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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Unveiling the underlying interactions in Ta 2 NiSe 5 from photoinduced lifetime change

We present a generic procedure for quantifying the interplay of electronic and lattice degrees of freedom in photodoped insulators through a comparative analysis of theoretical many-body simulations and time- and angle-resolved photoemission spectroscopy (TR-ARPES) of the transient response of the candidate excitonic insulator Ta 2 NiSe 5 . Our analysis demonstrates that the electron-electron interactions dominate the electron-phonon ones. In particular, a detailed analysis of the TR-ARPES spectrum enables a clear separation of the dominant broadening (electronic lifetime) effects from the much smaller band-gap renormalization. Theoretical calculations show that the observed strong spectral broadening arises from the electronic scattering of the photoexcited particle-hole pairs and cannot be accounted for in a model in which electron-phonon interactions are dominant. The competing interactions were quantified using the scaling analysis in the weak fluence regime. We demonstrate that the magnitude of the weaker subdominant band-gap renormalization sensitively depends on the distance from the semiconductor/semimetal transition in the high-temperature state, which could explain the apparent contradictions between various TR-ARPES experiments. The analysis presented here indicates that electron-electron interactions play a vital role (albeit not the sole one) in stabilizing the insulating state, and establishes the comparison between lifetime and gap evolution as an important probe of correlated insulators.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Lifetime measurements in 102 Mo interpreted in the interacting boson model and the X(5) symmetry

Lifetimes of low-lying excited states in 102 Mo populated in the two-neutron transfer reaction 100 Mo ⁢( 18 O, 16 O)⁢ 102 Mo were measured using the recoil distance Doppler shift method at the IFIN-HH Tandem accelerator. Lifetimes of the $2^+_1$, $0^+_2$, $4^+_1$, $2^+_2$, $2^+_3$, $3^+_1$, $6^+_1$, ($0^+_3$), $4^+_2$, ($3^−_1$), and ($5^−_1$) states were obtained. The deduced electromagnetic transition strengths have been compared to calculations performed in the interacting boson model framework including models representing the U(5) and X(5) symmetries. It is found that 102 Mo lies between the U(5) limit and the X(5) critical point symmetry.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Spontaneous fission lifetimes from the minimization of self-consistent collective action

The spontaneous fission lifetime of 264 Fm has been studied within nuclear density functional theory by minimizing the collective action integral for fission in a two-dimensional quadrupole collective space representing elongation and triaxiality. The collective potential and inertia tensor are obtained self-consistently using the Skyrme energy density functional and density-dependent pairing interaction. The resulting spontaneous fission lifetimes are compared with the static result obtained with the minimum-energy pathway. We show that fission pathways strongly depend on assumptions underlying collective inertia. With the nonperturbative mass parameters, the dynamic fission pathway becomes strongly triaxial and it approaches the static fission valley. On the other hand, when the standard perturbative cranking inertia tensor is used, axial symmetry is restored along the path to fission; an effect that is an artifact of the approximation used.

Physics↗
DOE OSTI2019

Constraints on neutrino lifetime from the Sudbury Neutrino Observatory

The long baseline between Earth and the Sun makes solar neutrinos an excellent test beam for exploring possible neutrino decay. The signature of such decay would be an energy-dependent distortion of the traditional survival probability which can be fit for using well-developed and high-precision analysis methods. Here a model including neutrino decay is fit to all three phases of $^{8}\mathrm{B}$ solar neutrino data taken by the Sudbury Neutrino Observatory (SNO). This fit constrains the lifetime of neutrino mass state ${{\nu}}_{2}$ to be > $8.08\times{}{10}^{{-}5}\text{ }\text{ }\mathrm{s}/\mathrm{eV}$ at 90% confidence. An analysis combining this SNO result with those from other solar neutrino experiments results in a combined limit for the lifetime of mass state ${{\nu}}_{2}$ of > $1.92\times{}{10}^{{-}3}\text{ }\text{ }\mathrm{s}/\mathrm{eV}$ at 90% confidence.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Gigantic Surface Lifetime of an Intrinsic Topological Insulator

We report that the interaction between light and novel two-dimensional electronic states holds promise to realize new fundamental physics and optical devices. Here, we use pump-probe photoemission spectroscopy to study the optically excited Dirac surface states in the bulk-insulating topological insulator Bi 2 Te 2 Se and reveal optical properties that are in sharp contrast to those of bulk-metallic topological insulators. We observe a gigantic optical lifetime exceeding 4 μs (1 μs=10 ${-}$6 s) for the surface states in Bi 2 Te 2 Se, whereas the lifetime in most topological insulators, such as Bi2Se3, has been limited to a few picoseconds (1 ps=10 ${-}$12 s). Moreover, we discover a surface photovoltage, a shift of the chemical potential of the Dirac surface states, as large as 100 mV. Lastly, our results demonstrate a rare platform to study charge excitation and relaxation in energy and momentum space in a two-dimensional system.

