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DOE OSTI2025

Complexity in the Photofunctionalization of Single-Wall Carbon Nanotubes with Hypochlorite

The reaction of aqueous suspensions of single-wall carbon nanotubes (SWCNTs) with UV-excited sodium hypochlorite has previously been reported to be an efficient route for doping nanotubes with oxygen atoms. Here, we have investigated how this reaction system is affected by pH level, dissolved O 2 content, and radical scavengers and traps. Products were characterized with near-IR fluorescence, Raman, and XPS spectroscopy. The reaction is greatly accelerated by removal of dissolved O 2 and strongly suppressed by TEMPO, a radical trap. Alcohols added as radical scavengers alter the reaction efficiency and the product peak emission wavelengths. Photofunctionalization with 300 nm irradiation is substantially less efficient at pH levels low enough to protonate the OCl – ion to HOCl. We deduce that in mildly treated high pH samples, the main product is sp 2 hybridized O-doped adducts formed by reaction of SWCNTs with atomic oxygen in its 3 P (ground) level. By contrast, treatment under low pH conditions leads to sp 3 hybridized SWCNT adducts formed by the addition of secondary radicals from reactions of • OH and • Cl. There is also evidence for additional photoreactions of product species under stronger irradiation. Researchers using photoexcited hypochlorite for SWCNT functionalization should be alert to the range of products and the sensitivity to reaction conditions in this system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1980

HEAO 1 observations of gamma-ray lines from a solar flare

HEAO 1 observed gamma radiation, including the 2.223 MeV line of deuterium and the 4.43 MeV line of C-12, from a white-light solar flare of 1978 July 11. Line strengths over a 4 minute integration were 1.00 + or - 0.29 and 0.18 + or - 0.07 photons/sq cm s, respectively, and the continuum in the 1-5 MeV range fitted a spectrum 10 E to the -3rd photons/sq cm s keV. The 2.2 MeV line lagged 94 + or - 30 s behind the gamma-ray continuum, which itself was delayed about 20 s from the hard X-ray (not less than 40 keV) and microwave fluxes. This is the second flare for which both MeV-range lines and continuum have been observed, and the first for which simultaneous white-light observations exist. The prompt gamma-ray line (4.43 MeV) can be directly interpreted as an energy deposition of not greater than 7 x 10 to the 26th ergs per sec by energetic protons at photospheric depths. This is insufficient to maintain the white-light continuum by normal photospheric emission mechanisms.

Hudson, H. S.↗

NASA NTRS1982

DE-2 cusp observations - Role of plasma instabilities in topside ionospheric heating and density fluctuations

Observations by the low altitude Dynamics Explorer satellite (DE-2) in the polar cusp show the ionospheric plasma electron temperature and the ratio of electron to ion temperature to be increased, and the electron density fluctuations to be enhanced. Also, downward fluxes of energetic eletrons and ions increase in the cusp, and the magnetic field structure are consistent with the existence of a field-aligned current. Simultaneously, there is characteristic broadband electrostatic noise (BEN) with amplitudes of 1-10 mV/m, peaking in the cusp but extending into the polar cap. These emissions range from far below the local 0(+) gyrofrequency F sub O(+) to the vicinity of the proton gyrofrequency, but below the oxygen lower hybrid frequency. The BEN observations are compared to the predictions of several theories. The amplitude of these waves is shown to be far too small to contribute significantly to the observed ionospheric heating or density fluctuations by local wave-particle interactions. Rather, the observed spatial variations are attributed to nonlocal field aligned heating processes and reflect the nonuniformity of the magnetosheath plasma's penetration into the ionosphere.

Curtis, S. A.↗

NASA NTRS1982

On the origin of relativistic particles and gamma-rays in quasars

A model for a class of quasars and active galactic nuclei is proposed in which a shock around a massive black hole randomizes the infall kinetic energy of spherically accreting matter producing a nonthermal spectrum of high energy protons. It is suggested that these protons are responsible for the secondary production (via proton decay) of the radio emitting high energy electrons and also of high energy gamma-rays (via proton decay and inverse Compton interactions of the electrons). The correlation between radio and gamma-ray emission implied by the model is in good agreement with observations of 3C273. Observation of the flux of high energy neutrinos from quasars may provide a test for the model.

