National Institute of Standards and Technology
Recent publications
The x-ray spectroscopy of the muonic atom has attracted atomic, nuclear, and particle physicists since its discovery. The properties of a muonic atom, such as its binding energy or atomic radius, are different from an ordinary atom because of the difference in the mass between the muon and electron. Our collaboration has employed superconductor transition-edge sensor (TES) microcalorimeters for the x-ray spectroscopy of the muonic atom. Thanks to the recent detector development, the 44-keV lines from muonic Ar, which is important for the precision test of bound-state quantum electrodynamics, and the 76-keV lines from muonic Si, which is of interest from the viewpoint of the measurement of nuclear radii, have been reached by the dynamic range of the state-of-art TES microcalorimeters. An accelerator facility that can produce a high-intensity muon beam is necessary for such spectroscopic experiments. We performed a commissioning experiment of the hard x-ray and gamma-ray TES microcalorimeter at the J-PARC MLF MUSE muon beam line. The energy resolution, gain stability, and performance of timing selection of the pulses were evaluated in the environment of a large-scale accelerator facility.
Sub-1 AMU mass determination is important for determining fission yields and neutron multiplicity, which are necessary inputs for fission models. Fission models can improve spent nuclear waste stream analysis and nuclear fuel burnup determination. To achieve this goal, we have used superconducting microcalorimeter detectors to directly measure the energy of fission fragments from the spontaneous fission of 252 Cf. With a fiber coupled LED pulser setup we demonstrate that we can reach a relative energy resolution of 0.1% and better for photon pulses with energies above 60 MeV. This instrument, in conjunction with time-of-flight (TOF) measurement, would allow for sub-1 atomic mass unit (AMU) mass determination of fission fragments in a future beamline application.
This project explores the design and development of a transition edge sensor (TES) spectrometer for resonant soft X-ray scattering (RSXS) measurements developed in collaboration between Argonne National Laboratory (ANL) and the National Institute of Standards and Technology (NIST). Soft X-ray scattering is a powerful technique for studying the electronic and magnetic properties of materials on a microscopic level. However, the lack of high-performance soft X-ray spectrometers has limited the potential of this technique. TES spectrometers have the potential to overcome these limitations due to their high energy resolution, high efficiency, and broad energy range. This project aims to optimize the design of a TES spectrometer for RSXS measurements and more generally soft X-ray spectroscopy at the Advanced Photon Source (APS) 29-ID, leading to improved understanding of advanced materials. We will present a detailed description of the instrument design and implementation. The spectrometer consists of a large array of approximately 250 high-speed and high-resolution pixels. The pixels have saturation energies of approximately 1 keV, sub-ms pulse duration and energy resolution of approximately 1 eV. The array is read out using microwave multiplexing chips with MHz bandwidth per channel, enabling efficient data throughput. To facilitate measurement of samples in situ under ultra-high vacuum conditions at the beamline, the spectrometer is integrated with an approximately 1 m long snout.
Background We estimated the impact of screening on morbidity and mortality of HPV16-positive oropharyngeal cancer among US men aged 45-79 years. Methods We developed an individual-level, state-transition natural history microsimulation model to estimate the impact of screening using oral HPV16 detection, HPV16-E6 antibody detection, and transcervical-ultrasound of neck/oropharynx. We compared clinical detection to counterfactual screen detection for cancer stage, single- vs multiple-modality treatment, and survival. Screening scenarios encompassed four progression speeds across cancer stages (very-slow, slow, fast, and very-fast) and four screening frequencies. Results Among US men aged 45-79 years in 2021 (N = 54,881,311), 163,958 clinically diagnosed HPV-positive oropharyngeal cancers and 32,009 deaths would occur through age 84 in the absence of screening. Assuming very-fast progression, 4%, 20%, 31%, and 60% of these cancers would be detected by one-off, 5-yearly, 3-yearly, and annual screening. Annual screening (very-fast progression) could reduce the number of cancers diagnosed at advanced stages (AJCC 7, Stages III/IV: 90.0% with no screening vs 59.1%) and treated by multiple-modalities (80.6% with no screening vs 50.6%). Cancer mortality would also be reduced by 36.2%, with a gain of 106,000 life-years. Annual screening would have a number needed to screen (NNS) of 561 per screen-detected cancer, 1,118 per additional cancer treated by single-modality, 4,740 per death prevented, and 520 per life-year gained; such high NNS reflect potential inefficiency of population-level screening. Conclusions If proven efficacious in randomized trials and cost-effective, screening for HPV-positive oropharyngeal cancers could provide considerable population-level reductions in advanced stage cancers, treatment-related morbidities, and mortality.
This study characterizes the presence of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (BTMPS) in the illicit fentanyl supply in 9 US locations.