36 MATERIALS SCIENCE↗
DOE OSTI2016

How to Reach a Thousand-Second in-Plane Polarization Lifetime with 0.97 - GeV / c Deuterons in a Storage Ring

Here, we observe a deuteron beam polarization lifetime near 1000 s in the horizontal plane of a magnetic storage ring (COSY). This long spin coherence time is maintained through a combination of beam bunching, electron cooling, sextupole field corrections, and the suppression of collective effects through beam current limits. This record lifetime is required for a storage ring search for an intrinsic electric dipole moment on the deuteron at a statistical sensitivity level approaching 10 -29 $e$ cm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Lifetime Measurements and Triple Coexisting Band Structure in S 43

Lifetime measurements of excited states in the neutron-rich nucleus 43 S were performed by applying the recoil-distance method on fast rare-isotope beams in conjunction with the Gamma-Ray Energy Tracking In-beam Nuclear Array. The new data based on γγ coincidences and lifetime measurements resolve a doublet of (3/2 - ) and (5/2 - ) states at low excitation energies. Results were compared to the π(sd)-ν(pf) shell model and antisymmetrized molecular dynamics calculations. The consistency with the theoretical calculations identifies a possible appearance of three coexisting bands near the ground state of 43 S: the K π =1/2 - band built on a prolate-deformed ground state, a band built on an isomer with a 1f$-1\atop{7/2}$ character, and a suggested excited band built on a newly discovered doublet state. The latter further confirms the collapse of the N=28 shell closure in the neutron-rich region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Baryon-Number Violation by Two Units and the Deuteron Lifetime

We calculate the lifetime of the deuteron with dimension-nine quark operators that violate baryon number by two units. We construct an effective field theory for |ΔB| = 2 interactions that give rise to neutron-antineutron (n– n¯) oscillations and dinucleon decay within a consistent power counting. We calculate the ratio of the deuteron lifetime to the square of the n– n¯ oscillation time up to next-to-leading order. Our result, which is analytical and has a quantified uncertainty, is smaller by a factor ≃2.5 than earlier estimates based on nuclear models, which impacts the indirect bound on the n– n¯ oscillation time and future experiments. We discuss how combined measurements of n– n¯ oscillations and deuteron decay can help to identify the sources of baryon-number violation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Floquet Prethermalization with Lifetime Exceeding 90 s in a Bulk Hyperpolarized Solid

Here, we report the observation of long-lived Floquet prethermal states in a bulk solid composed of dipolar-coupled 13 C nuclei in diamond at room temperature. For precessing nuclear spins prepared in an initial transverse state, we demonstrate pulsed spin-lock Floquet control that prevents their decay over multiple-minute-long periods. We observe Floquet prethermal lifetimes $T^{'}_{2}$≈90.9 s, extended >60 000-fold over the nuclear free induction decay times. The spins themselves are continuously interrogated for ~10 min, corresponding to the application of ≈5.8×10 6 control pulses. The 13 C nuclei are optically hyperpolarized by lattice nitrogen vacancy centers; the combination of hyperpolarization and continuous spin readout yields significant signal-to-noise ratio in the measurements. This allows probing the Floquet thermalization dynamics with unprecedented clarity. We identify four characteristic regimes of the thermalization process, discerning short-time transient processes leading to the prethermal plateau and long-time system heating toward infinite temperature. This Letter points to new opportunities possible via Floquet control in networks of dilute, randomly distributed, low-sensitivity nuclei. In particular, the combination of minutes-long prethermal lifetimes and continuous spin interrogation opens avenues for quantum sensors constructed from hyperpolarized Floquet prethermal nuclei.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Precise Measurement of the D s + Lifetime at Belle II

