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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Signatures of muonic activation in the Majorana Demonstrator

Experiments searching for very rare processes such as neutrinoless double-beta decay require a detailed understanding of all sources of background. Signals from radioactive impurities present in construction and detector materials can be suppressed using a number of well-understood techniques. Background from in situ cosmogenic interactions can be reduced by siting an experiment deep underground. However, the next generation of such experiments have unprecedented sensitivity goals of 10 28 years half-life with background rates of 10 -5 cts/(keV kg yr) in the region of interest. To achieve these goals, the remaining cosmogenic background must be well understood. In the work presented here, Majorana Demonstrator data are used to search for decay signatures of metastable germanium isotopes. Contributions to the region of interest in energy and time are estimated using simulations and compared to Demonstrator data. Correlated time-delayed signals are used to identify decay signatures of isotopes produced in the germanium detectors. A good agreement between expected and measured rate is found and different simulation frameworks are used to estimate the uncertainties of the predictions. The simulation campaign is then extended to characterize the background for the LEGEND experiment, a proposed tonne-scale effort searching for neutrinoless double-beta decay in 76 Ge .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

First β -delayed neutron spectroscopy of 24 O

The β decay of 24 O was investigated at NSCL/MSU using a combination of neutron and γ-ray spectroscopy. For the first time, the β-delayed neutron energy spectrum of 24 O was measured, revealing three intensely populated, isolated neutron-unbound states in 24 F. This allowed for the extraction of the decay strength in 24 F up to 6.2 MeV. A comprehensive comparison of the experimental results with various nuclear theories, ranging from the empirical shell model to the most advanced ab initio calculations, was conducted. While most theoretical predictions align with the experimental data for low-lying states, discrepancies arise at higher excitation energies. Finally, in the transition from 24 O to 24 F, shell model calculations using the empirical USDB interaction predicted the structure of both nuclei without invoking the need for a stronger proton-neutron tensor force, which was postulated for the neighboring isotone 25 F.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Signal processing and spectral modeling for the BeEST experiment

The Beryllium Electron capture in Superconducting Tunnel junctions (BeEST) experiment searches for evidence of heavy neutrino mass eigenstates in the nuclear electron capture decay of 7 Be by precisely measuring the recoil energy of the 7 Li daughter. In Phase III, the BeEST experiment has been scaled from a singl superconducting tunnel junction (STJ) sensor to a 36-pixel array to increase sensitivity and mitigate gamma-induced backgrounds. Phase III also uses a new continuous data acquisition system that greatly increases the flexibility for signal processing and data cleaning. Here, we have developed procedures for signal processing and spectral fitting that are sufficiently robust to be automated for large datasets. Furthermore, this article presents the optimized procedures before unblinding the majority of the Phase III dataset to search for physics beyond the standard model.

6 ≤ A ≤ 19↗
DOE OSTI2024

Exotic Dark Matter Search with the Majorana Demonstrator

With excellent energy resolution and ultralow-level radiogenic backgrounds, the high-purity germanium detectors in the enable searches for several classes of exotic dark matter (DM) models. In this work, we report new experimental limits on keV-scale sterile neutrino DM via the transition magnetic moment from conversion to active neutrinos ν s → ν a . We report new limits on fermionic dark matter absorption ( χ + A → ν + A ) and sub-GeV DM-nucleus 3 → 2 scattering ( χ + χ + A → ϕ + A ), and new exclusion limits for bosonic dark matter (axionlike particles and dark photons). These searches utilize the (1–100)-keV low-energy region of a 37.5-kg y exposure collected by the between May 2016 and November 2019 using a set of Ge 76 -enriched detectors whose surface exposure time was carefully controlled, resulting in extremely low levels of cosmogenic activation. Published by the American Physical Society 2024

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Investigation of the damping wiggler effect and application on the PAL fourth-generation storage ring

An investigation of the damping wiggler effect to reduce the emittance in the Pohang Accelerator Laboratory (PAL), a fourth-generation storage ring (4GSR) that uses a multi-bend achromat, is presented. Furthermore, a 4GSR lattice which has reduced emittance and increased dynamic aperture to amplify the synergy with two existing light sources (PLS-II and PAL-XFEL) at PAL is described.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Seeing through nuclear fuel: Three-dimensional, nondestructive X-ray microscopy and volumetric analyses of neutron-irradiated TRISO-coated fuel kernels

The three-dimensional (3D) characterization of nuclear fuel with X-ray microscopy has historically proven difficult, due to uranium’s high attenuation of easily accessible X-rays, both in a laboratory setting and at a synchrotron user facility. However, this imaging modality provides nondestructive information that can be used to investigate morphological changes arising from external stimuli (e.g., neutron irradiation, high-temperature testing). Using an appropriate X-ray energy spectrum and an adequate X-ray filter, suitable transmissions through properly sized nuclear fuel specimens can be achieved. Here, in this study, we present the methods and results of using a commercially available, laboratory-based X-ray microscope (XRM) to examine the extent of 3D morphological changes of tristructural isotropic (TRISO)-coated fuel particles, specifically uranium oxide/uranium carbide fuel kernels, after high-temperature neutron irradiation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Demonstration of a new unstructured mesh IMC x-ray transport capability in LAP codes