The precise control of mechanochemical activation within deep tissues using non-invasive ultrasound holds profound implications for advancing our understanding of fundamental biomedical sciences and revolutionizing disease treatments1, 2, 3–4. However, a theory-guided mechanoresponsive materials system with well-defined ultrasound activation has yet to be explored5,6. Here we present the concept of using porous hydrogen-bonded organic frameworks (HOFs) as toolkits for focused ultrasound (FUS) programmably triggered drug activation to control specific cellular events in the deep brain, through on-demand scission of the supramolecular interactions. A theoretical model is developed to potentially visualize the mechanochemical scission and ultrasound mechanics, providing valuable guidelines for the rational design of mechanoresponsive materials to achieve programmable control. To demonstrate the practicality of this approach, we encapsulate the designer drug clozapine N-oxide (CNO) into the optimal HOF nanocrystals for FUS-gated release to activate engineered G-protein-coupled receptors in the ventral tegmental area (VTA) of mice and rats and hence achieve targeted neural circuit modulation even at depth 9 mm with a latency of seconds. This work demonstrates the capability of ultrasound to precisely control molecular interactions and develops ultrasound-programmable HOFs to non-invasively and spatiotemporally control cellular events, thereby facilitating the establishment of precise molecular therapeutic possibilities.
Spin moiré superlattices (SMSs) have been proposed as a magnetic analog of crystallographic moiré systems and a source of electron minibands offering vector-field moiré tunability and Berry curvature effects. However, it has proven challenging to realize an SMS in which a large exchange coupling J is transmitted between conduction electrons and localized spins. Furthermore, most systems have carrier mean free paths l mfp shorter than their spin moiré lattice constant a spin , inhibiting miniband formation. Here, we discover that the layered magnetic semimetal EuAg 4 Sb 2 overcomes these challenges by forming an interface with J ~ 100 milli–electron volts transferred between a Eu triangular lattice and anionic Ag 2 Sb bilayers hosting a two-dimensional electron band in the ballistic regime ( l mfp >> a spin ). The system realizes an SMS with a spin commensurate with the Fermi momentum, leading to a marked quenching of the transport response from miniband formation. Our findings demonstrate an approach to magnetically engineering moiré superlattices and a potential route to an emergent spin-driven quantum Hall state.
Conjugated polymers can undergo complex, concentration‐dependent self‐assembly during solution processing, yet little is known about its impact on film morphology and device performance of organic solar cells. Herein, lyotropic liquid crystal (LLC) mediated assembly across multiple conjugated polymers is reported, which generally gives rise to improved device performance of blade‐coated non‐fullerene bulk heterojunction solar cells. Using D18 as a model system, the formation mechanism of LLC is unveiled employing solution X‐ray scattering and microscopic imaging tools: D18 first aggregates into semicrystalline nanofibers, then assemble into achiral nematic LLC which goes through symmetry breaking to yield a chiral twist‐bent LLC. The assembly pathway is driven by increasing solution concentration – a common driving force during evaporative assembly relevant to scalable manufacturing. This assembly pathway can be largely modulated by coating regimes to give 1) lyotropic liquid crystalline assembly in the evaporation regime and 2) random fiber aggregation pathway in the Landau–Levich regime. The chiral liquid crystalline assembly pathway resulted in films with crystallinity 2.63 times that of films from the random fiber aggregation pathway, significantly enhancing the T80 lifetime by 50‐fold. The generality of LLC‐mediated assembly and enhanced device performance is further validated using polythiophene and quinoxaline‐based donor polymers.
With sufficiently high signal-to-noise, several systematic errors become prominent in dual-comb interferometry measurements. This paper reviews several error sources including electrical, photo-detection, amplification and acquisition chain non-linearity. Sources of optical non-linearity such as self-phase modulation, cross-phase modulation and Raman soliton shifting are also covered, as are spectral fringing due to parasitic reflections and back-scattering. The non-linear response of the target sample itself can also be a source of errors. Methods to identify and minimize errors in experimental data are discussed. Good practices, instrument design strategies and tools, such as the dynamic range diagram, are suggested.
This work considers the effects of changes in distance, centering and tilting of optical elements on radiometric throughput. Analytical formulas for leading-order effects are compared to numerical calculations for validation purposes.
The National Physical Laboratory (United Kingdom) and the National Institute of Standards and Technology (United States) each determined the massic activity of a common solution of ²²⁷Th. Measurements at both laboratories were performed before radioactive equilibrium. The direct comparison showed good accord between the laboratories’ activity standards with a t-test score of 0.15 based on ionization chamber measurements. Challenges associated with pre-equilibrium comparisons are addressed and multiple comparison approaches are presented. The use of a hybrid comparison methodology using a model to correct asynchronously acquired data to an intermediate timepoint mitigates major sources of uncertainty and potential bias in extreme cases.
The volume of global e-waste is much greater than the volume of recycled e-waste. Increased awareness and improved management of e-waste are crucial.