Protheroe, R. J.↗

NASA NTRS1987

On the sources of solar energetic particles

We have examined the time histories of energetic (greater than 1 MeV) particles as detected by instruments in the earth's neighborhood over an 18 year period commencing mid-1967. The majority (greater than 75 percent) of the events extending to proton energies above 20 MeV have their origins in a flare event which includes H-alpha emission, soft x rays, and metric radio bursts of Type 2 and/or Type 4. We have assembled a list of 241 events for which the sources are thus well identified. Two further particle increases have been associated with nonflare events. Of the 82 events originating in regions to the east of central meridian, the sources of 68 (83 percent) were sufficiently energetic that they also generated interplanetary shocks detected at earth. We suggest that shocks are responsible for particles being detectable from source regions not magnetically connected to earth.

Cane, H. V↗

NASA NTRS2013

High-Energy Gamma-Ray Emission From Solar Flares: Summary of Fermi LAT Detections and Analysis of Two M-Class Flares

We present the detections of 19 solar flares detected in high-energy gamma rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its rst four years of operation. Interestingly, all ares are associated with fairly fast Coronal Mass Ejections (CMEs) and are not all powerful X-ray ares. We then describe the detailed temporal, spatial and spectral characteristics of the rst two long-lasting events: the 2011 March 7 are, a moderate (M3.7) impulsive are followed by slowly varying gamma-ray emission over 13 hours, and the 2011 June 7 M2.5 are, which was followed by gamma-ray emission lasting for 2 hours. We compare the Fermi-LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that a hadronic origin of the gamma rays is more likely than a leptonic origin and nd that the energy spectrum of the proton distribution softens after the 2011 March 7 are, favoring a scenario with continuous acceleration at the are site. This work suggests that proton acceleration in solar ares is more common than previously thought, occurring for even modest X-ray ares, and for longer durations.

fermi↗

NASA NTRS2018

Interplanetary Type II Radio Bursts from Wind/WAVES and Sustained Gamma-Ray Emission from Fermi/LAT: Evidence for Shock Source

We present quantitative evidence that interplanetary type II radio bursts and sustained gamma-ray emission (SGRE) events from the Sun are closely related. Out of about 30 SGRE events reported in Share et al. we consider 13 events that had a duration exceeding 5 hr to exclude any are-impulsive phase gamma-rays. The SGRE duration also has a linear relation with the ending frequency of the bursts. The synchronism between the ending times of SGRE and the type II emission strongly supports the idea that the same shock accelerates electrons to produce type II bursts and protons (>300 MeV) that propagate from the shock to the solar surface to produce SGRE via pion decay. The acceleration of high-energy particles is confirmed by the associated solar energetic particle (SEP) events detected at Earth and/or at the Solar Terrestrial Relations Observatory spacecraft. Furthermore, the presence of >300 MeV protons is corroborated by the fact that the underlying coronal mass ejections (CMEs) had properties identical to those associated with ground-level enhancement events: they had speeds of >2000 km s1 and all were full-halo CMEs. Many SEP events did not have detectable flux at Earth in the >300 MeV energy channels, presumably because of poor magnetic connectivity.

Gopalswamy, Nat↗

DOE OSTI2023

Systems and methods for monitoring fuel cell membrane degradation

Systems and methods for real-time continuous monitoring of fuel cell membrane degradation are provided. At least one microsensor can be used as an inline sensor integrated at the cathode exhaust and/or the anode exhaust of a fuel cell, such as a proton exchange membrane fuel cell (PEMFC)). The microsensor can monitor the PEMFC degradation status by sensing the emission of fluoride.

Dong, Dongmei↗

DOE OSTI2024

Systems and methods for monitoring fuel cell membrane degradation

Dong, Dongmei↗

NASA NTRS1994

Gamma-ray observations of Ophiuchus with EGRET: The diffuse emission and point sources

Observations of the Ophiuchus region made with the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) during the first 2 1/2 years of operation show the diffuse emission from the interstellar gas in Ophiuchus as well as variable emission from two point sources. The gamma-ray emission is modeled in terms of cosmic-ray interactions with atomic and molecular hydrogen in Ophiuchus and with low-energy photons along the line of sight. The model also includes the flux from the two point sources and an isotropic diffuse contribution. The cosmic-ray density is assumed to be uniform. The derived ratio of molecular hydrogen column density to integrated CO intensity is (1.1 +/- 0.2) x 10(exp 20) H-mols/sq cm (K km/s)(exp -1). At the sensitivity and resolution of the gamma-ray data, no variation of this ratio over the modeled region is discernible, nor are any regions of enhanced cosmic-ray density apparent. The model was fitted to seven narrow energy bands to obtain the energy depedence of the gamma-ray production function and the spectra of the point sources. The derived production function is in good agreement with theoretical calculations and the local cosmic-ray electron and proton spectra. The positions of the point sources were determined from maximum likelihood analysis of the gamma-ray emission observed in excess of the diffuse model. We identify one point source with the quasar PKS 1622-253, which has an average flux, E greater than 100 MeV, of (2.5 +/- 0.5) x 10(exp -7) photons/sq cm/s and photon spectral index -1.9 +/- 0.3. The other source, denoted GRO J1631-27, has not yet been identified at other wavelengths. Its average flux, E greater than 100 MeV, is (1.1 +/- 0.4) x 10(exp -7) photons/sq cm/s; however, its spectral index is poorly determined. The spectral index and intensity of the isotropic contribution to the model agree well with the extragalactic diffuse emission derived from the SAS 2 data.