In this document, the Advanced Simulation and Computing (ASC) Transport Project’s Jayenne team presents evidence that the Los Alamos National Laboratory (LANL) Level 2 milestone statement, Demonstrate a new unstructured mesh IMC x-ray transport capability in LAP codes, due Q4 FY20, has been satisfied with the release and integration of the Jayenne team’s Implicit Monte Carlo (IMC) solver libraries into the lumos multiphysics solver. The Jayenne project’s software includes the algorithms and features prescribed by the milestone description. The lumos software is maintained by the Lagrangian Applications Project (LAP) along with the hydrodynamics code flag and operates under the same ASC program as Jayenne. A set of demonstration problems has been specified, executed, and analyzed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Development of selenium imaging detectors toward a definitive search for neutrinoless ββ decay

Imaging sensors made from an ionization target layer of amorphous selenium (aSe) coupled to a silicon complementary metal-oxide-semiconductor (CMOS) active pixel array for charge readout are a promising technology for neutrino physics. The high spatial resolution in a solid-state target provides unparalleled rejection of backgrounds from natural radioactivity in the search for the neutrinoless ββ decay of 82 Se. With this grant, we experimentally determined two crucial factors necessary for the realization of this novel technology: i) the intrinsic energy response of aSe to ionizing electrons, and ii) the feasibility to couple a target layer of aSe to a CMOS active pixel sensor to image electron tracks.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Availability of Shielding Benchmark Experiment Data in the ICSBEP Handbook

The International Criticality Safety Benchmark Evaluation Projects (ICSBEP) has over two decades of experience under the auspices of the Organisation for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA) to identify, evaluate, and compile a comprehensive data set of criticality safety benchmark data [1]. The activities of the ICSBEP have led to the continued success of the International Handbook of Evaluated Criticality Safety Benchmark Experiments (ICSBEP Handbook) [2]. The contents of the ICSBEP Handbook include benchmark specifications derived from nuclear facilities around the world, which have been utilized to support criticality safety efforts and also integral testing of nuclear data [3]. The 2020 edition of the ICSBEP Handbook will include data from 582 evaluations containing benchmark specifications for 5,053 critical, subcritical, or near-critical configurations. There are seven criticality-alarm-placement/shielding evaluations containing a total of 45 benchmark configurations, and ten fundamental physics evaluations containing a total of 237 measurements relevant to criticality safety applications. The purpose of this paper is to summarize those benchmarks relative to validation needs in shielding applications currently found within the ICSBEP Handbook. The current and future plans of shielding benchmarks with regards to the ICSBEP will also be discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

A phase-field model for void and gas bubble superlattice formation in irradiated solids

A phase-field model to simulate the formation of both void and gas bubble superlattices is derived from a grand potential functional, assuming 1D diffusion of self-interstitial atoms. The model is capable of accounting for superlattice formation by either a nucleation and growth or spinodal decomposition mechanism; in this work, we focus on the nucleation and growth mechanism, using a discrete nucleation approach in the phase-field model. In simulations of void formation, short aligned rows of voids were initially formed, followed by growth in the size of the aligned rows, and finally leading to superlattice formation, consistent with experimental observations. Void superlattice spacing as a function of model parameters was quantified. Increased nucleation rates led to smaller superlattice spacing, while increased vacancy diffusivity led to larger superlattice spacing. In simulations of gas bubble superlattice formation, superlattice spacing decreased with increasing gas atom flux, consistent with experimental observations. Here, simulations with increasing ratio of gas atom flux to vacancy-interstitial pair production led to increased superlattice spacing, which is inconsistent with experimental observations at high gas atom flux rates; this discrepancy is attributed to the fact that the model does not account for bound gas atom-vacancy pairs that may dominate at high gas flux rates.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Measurements and models of enhanced recombination following inner-shell vacancies in liquid xenon

Electron-capture decays of 125 Xe and 127 Xe , and double-electron-capture decays of 124 Xe , are backgrounds in searches for weakly interacting massive particles (WIMPs) conducted by dual-phase xenon time projection chambers such as LUX-ZEPLIN (LZ). These decays produce signals with more light and less charge than equivalent-energy 𝛽 decays and correspondingly overlap more with WIMP signals. We measure three electron-capture charge yields in LZ: the 1.1 keV M-shell, 5.2 keV L-shell, and 33.2 keV K-shell at drift fields of 193 and 96.5 V/cm. The LL double-electron-capture decay of 124 Xe exhibits even more pronounced shifts in charge and light. We provide a first model of double-electron-capture charge yields using the link between ionization density and electron-ion recombination, and identify a need for more accurate calculations. Finally, we discuss the implications of the reduced charge yield of these decays and other interactions creating inner-shell vacancies for future dark matter searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Measurement of the Li 7 ( γ , t ) He 4 ground-state cross section between E γ = 4.4 and 10 MeV

