185~keV$_\mathrm{ee}$, yielding a mean signal size of $1.25^{+0.03}_{-0.03}$~phe/keV$_\mathrm{ee}$, and nuclear recoils from 53.2 to 1090~keV$_\mathrm{nr}$. We compare the results of our relative scintillation yield measurements to an existing semiempirical model based on helium-helium and electron-helium interaction cross sections. As a result, we also study the behavior of delayed scintillation components as a function of recoil type and energy, a further avenue for signal discrimination in superfluid $^4$He.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nonresonant explanation for the Y(4260) structure observed in the e{sup +}e{sup -}{yields}J/{psi}{pi}{sup +}{pi}{sup -} process

In this work, we propose a nonresonant explanation for the Y(4260) structure observed in the e{sup +}e{sup -}{yields}J/{psi}{pi}{sup +}{pi}{sup -} process, i.e., Y(4260) is not a genuine resonance. Our result indicates that the Y(4260) structure can be reproduced by the interference of production amplitudes of the e{sup +}e{sup -}{yields}J/{psi}{pi}{sup +}{pi}{sup -} processes via direct e{sup +}e{sup -} annihilation and through intermediate charmonia {psi}(4160)/{psi}(4415). Besides describing the Y(4260) line shape in e{sup +}e{sup -}{yields}J/{psi}{pi}{sup +}{pi}{sup -} well, such a nonresonant explanation for the Y(4260) structure naturally answers why there is no evidence of Y(4260) in the exclusive open-charm decay channel and R-value scan.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Do new data on B{sup +{yields}{tau}+{nu}}{sub {tau}} decays point to an early discovery of supersymmetry at the LHC?

The recent Belle and BABAR measurements of the branching ratio of B{sup +{yields}{tau}+{nu}}{sub {tau}} indicate a significant deviation from the standard model prediction. We demonstrate that this measurement has a serious impact on models with minimal flavor violation involving a charged Higgs boson, ruling out a large portion of the currently allowed parameter space. In the constrained minimal supersymmetric standard model, this creates a tension between the measurements of B{sup +{yields}{tau}+{nu}}{sub {tau}} and the anomalous magnetic moment of the muon, unless tan{beta} is small, {mu}>0, and A{sub 0} takes a large negative value. In fact, a very small region of the parameter space of this model, with small values of m{sub 0} and m{sub 1/2}, survives all the constraints at 95% C.L. It is remarkable that this specific region is still consistent with the lightest supersymmetric particle as the dark matter. Moreover, it predicts observable supersymmetric signals in the early runs of the LHC, even perhaps at 7 TeV. We also show that a consistent explanation for the deviation of the B{sup +{yields}{tau}+{nu}}{sub {tau}} branching ratio from the standard model can be achieved in a nonuniversal Higgs-mass model, which could also predict early signals of supersymmetry at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Vector bosons escaping from the brane: e{sup +}e{sup -}{yields}{gamma}+ nothing

We consider phenomenological consequences of the RS2-n model with an infinite extra dimension, namely, the production, in high-energy collisions, of a photon or Z boson escaping from our brane in association with a photon remaining on the brane. This would show up as process e{sup +}e{sup -}{yields}{gamma}+ nothing. We compare the signal with the standard model background coming from e{sup +}e{sup -}{yields}{gamma}{bar {nu}}{nu}. We also make a comparison with e{sup +}e{sup -}{yields}{gamma}+ nothing in the Arkani-Hamed-Dimopoulos-Dvali model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

First observation of radiative B⁰ → ΦK⁰γ decays and measurements of their time-dependent CP violation

We report the first observation of the radiative decay B⁰→ ΦK⁰γ using a data sample of 772 × 10⁶ BB¯ pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e⁻ collider. We observe a signal of 37 ± 8 events with a significance of 5.4 standard deviations including systematic uncertainties. The measured branching fraction is B(B⁰→ ΦK⁰γ) = (2.74±0.60±0.32)×10⁻⁶, where the uncertainties are statistical and systematic, respectively. We also report the first measurements of time-dependent CP-violation parameters: S ΦK⁰ S γ = +0.74 ⁺0.72 –1.05 (stat) +0.10 –0.24 (syst) and A ΦK⁰ S γ = +0.35 ± 0.58(stat) +0.23 –0.10 (syst). Furthermore, we measure B(B⁺ → ΦK⁺γ) = (2.48 ± 0.30 ± 0.24) × 10⁻⁶, ACP = –0.03 ± 0.11 ± 0.08 and find that the signal is concentrated in the M ΦK mass region near threshold.