Artificial neural networks have advanced due to scaling dimensions, but conventional computing struggles with inefficiencies due to memory bottlenecks. In-memory computing architectures using memristor devices offer promise but face challenges due to hardware non-idealities. This work proposes layer ensemble averaging—a hardware-oriented fault tolerance scheme for improving inference performance of non-ideal memristive neural networks programmed with pre-trained solutions. Simulations on an image classification task and hardware experiments on a continual learning problem with a custom 20,000-device prototyping platform show significant performance gains, outperforming prior methods at similar redundancy levels and overheads. For the image classification task with 20% stuck-at faults, accuracy improves from 40% to 89.6% (within 5% of baseline), and for the continual learning problem, accuracy improves from 55% to 71% (within 1% of baseline). The proposed scheme is broadly applicable to accelerators based on a variety of different non-volatile device technologies.
Laser Doppler anemometers (LDAs) use scattered light to determine velocity components of a flowing fluid. The operating principal of LDAs is simple conceptually; however, it is impractical to trace the LDA-determined velocities to the SI by characterizing the LDA’s subsystems that generate, detect, and process optical signals because these subsystems are complex and include proprietary features. To circumvent this, we calibrated the complete LDA systems utilizing an optical chopper blade as an accurate, SI-traceable velocity standard. The calibrations achieved the expanded velocity uncertainty 0.094% at a 95% confidence level. We calibrated two LDAs that differed in manufacturer, focal length (in the ratio 3.3:1), sensing volume (in the ratio 100:1), and orientation (vertical and horizontal bisectors of the LDA’s crossing beams). To compare the calibrations, we measured airspeeds in NIST’s wind tunnel using both LDAs. The results differed from each other by, at most, 0.2% throughout the airspeed range (0.5–30) m s⁻¹.
Like planets in the solar system, exoplanets form, evolve, and interact with their host stars in many ways. Exoplanets form out of protostellar disks, which contain positive ions (H+{ }^+, H2++{ }_2^++, and H3+{ }_3^+) and other radicals produced when molecules in the disk are photo-dissociated by stellar UV and X-ray photons and then charge-exchanged by protons in the stellar wind. These positive ions become the formation seeds of complex molecules including simple organics.
If stars were uniformly bright across their surfaces, the analysis of transit observations would require only the subtraction of this bright background from the observed data, resulting in the transit light curve and the absorption spectrum produced by atoms and molecules in the exoplanet’s atmosphere. Even this unrealistically simple observing scenario is a data analysis challenge, because the area of a transiting planet may be only 1% or smaller than that of the host star, and the area of a terrestrial exoplanet’s atmosphere seen in absorption against the stellar disk may be only 0.01% that of the stellar disk area. Thus high signal/noise data are essential to minimize random noise.
In Chaps. 10 and 11, I surveyed the various ways in which a host star’s radiation and wind can erode an exoplanet’s atmosphere, change its chemistry, and thereby determine whether the exoplanet could be habitable. I now turn to the question of whether an exoplanet can change the properties of its host star, in particular, its rotation rate, UV and X-ray radiation, and the properties of its wind. The study of this feedback of an exoplanet on its host star is usually called star-planet interactions (SPI), although a more accurate term would be planet-star interactions.
Exoplanets have intimate relationships with their host stars as the Earth does with its host star. While the Earth’s environment produced by the Sun is usually benign, exoplanets located close to their host stars, especially active M dwarfs, must suffer through powerful flares, stellar winds, CMEs, and very high energy radiation. The environment in which exoplanets must live is now called “stellar space weather” in analogy with the extensively monitored “space weather” that is the environment of the Earth. In this chapter I describe flares and superflares on the Sun and stars and how repeated flares destroy O3{ }_3 in the atmospheres of exoplanets possibly leading to the sterilization of their surfaces and loss of habitability.
An important technique for determining an exoplanet’s mass is the measurement of the orbital semi-major axis. This comes from radial velocity (RV) measurements, together with estimates of stellar mass and the inclination of the orbit relative to the line of sight. If the exoplanet also transits its host star, then the resulting measurement of the exoplanet’s radius yields a value for density and likely chemical composition. Limitations on the accuracy and precision of RV measurements, both stellar and instrumental, degrade orbital determinations and thus the inferred properties of the exoplanet. There are at least four sources of RV jitter (also called stellar noise) from solar-like stars: granulation, supergranulation, magnetic effects on flow patterns, and pulsations. An additional source of RV jitter is instrumental including the limitations of data analysis software. This chapter explores each RV noise source and the limitations that the sum of these sources place on the ability to identify an exoplanet from radial velocity measurements. Several very different approaches have been developed to characterize and minimize the sources of RV noise.
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Paul Lemaillet
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Gaithersburg, United States
Head of institution
Dr. Walter Copan