Hunter, S. D.↗

NASA NTRS1993

A search for proton beams during flares on AU Microscopii

We report the results of a coordinated observing campaign on the active M dwarf star AU Mic. The purpose of the campaign was to search for evidence of proton beams during the impulsive phase of stellar flares and to determine whether the energy contained in these beams represented a significant fraction of the energy budget of the flare. During a total of 3.5 hr of monitoring a small flare was observed simultaneously by the HST, IUE, and the AAT. This event, which had a total optical + UV emission of 1.3 x 10 exp 32 ergs, occurred during the decay phase of a much larger event and showed no evidence for a proton beam with an energy greater than a few times 10 exp 29 ergs/s. This is comparable to the maximum energy flux released by the flare, though this energy release rate must occur over a time interval much shorter than that of the impulsive phase itself. We conclude that the proton beams may be capable of transporting some energy during the impulsive phase of a flare, but that they are unlikely to be the major contributor, at least for this particular event.

Robinson, R. D.↗

NASA NTRS1972

Relativistic electrons from the sun observed by IMP-4.

Evaluation of data obtained from the IMP-4 satellite concerning 0.3- to 12-MeV electrons from the sun between May 24, 1967, and May 2, 1969. Correlations with contemporary proton intensity increases at energies above 1 MeV are studied. The results of this study are the following: (1) the differential electron energy spectrum (0.3 to 12 keV) from solar flares appears to be a constant of the flare process, with the spectral index gamma = (-) 3.0 plus or minus 0.2; (2) particle emission from solar flares contains a prompt component, which is injected into the interplanetary medium beyond the sun and which is responsible for the diffusion characteristics of solar particle events, and a delayed component which is effectively contained in the lower solar atmosphere where it diffuses typically less than or equal to plus or minus 100 deg in longitude and gradually escapes into interplanetary space; the delayed component gives rise to the corotating features commonly observed after the impulsive and diffusive onset from the prompt component; (3) storage of electrons greater than 300 keV and protons greater than 1 MeV is essential to explain emission and propagation characteristics of solar particle events; and (4) the events with low proton/electron ratios all occur at least three weeks after the previous relativistic electron producing flare.

Simnett, G. M.↗

DOE OSTI2026

Field Emission Analysis in SRF Cavities for PIP-II Using GEANT4

Field emission (FE) remains a key limitation to achieving optimal performance and reliability in superconducting radiofrequency (SRF) cavities used in accelerator cryomodules. Addressing this challenge requires a detailed understanding of the generation and transport of FE-induced radiation; however, the absence of standardized measurement protocols complicates comparisons across different testing stages and facilities. This work presents initial steps toward a quantitative, systematic framework for analyzing FE-induced radiation using Geant4 simulations. We model four cavity types to be deployed in Fermilab’s Proton Improvement Plan-II (PIP-II) linac - HB650, LB650, SSR2, and SSR1 - to investigate radiation signatures and their dependence on emission conditions. By integrating simulation results with radiation diagnostics, our goal is to identify probable emission sites, enhance diagnostic accuracy, and optimize detector placement. Ultimately, this approach seeks to inform cavity preparation, assembly, and testing procedures, enabling the delivery of FE-free SRF cryomodules for PIP-II.