Sahoo, Himansu B.↗
DOE OSTI2011

Analysis of the decay D{sup 0}{yields}K{sub S}{sup 0}{pi}{sup 0}{pi}{sup 0}

We present the results of a Dalitz plot analysis of D{sup 0}{yields}K{sub S}{sup 0}{pi}{sup 0}{pi}{sup 0} using the CLEO-c data set of 818 pb{sup -1} of e{sup +}e{sup -} collisions accumulated at {radical}(s)=3.77 GeV. This corresponds to 3x10{sup 6} D{sup 0}D{sup 0} pairs from which we select 1259 tagged candidates with a background of 7.5{+-}0.9 percent. Several models have been explored, all of which include the K{sup *}(892), K{sub 2}{sup *}(1430), K{sup *}(1680), the f{sub 0}(980), and the {sigma}(500). We find that the combined {pi}{sup 0{pi}0} S-wave contribution to our preferred fit is (28.9{+-}6.3{+-}3.1)% of the total decay rate while D{sup 0}{yields}K{sup *}(892){sup 0}{pi}{sup 0} contributes (65.6{+-}5.3{+-}2.5)%. Using three tag modes and correcting for quantum correlations we measure the D{sup 0}{yields}K{sub S}{sup 0}{pi}{sup 0}{pi}{sup 0} branching fraction to be (1.058{+-}0.038{+-}0.073)%.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Yielding transitions and grain-size effects in dislocation theory

The statistical-thermodynamic dislocation theory developed in previous papers is used in this paper in an analysis of yielding transitions and grain-size effects in polycrystalline solids. Calculations are based on the 1995 experimental results of Meyers, Andrade, and Chokshi [Metall. Mater. Trans. A 26, 2881 (1995)] for polycrystalline copper under strain-hardening conditions. The main assertion is that the well-known Hall-Petch effects are caused by enhanced strengths of dislocation sources at the edges of grains instead of the commonly assumed resistance to dislocation flow across grain boundaries. Finally, the theory describes rapid transitions between elastic and plastic deformation at yield points; thus it can be used to predict grain-size dependence of both yield stresses and flow stresses.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Particle-Yield Modification in Jetlike Azimuthal Dihadron Correlations in Pb-Pb Collisions at s_NN = 2.76 TeV

The yield of charged particles associated with high-p{sub t} trigger particles (8 < p{sub t} < 15 GeV/c) is measured with the ALICE detector in Pb-Pb collisions at {radical}s{sub NN} = 2.76 TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jetlike correlation peaks in azimuthal dihadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta p{sub t} > 3 GeV/c on the away side drops to about 60% of that observed in pp collisions, while on the near side a moderate enhancement of 20%-30% is found.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Yield Precursor Dislocation Avalanches in Small Crystals: The Irreversibility Transition

The transition from elastic to plastic deformation in crystalline metals shares history dependence and scale-invariant avalanche signature with other nonequilibrium systems under external loading such as colloidal suspensions. These other systems exhibit transitions with clear analogies to work hardening and yield stress, with many typically undergoing purely elastic behavior only after “training” through repeated cyclic loading; studies in these other systems show a power-law scaling of the hysteresis loop extent and of the training time as the peak load approaches a so-called reversible-to-irreversible transition (RIT). We discover here that deformation of small crystals shares these key characteristics: yielding and hysteresis in uniaxial compression experiments of single-crystalline Cu nano- and micropillars decay under repeated cyclic loading. Here, the amplitude and decay time of the yield precursor avalanches diverge as the peak stress approaches failure stress for each pillar, with a power-law scaling virtually equivalent to RITs in other nonequilibrium systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Beam Energy Dependence of Triton Production and Yield Ratio $N_t \times N_p / N^2_d$ in Au+Au Collisions at RHIC

We report the triton (t) production in midrapidity (|y| < 0.5) Au + Au collisions at $\sqrt{s_{NN}} = 7.7-200$ GeV measured by the STAR experiment from the first phase of the beam energy scan at the Relativistic Heavy Ion Collider. The nuclear compound yield ratio ($N_t \times N_p / N^2_d$), which is predicted to be sensitive to the fluctuation of local neutron density, is observed to decrease monotonically with increasing charged-particle multiplicity ($dN_{ch}/dη$) and follows a scaling behavior. The $dN_{ch}/dη$ dependence of the yield ratio is compared to calculations from coalescence and thermal models. Enhancements in the yield ratios relative to the coalescence baseline are observed in the 0%-10% most central collisions at 19.6 and 27 GeV, with a significance of 2.3σ and 3.4σ, respectively, giving a combined significance of 4.1σ. The enhancements are not observed in peripheral collisions or model calculations without critical fluctuation, and decreases with a smaller $p_T$ acceptance. The physics implications of these results on the QCD phase structure and the production mechanism of light nuclei in heavy-ion collisions are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