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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane

The center of our Galaxy is a known strong source of electron-positron 511- keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic Plane. No positive annihilation flux was detected outside of the central region (|l| greater than 40 degrees) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511-keV flux.

Teegarden, B. J.↗
NASA NTRS2007

Scattering of Low Energy Electrons and Positrons from Hydrogenic Systems and Applications

While the electron scatters from the target, the target no longer stays in its original form. One of the first methods to take into account the distortion of the target at low incident energies is the method of polarized orbitals. In this method the wave function for the process is written using the first-order perturbation theory and the equation for the scattering function is derived from the Schradinger equation. This method has been very successful in calculating the phase shifts and therefore the cross sections at various energies. The total wave function can be used to calculate photoionization cross sections. The disadvantage of this approach is that the method is not variational and therefore does not provide bounds on the phase shifts. These difficulties can be overcome by using the Feshbach projection operator formalism. This approach has been employed for the scattering of electrons and positrons from targets. Results of various calculations will be discussed.

Bhatia, Anand K.↗
NASA NTRS2018

Optically Inaccessible Flow Visualization using Positron Emission Tomography

Flow visualization is a powerful tool for characterizing fluid dynamics within engineering systems that utilize fluid working media. Recent advances in Positron Emission Tomography (PET) have enhanced its ability to extend beyond the medical field, and offer an alternate vantage point in visualizing optically inaccessible fluid distributions and flow fields within the aerospace field. In light of this prospect an investigation has ensued to parametrically bound the flows that can be sufficiently resolved using current PET technology. Preliminary results from on going simulations and analyses will be presented.

Bruggemann, Jeremy↗
DOE OSTI2015

The extent of non-thermal particle acceleration in relativistic, electron-positron reconnection

Reconnection is studied as an explanation for high-energy flares from the Crab Nebula. The production of synchrotron emission >100 MeV challenges classical models of acceleration. 3D simulation shows that reconnection, converting magnetic energy to kinetic energy, can accelerate beyond γ rad . The power-law index and high-energy cutoff are important for understanding the radiation spectrum dN/dγ = f(γ) ∝ γ -α . α and cutoff were measured vs. L and σ, where L is system (simulation) size and σ is upstream magnetization (σ = B 2 /4πnmc 2 ). α can affect the high-energy cutoff. In conclusion, for collisionless relativistic reconnection in electron-positron plasma, without guide field, n b /n d =0.1: (1) relativistic magnetic reconnection yields power-law particle spectra, (2) the power law index decreases as σ increases, approaching ≈1.2. (3) the power law is cut off at an energy related to acceleration within a single current layer, which is proportional to the current layer length (for small systems, that length is the system length, yielding γ c2 ≈ 0.1 L/ρ 0 ; for large systems, the layer length is limited by secondary tearing instability, yielding γ c1 ≈ 4σ; the transition from small to large is around L/ρ 0 = 40σ.). (4) although the large-system energy cutoff is proportional to the average energy per particle, it is significantly higher than the average energy per particle.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Systems and methods for point-of-care positron emission tomography

A positron emission tomography (PET) system is provided. The system includes a first detector panel including a first array of detectors, a second detector panel including a second array of detectors, said second detector panel being moveable relative to a point between the first detector panel and the second detector panel, a tracking system configured to detect a position of said second detector panel relative to the first detector panel while imaging a subject, a computing device in communication with the first detector panel, the second detector panel, and the tracking system, the computing device configured to receive coincidence data from the first and second detector panels, receive position data from the tracking system, wherein each coincidence datum of the received coincidence data is associated with a unique position datum of the received position data, and reconstruct a plurality of images based on the received coincidence data and the received position data.