Here, the Li 7 ( γ , t ) He 4 ground state cross section was measured for the first time using monoenergetic γ rays with energies between 4.4 and 10 MeV at the High Intensity Gamma-ray Source. The reaction is important for the primordial Li problem and for testing our understanding of the mirror α -capture reactions H 3 ( α , γ ) Li 7 and He 3 ( α , γ ) Be 7 . Although over the last 30 years most measurements of the H 3 ( α , γ ) Li 7 reaction have concentrated in an energy range below E γ = 3.65 MeV, measurements at higher energies could potentially restrict the extrapolation to astrophysically important energies. The experimental arrangement for measuring the Li 7 ( γ , t ) He 4 reaction included a large-area silicon detector array and several beam characterization instruments. The experimental astrophysical S factor of H 3 ( α , γ ) calculated from the present data was fitted using the R -matrix formalism. The results are in disagreement with previous experimental measurements in the same energy range but the extrapolated S factor agrees with the potential model calculation and lower energy experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Measurements of proton capture in the A=100–110 mass region: Constraints on the In 111 (γ,p)/(γ,n) branching point relevant to the γ process

The γ process is an explosive astrophysical scenario, which is thought to be the primary source of the rare proton-rich stable p nuclei. However, current γ-process models remain insufficient in describing the observed p-nuclei abundances, with disagreements up to two orders of magnitude. A sensitivity study has identified 111 In as a model-sensitive (γ,p)/(γ,n) branching point within the γ process. Constraining the involved reaction rates may have a significant impact on the predicted p-nuclei abundances. Here we report on measurements of the cross sections for 102 Pd (p,γ) 103 Ag, 108 Cd (p,γ) 109 In, and 110 Cd (p,γ) 111 In reactions for proton laboratory energies 3–8 MeV using the high efficiency total absorption spectrometer and the γ-summing technique. These measurements were used to constrain Hauser-Feshbach parameters used in talys 1.9, which constrains the 111 In(γ,p) 110 Cd and 111 In(γ,n) 110 Ag reaction rates. The newly constrained reaction rates indicate that the 111 In(γ,p)/(γ,n) branching point occurs at a temperature of 2.71 ± 0.05 GK, well within the temperature range relevant to the γ process. These findings differ significantly from previous studies and may impact the calculated abundances.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

New measurement of the E c.m . = 323 keV resonance in the 19 F(p,γ) 20 Ne reaction

At temperatures below 0.1 GK, the 19 F(p, γ) 20 Ne reaction is the only breakout path out of the CNO cycle. Experimental studies of this reaction are challenging from a technical perspective due to copious γ -ray background from the far stronger 19 F(p, α) 16 O reaction channel. Here, we present the first inverse kinematics study of the 19 F(p, γ) 20 Ne reaction, in which we measure the strength of the 323-keV resonance. We find a strength value of ωγ = $3.3$$^{+1.1}_{–0.9}$ meV, which is a factor of two larger than the most recent previous study. Here, the discrepancy is likely the result of a direct to ground state transition which previous studies were not sensitive to. We also observe the transition to the first 2 – state, which has not been observed for this resonance in previous studies. A new thermonuclear reaction rate is calculated and compared with the literature.

20 ≤ A ≤ 38↗
DOE OSTI2024

Strength measurement of the $E^{lab}_α = 830$ keV resonance in the 22 Ne (α,n) 25 Mg reaction using a stilbene detector

The interplay between the 22 Ne (α,γ) 26 Mg reaction and the competing 22 Ne ⁢(α,n) 25 Mg reaction determines the efficiency of the latter as a neutron source at the temperatures of stellar helium burning. In both cases, the rates are dominated by the α-cluster resonance at 830 keV. This resonance plays a particularly important role in determining the strength of the neutron flux for both the weak and main s process as well as the n process. Recent experimental studies based on transfer reactions suggest that the neutron and γ-ray strengths for this resonance are approximately equal. In this study, the 22 Ne (α,n) 25 Mg resonance strength has been remeasured and found to be similar to the previous direct studies. Finally, this reinforces an 830 keV resonance strength that is approximately a factor of 3 larger for the 22 Ne ⁢(α,n) 25 Mg reaction than for the 22 Ne (α,γ) 26 Mg reaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Development of Fast Decay-Energy Spectroscopy With Magnetic Microcalorimeters

Decay energy spectroscopy (DES) is an increasingly important radiometric technique arising from the unique thermal detection physics and the precision of low-temperature microcalorimetry. DES can enable high-precision analysis of very small amounts of radioactive material with simple and rapid sample preparation, making it a key new tool for nuclear safeguards, nuclear forensics, the improvement of nuclear data, measurements of absolute activity, and other applications. For problems in nuclear safeguards and nuclear forensics it is highly desirable to increase the count rates achievable in DES, while maintaining simple and rapid sample preparation. Here, in this report, we describe progress in a new project to achieve high count rates in DES by taking advantage of the physics of magnetic microcalorimetry. We describe the results of initial modeling and experiment to validate the idea, a sample fabrication technique suitable for nuclear materials laboratories, the preparation and initial tests of paramagnetic Au-Er alloy in thin foil form, and the development of a sensing coil geometry that will perform well with the increased-thickness sensor used in the new technique.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