Wijethunga, Sajini [Fermilab] (ORCID:0000000287659↗

DOE OSTI2026

Field Emission Analysis in SRF Cavities for PIP-II Using GEANT4

Wijethunga, Sajini [Fermilab] (ORCID:0000000287659↗

DOE OSTI2022

Performance and Durability of Proton Exchange Membrane Vapor-Fed Unitized Regenerative Fuel Cells

With a growing demand for electricity, clean hydrogen production and usage can be an asset not only to mitigate emissions but for long-term energy storage as well. Hydrogen gas, a high-density energy carrier, can be made through electrolysis in charging mode and generate electricity via a fuel cell in discharging mode in a unitized regenerative fuel cell (URFC). While URFCs reduce cost by combining the charging and discharging modes into a singular device, switching between modes becomes burdensome, and water management is a major challenge. One way to mitigate these issues is to operate the entire system in the vapor phase. Vapor-phase operation simplifies the physics of the system but will introduce losses within the system, primarily ohmic and mass transport during the charging mode. In this study, we explore the performance of a Proton-Exchange-Membrane (PEM)-URFC under vapor-phase conditions and the impact of different PEMs, feed gases, and relative humidity on the performance and durability. By tailoring operating conditions and membrane, the vapor-URFC achieves a roundtrip efficiency of 42% and a lifetime of 50,000 accelerated stress test cycles for fully humidified feeds. Discussion of vapor-URFC for energy storage and extensions to look at various applications shows the promise of this technology.

25 ENERGY STORAGE↗

DOE OSTI2026

The next-generation particle x-ray temporal diagnostic for simultaneous time-resolved measurements of nuclear-burn and x-ray emission histories in support of basic-science and inertial confinement fusion experiments at OMEGA

The next-generation Particle X-ray Temporal Diagnostic (PXTD) has been implemented for simultaneous measurements of x-ray, charged particle, and neutron emission histories from a wide range of inertial confinement fusion and high energy density plasma experiments, demonstrating excellent timing accuracy and greatly improved experimental flexibility. The key changes to the previously fielded system are a redesigned set of thin foil filters in front of the scintillators and individual neutral density filters for each region of the detector. The fully implemented PXTD system can provide unique information about the evolution of ion and electron temperatures in multi-ion and kinetic-physics experiments, proton radiography experiments, and DT experiments executed at the OMEGA facility. The system has 35 ps time resolution and negligible relative timing uncertainty between measured emission history signals. The first use of the upgraded four-channel PXTD system during a set of D 3 He-filled silica-glass implosions on OMEGA captured electron temperatures with a minimum uncertainty of 0.5 keV and resolved both the relative timings and widths of neutron, proton, and x-ray peaks within a single recorded image.

Evans, T. E. [Massachusetts Inst. of Technology (M↗

NASA NTRS1983

First-order Fermi acceleration in solar flares as a mechanism for the second-step acceleration of prompt protons and relativistic electrons

Solar flare data from June 27, 1980 balloon-based observations were studied in terms of the hard X ray component. A temporal delay of 3 sec was observed for the X ray emissions above 235 keV. The delay occurred relative to the low-energy electrons and indicated a second acceleration stage. An estimation of the acceleration rate of the first-order Fermi process operating in a closed flare loop was found to be in agreement with the resulting data, including the acceleration of both protons and relativistic electrons. Additional support for the first-order Fermi process is noted in the fact that flares generally occur in magnetic loops, a condition which allows energetic particles to continually interact with the upward moving shock fronts. A correlation has also been observed between the delay times and the H-alpha areas, encouraging the interpretation that the delay times are the shock transit times.

Bai, T.↗

DOE OSTI2021

Probing the hadronic nature of the gamma-ray emission associated with Westerlund 2

ABSTRACT Star-forming regions have been proposed as potential Galactic cosmic ray accelerators for decades. Cosmic ray acceleration can be probed through observations of gamma-rays produced in inelastic proton–proton collisions at GeV and TeV energies. In this paper, we analyse more than 11 yr of Fermi–LAT data from the direction of Westerlund 2, one of the most massive and best-studied star-forming regions in our Galaxy. In particular, we investigate the characteristics of the bright pulsar PSR J1023–5746 that dominates the gamma-ray emission below a few GeV at the position of Westerlund 2 and the underlying extended source FGES J1023.3–5747. The analysis results in a clear identification of FGES J1023.3–5747 as the GeV counterpart of the TeV source HESS J1023-575, through its morphological and spectral properties. This identification provides new clues about the origin of the HESS J1023-575 gamma-ray emission, favouring a hadronic origin of the emission, powered by Westerlund 2, rather than a leptonic origin related to either the pulsar wind nebula associated with PSR J1023–5746 or the cluster itself. This result indirectly supports the hypothesis that star-forming regions can contribute to the cosmic ray sea observed in our Galaxy.

Mestre, Enrique↗