Tai, Yuan-Chuan↗
DOE OSTI2015

Investigation of the process e{sup +}e{sup −} → K{sup +}K{sup −} with the aid of the CMD-3 detector at the VEPP-2000 electron-positron collider

Preliminary results of an experiment that is aimed at measuring the cross section for the process e{sup +}e{sup −} → K{sup +}K{sup −} at c.m. energies in the range between 1.01 and 2.0 GeV with the aid of the CMD-3 detector and which is being performed at the VEPP-2000 collider of the Budker Institute of Nuclear Physics (Novosibirsk, Siberian Branch, Russian Academy of Sciences) are presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Hepatotoxic Dose Thresholds by Positron-Emission Tomography After Yttrium-90 Radioembolization of Liver Tumors: A Prospective Single-Arm Observational Study

PurposeTo define a threshold radiation dose to non-tumoral liver from {sup 90}Y radioembolization that results in hepatic toxicity using pair-production PET.Materials and MethodsThis prospective single-arm study enrolled 35 patients undergoing radioembolization. A total of 34 patients (27 with HCC and 7 with liver metastases) were included in the final analysis. Of 27 patients with underlying cirrhosis, 22 and 5 patients were Child–Pugh A and B, respectively. Glass and resin microspheres were used in 32 (94%) and 2 (6%) patients, respectively. Lobar and segmental treatment was done in 26 (76%) and 8 (24%) patients, respectively. Volumetric analysis was performed on post-radioembolization time-of-flight PET imaging to determine non-tumoral parenchymal dose. Hepatic toxicity was evaluated up to 120 days post-treatment, with CTCAE grade ≤ 1 compared to grade ≥ 2.ResultsThe median dose delivered to the non-tumoral liver in the treated lobe was 49 Gy (range 0–133). A total of 15 patients had grade ≤ 1 hepatic toxicity, and 19 patients had grade ≥ 2 toxicity. Patients with a grade ≥ 2 change in composite toxicity (70.7 vs. 43.8 Gy), bilirubin (74.1 vs. 43.3 Gy), albumin (84.2 vs. 43.8 Gy), and AST (94.5 vs. 47.1 Gy) have significantly higher non-tumoral parenchymal doses than those with grade ≤ 1. Liver parenchymal dose and Child–Pugh status predicted grade ≥ 2 toxicity, observed above a dose threshold of 54 Gy.ConclusionIncreasing delivered {sup 90}Y dose to non-tumoral liver measured by internal pair-production PET correlates with post-treatment hepatic toxicity. The likelihood of toxicity exceeds 50% at a dose threshold of 54 Gy.ClinicalTrials.gov identifier: NCT02848638.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Early risk stratification using Rubidium-82 positron emission tomography in STEMI patients

Background: Assessment of infarct size after myocardial infarction is predictive of subsequent morphological changes and clinical outcome. This study aimed to assess subacute post-intervention Rubidium-82 ({sup 82}Rb)-PET imaging in predicting left ventricle ejection fraction, regional wall motion, and final infarct size by CMR at 3-months after STEMI. Methods: STEMI patients undergoing percutaneous coronary intervention were included prospectively. Rest-only {sup 82}Rb-PET perfusion imaging was performed at median 36 hours [IQR: 22 to 50] after the treatment. The extent of hypoperfusion and absolute blood flow (mL·min·g) were estimated on a global and a 17-segment model with dedicated software. At 3-months follow-up patients completed the CMR functional and late gadolinium enhancement imaging. Results: 42 patients were included, but only 35 had follow-up CMR and constituted the study population. Absolute blood flow was significantly lower in the infarct-related territory compared to remote myocardium, P < .005. Extent of hypoperfusion correlated with final infarct size, r = 0.58, P < .001, while blood flow correlated with ejection fraction, r = 0.41, P < .05. In linear mixed models, higher subacute absolute blood flow (β = 4.6, confidence interval [3.5; 5.2], P < .001, R{sup 2} = 0.67) was associated with greater wall motion. Segmental extent of subacute hypoperfusion (β = 0.43 [0.38; 0.49], P < .001, R{sup 2} = 0.58) was associated with the degree of late gadolinium enhancement at 3-months. Conclusions: Subacute rest-only {sup 82}Rb-PET is feasible following STEMI and seems predictive of myocardial function and infarct size at 3-months.

62 RADIOLOGY AND NUCLEAR MEDICINE↗