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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Alpha/beta-gated gamma–gamma spectroscopy of mixed fission products for trace analysis

This experiment demonstrated that some hard-to-detect fission products can be quantified directly from mixed fission product samples using advanced radio-emission spectroscopy techniques. A gamma/gamma coincidence detector was combined with a custom liquid scintillation counter to evaluate the benefits of alpha and beta coincident and anti-coincident analysis of mixed fission product samples. Reduction factors in the minimum detectable activity (MDA) relative to traditional gamma counting were quantified for a set of radionuclides. For isotopes like 91Y, 144Ce, 147Nd, and 153Sm MDA reductions of factors of 1-2 were observed using optimized beta thresholds. Using beta anti-coincidence counting reductions of factors 3-5 were observed for isotopes like 89Sr, 95mNb, 115Cd, and 137Cs and factors of 5-7 for isotopes like 235U using alpha coincidence counting. The selectivity of gamma/gamma coincidence and reduction in backgrounds using beta gating were also demonstrated with 136Cs and 153Sm. The improvements observed in the detection sensitivity of fission products and actinides achieved by combining time-correlated radiation signatures is significant and of value to applications such as nuclear fission physics, environmental monitoring for nuclear waste, reactor accidental releases, and nuclear forensics.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Time sequence gamma-spectrometry of irradiated salt

Persisted Memory Mapping File (MMF) techniques have developed for the processing and analysis of time-stamped list (TLIST) mode data collected from an irradiated salt sample. This is a new technique that is unique to this research and enables additional information to be obtained from a conventional pulse height analysis (PHA) gamma-spectrometry acquisition. A salt sample was irradiated using a DT neutron generator and immediately measured using TLIST acquisition for 1 month to generate a 22 GB data file. MMF techniques were used to process the file without size restrictions at a rate of 388.5 MB minute-1, with instant access to any position within the file, separating the file into a series of time sequenced spectra suitable for PHA analysis. This enabled 14 activation products to be identified at different time intervals (41Ar, 80Br, 80mBr, 47Ca, 34mCl, 38Cl, 42K, 43K, 56Mn, 22Na, 24Na, 85Sr, 87mSr and 69mZn), and 6 radionuclides (80Br, 47Ca, 34mCl, 56Mn, 24Na and 87mSr) to be definitively confirmed based upon their measured half-life. Using this technique, the detection of 47Ca, and in-growth of its 47Sc progeny, was demonstrated as useful for calculating the time since irradiation.

Burnett, Jonathan L.↗
DOE OSTI2019

H Atom Production and Reaction in the Gamma Radiolysis of Thermally Modified Boehmite

The correlation between the formation of H atoms and H2 was observed in the radiolysis of thermally modified boehmite (?-AlOOH). Boehmite was pretreated by heating to 300, 400, and 550°C, loaded with adsorbed water, and irradiated with gamma rays. Long-lived H atoms trapped in the interstitial matrix was observed by electron paramagnetic resonance techniques and the amount of gaseous H2 by gas chromatography. Heating the boehmite to 400°C before radiolysis results in the collapse of the matrix with loss of trapped H atoms and a substantial increase in the production of H2. Samples without added water post-heating showed no production of H2 suggesting that it is formed by the diffusion of H atoms to the surface followed by an abstraction reaction with water. Boehmite heated to 550°C has completely converted to alumina and the radiolytic responses of each are similar. Post-irradiation heating of boehmite to 300°C results in a doubling of the H2 yield at pretreated temperatures below 300°C due to the release of trapped H atoms.

La Verne, Jay A.↗
DOE OSTI2025

New determination of the millisecond pulsar gamma-ray luminosity function and implications for the Galactic Center gamma-ray excess

It has been suggested that the Galactic Center gamma-ray excess (GCE) could be produced by a large number of centrally located millisecond pulsars. The fact that no such pulsar population has been detected implies that these sources must be very faint and very numerous. Here, in this study, we use the contents of Fermi’s recently released Third Pulsar Catalog (3PC) to measure the luminosity function of the millisecond pulsars in the Milky Way’s disk. We find that this source population exhibits a luminosity function with a mean γ -ray luminosity of ⟨ L γ ⟩ ∼ 6 × 10 32 erg / s (integrated above 0.1 GeV). If the GCE were generated by millisecond pulsars with the same luminosity function, we find that ∼ 20 such sources from the inner Galaxy population should have already been detected by Fermi and included in the 3PC. Given the lack of such observed sources, we exclude the hypothesis that the GCE is generated by pulsars with the same luminosity function as those in the Galactic disk with a significance of 3.4 σ . We conclude that either less than 39% of the GCE is generated by pulsars, or that the millisecond pulsars in the inner Galaxy are at least 5 times less luminous on average than those found in the Galactic disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Photon asymmetry measurements of $\overrightarrow{\gamma}p \rightarrow \pi^{0} p$ γ → p → π 0 p for $E_{\gamma}=$ 320-650 MeV

High-statistics measurements of the photon asymmetry Σ for the $\overrightarrow{\gamma}p \rightarrow \pi^{0} p$ reaction have been made in the center-of-mass energy range W = 1214–1450 MeV. The data were measured with the MAMI A2 real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The resulting measurements significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. We have also combined the photon asymmetry results with recent cross-section measurements from Mainz to calculate the profile functions, $\check{Σ}$ (= σ 0 Σ), and perform a moment analysis. Comparison with calculations from the Bonn-Gatchina model shows that the precision of the data is good enough to further constrain the higher partial waves, and there is an indication of interference between the very small F-waves and the N(1520)3/2 - and N(1535)1/2 - resonances.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Meson Photo-Production in GEANT4 for $E_\gamma = 0.225$ E γ = 0 . 225 -3.0 GeV using the $\gamma + p \rightarrow p + \pi^{0}$ reaction

The study of nuclear resonances in the intermediate energy regime requires accurate modeling of the experimental physics background. The cross sections in the GEANT4 toolkit do not adequately treat meson photo-production. The purpose of this study is to compare experimental data and theoretical models implemented in version 9.6.p02 of the GEANT4 Monte Carlo simulation toolkit for the exclusive and differential cross sections of $\pi^0$ photo-production. Two models were studied: the Chiral Invariant Phase Space (CHIPS) and Bertini Cascade (BERT). The cross section data from the models were compared to the experimental data from the CEBAF Large Acceptance Spectrometer (CLAS) of Jefferson Lab and the phenomenological Scattering Analysis Interactive Dial-in (SAID) model. Relativistic Breit-Wigner fits were used to compare the $\Delta(1232)$, N*(1520), N*(1650) and N*(1875) resonances from SAID, CLAS and CHIPS, giving agreements to within 3% for the mass of each resonance. The limited tabulated data set of BERT does not allow for an accurate description of the energy distribution, even following its improvement in version 10p02. The angular distributions of the cross sections show significant differences between CHIPS and both CLAS and SAID data, the latter being the most accurate model to describe the $\gamma p\rightarrow p\pi ^0$ exclusive cross section. Finally, the physics in CHIPS appears to be correct but it needs further development for the individual resonances contributions that could be useful since it is also the only model able to treat electromagnetically induced meson production for $A>1$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