We measure the lifetime of the $D^+_s$ meson using a data sample of 207 fb -1 collected by the Belle II experiment running at the SuperKEKB asymmetric-energy e + e - collider. The lifetime is determined by fitting the decay-time distribution of a sample of 116 × 10 3 $D^+_s$ → φπ + decays. Our result is τ$D^+_s$ = (499.5 ± 1.7 ± 0.9) fs, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Lifetimes and spatio-temporal response of protein crystals in intense X-ray microbeams

Serial synchrotron-based crystallography using intense microfocused X-ray beams, fast-framing detectors and protein microcrystals held at 300 K promises to expand the range of accessible structural targets and to increase overall structure-pipeline throughputs. To explore the nature and consequences of X-ray radiation damage under microbeam illumination, the time-, dose- and temperature-dependent evolution of crystal diffraction have been measured with maximum dose rates of 50 MGy s −1 . At all temperatures and dose rates, the integrated diffraction intensity for a fixed crystal orientation shows non-exponential decays with dose. Non-exponential decays are a consequence of non-uniform illumination and the resulting spatial evolution of diffracted intensity within the illuminated crystal volume. To quantify radiation-damage lifetimes and the damage state of diffracting crystal regions, a revised diffraction-weighted dose (DWD) is defined and it is shown that for Gaussian beams the DWD becomes nearly independent of actual dose at large doses. An apparent delayed onset of radiation damage seen in some intensity–dose curves is in fact a consequence of damage. Intensity fluctuations at high dose rates may arise from the impulsive release of gaseous damage products. Accounting for these effects, data collection at the highest dose rates increases crystal radiation lifetimes near 300 K (but not at 100 K) by a factor of ∼1.5–2 compared with those observed at conventional dose rates. Improved quantification and modeling of the complex spatio-temporal evolution of protein microcrystal diffraction in intense microbeams will enable more efficient data collection, and will be essential in improving the accuracy of structure factors and structural models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Advanced Cell-Level Control for Extending Electric Vehicle Battery Pack Lifetime

A cell-level control approach for electric vehicle battery packs is presented that enhances traditional battery balancing goals to not only provide cell balancing but also achieve significant pack lifetime extension. These goals are achieved by applying a new life-prognostic based control algorithm that biases individual cells differently based on their state of charge, capacity and internal resistance. The proposed life control approach reduces growth in capacity mismatch typically seen in large battery packs over life while optimizing usable energy of the pack. The result is a longer lifetime of the overall pack and a more homogeneous distribution of cell capacities at the end of the first life for vehicle applications. Active cell balancing circuits and associated algorithms are used to accomplish the cell-level life extension objectives. This paper presents details of the cell-level control approach, selection and design of the active balancing system, and low-complexity state-of-charge, capacity, and series-resistance estimation algorithms. A laboratory prototype is used to demonstrate the proposed control approach. The prototype consists of twenty-one 25 Ah Panasonic lithium-Ion NMC battery cells from a commercial electric vehicle and an integrated BMS/DC-DC system that provides 750 W to the vehicle low voltage auxiliary loads.

25 ENERGY STORAGE↗
DOE OSTI2016

High-Performance and Traditional Multicrystalline Silicon: Comparing Gettering Responses and Lifetime-Limiting Defects

In recent years, high-performance multicrystalline silicon (HPMC-Si) has emerged as an attractive alternative to traditional ingot-based multicrystalline silicon (mc-Si), with a similar cost structure but improved cell performance. Herein, we evaluate the gettering response of traditional mc-Si and HPMC-Si. Microanalytical techniques demonstrate that HPMC-Si and mc-Si share similar lifetime-limiting defect types but have different relative concentrations and distributions. HPMC-Si shows a substantial lifetime improvement after P-gettering compared with mc-Si, chiefly because of lower area fraction of dislocation-rich clusters. In both materials, the dislocation clusters and grain boundaries were associated with relatively higher interstitial iron point-defect concentrations after diffusion, which is suggestive of dissolving metal-impurity precipitates. The relatively fewer dislocation clusters in HPMC-Si are shown to exhibit similar characteristics to those found in mc-Si. Given similar governing principles, a proxy to determine relative recombination activity of dislocation clusters developed for mc-Si is successfully transferred to HPMC-Si.

14 SOLAR ENERGY↗
DOE OSTI2018

Moving Beyond p-Type mc-Si: Quantified Measurements of Iron Content and Lifetime of Iron-Rich Precipitates in n-Type Silicon

N-type multicrystalline silicon (mc-Si) is a promising alternative to the dominant p-type mc-Si for solar cells because it combines the cost advantages of mc-Si while benefiting from higher tolerance to transition metal contamination. A detailed understanding of the relative roles of point defect and precipitated transition metals has enabled advanced processing and high minority carrier lifetimes in p-type mc-Si. This contribution extends that fundamental understanding to Fe contamination in n-type mc-Si, helping enable processing of this material into an economical and high-performance photovoltaic device. Finally, by directly correlating micro-photoluminescence-based minority carrier lifetime mapping and synchrotron-based micro-X-ray fluorescence mapping of Fe-rich precipitates, we develop a quantitative, physical understanding of the recombination activity of Fe-rich precipitates in n-type mc-Si.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Impact of Carrier Concentration and Carrier Lifetime on MgZnO/CdSeTe/CdTe Solar Cells

Here, the performance impact of multiple parameters related to the use of MgZnO (MZO) as the emitter for bilayer CdSeTe/CdTe solar cells has been investigated in detail through numerical simulations. Such a comprehensive study is particularly important, because while cell fabrication using MZO has been highly successful in some cases, it has been less so in others, and it has not been clear which combinations of parameter values are most effective. The parameters considered here include the recombination velocity at the emitter/absorber interface, bulk recombination lifetime, and the carrier concentrations of the emitter and absorber. The ranges chosen for the simulation parameters are those most likely to be found experimentally. The primary finding is that independent of the interfacial recombination velocity and bulk recombination lifetime, the MZO carrier density should be > 1017 cm-3 and in any case greater than that of the absorber to reduce interface recombination. At the same time, a shallow dopant the order of 50 meV or less should reduce SRH recombination in the bulk and enable VOC > 1V.

14 SOLAR ENERGY↗
DOE OSTI2018

A Bayesian Approach for Extracting Fluorescence Lifetimes from Sparse Data Sets and Its Significance for Imaging Experiments

The measurement of fluorescence lifetimes, especially in small sample volumes, presents the dual challenge of probing a small number of fluorophores and fitting the concomitant sparse data set to the appropriate excited-state decay function. A common method of analysis, such as the maximum likelihood (ML) technique, assumes a uniform probability distribution of the parameters describing the fluorescence decay function. An improvement is thus suggested by implementing a suitable nonuniform distribution, as is provided by a Bayesian framework, where the distribution of parameters is obtained from both their prior knowledge and the evidence-based likelihood of an event for a given set of parameters. We have also considered the Dirichlet prior distribution, whose mathematical form enables analytical solutions of the fitting parameters to be rapidly obtained. If Gaussian and exponential prior distributions are judiciously chosen, they reproduce the experimental target lifetime to within 20% with as few as 20 total photon counts for the data set, as does the Dirichlet prior distribution. But because of the analytical solutions afforded by the Dirichlet prior distribution, it is proposed to employ a Dirichlet prior to search parameter space rapidly to provide, if necessary, appropriate parameters for subsequent employment of a Gaussian or exponential prior distribution

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Dispersion of Lifetimes of Excited States of Single Molecules in Organic Matrices at Ultralow Temperatures

Fluorescence excitation spectra of single terrylene molecules in transparent naphthalene and polyethylene matrices at ultralow (30–100 mK) temperatures have been studied under the conditions where the widths of zero-phonon spectral lines are determined only by the lifetime T{sub 1} of the excited electronic state. The experimentally observed dispersion of T{sub 1} values for identical molecules is attributed to local field effects, which are responsible for the dependence of T{sub 1} on the effective value of refractive index n of the matrix, which is characteristic of the localization region of each molecule. It has been shown that the dependence T{sub 1}(n) for ensembles of point emitters in organic matrices is satisfactorily explained within the model of a “virtual cavity” around the emitter inside a continuous medium, as well as within the developed quantum kinetic approach including various contributions of the local environment to the lifetime T{sub 1}. The recalculation of average T{sub 1} values to the corresponding n values with the use of the expressions obtained for T{sub 1}(n) has shown that the difference of the calculated refractive indices of naphthalene and polyethylene from the well-known tabulated n values is less than 1%.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Calculation of Prompt Fission Neutron Lifetimes by the Monte Carlo Method

An algorithm for calculation of prompt fission neutron lifetimes in a nuclear reactor by the Monte Carlo method is described. Evaluation of the importance function is carried out with solution of the neutron transport equation without solving the adjoint equation. The results of the prompt neutron lifetime calculations performed within some critical experiments are presented and compared with the experimental results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