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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Diffuse boosted cosmic neutrino background

Energetic cosmic rays scatter off the cosmic neutrino background throughout the history of the Universe, yielding a diffuse flux of cosmic relic neutrinos boosted to high energies. We calculate this flux under different assumptions of the cosmic-ray flux spectral slope and redshift evolution. The nonobservation of the diffuse flux of boosted relic neutrinos with current high-energy neutrino experiments already excludes an average cosmic neutrino background overdensity larger than ∼10 4 over cosmological distances. We discuss the future detectability of the diffuse flux of boosted relic neutrinos in light of neutrino overdensity estimates and cosmogenic neutrino backgrounds.

Astronomy & Astrophysics↗
DOE OSTI2026

Charge-trap analysis in a SENSEI skipper-CCD: Understanding low-energy backgrounds in rare-event searches

Skipper charge-coupled devices (CCDs) are ultralow-threshold detectors capable of detecting energy deposits in silicon at the electronvolt scale. Skipper CCDs are increasingly used in rare-event searches, including experiments such as SENSEI, DAMIC-M, Oscura, and CONNIE, where one of the major challenges is mitigating low-energy backgrounds. In this work, we present results on trap characterization in a silicon skipper-CCD produced in the same fabrication run as the SENSEI experiment at SNOLAB. Lattice defects contribute to backgrounds in rare-event searches through single-electron charge trapping. To investigate this, we use the charge-pumping technique at different temperatures to identify dipoles produced by traps in the CCD channel. We fully characterize a fraction of these traps and use this information to extrapolate their contribution to the single-electron background in SENSEI. We find that this subpopulation of traps does not contribute significantly, but more work is needed to assess the impact of the traps that cannot be characterized.

Brusco, Agustin↗
DOE OSTI2024

Cherenkov photon background for low-noise silicon detectors in space

Future space observatories dedicated to direct imaging and spectroscopy of extra-solar planets will require ultra-low-noise detectors that are sensitive over a broad range of wavelengths. Silicon charge-coupled devices (CCDs), such as EMCCDs, Skipper CCDs, and Multi-Amplifier Sensing CCDs, have demonstrated the ability to detect and measure single photons from ultra-violet to near-infrared wavelengths, making them candidate technologies for this application. In this context, we study a relatively unexplored source of low-energy background coming from Cherenkov radiation produced by energetic charged particles traversing a silicon detector. In the intense radiation environment of space, energetic cosmic rays produce high-energy tracks and more extended halos of low-energy Cherenkov photons, which are detectable with ultra-low-noise detectors. We present a model of this effect that is calibrated to laboratory data, and we use this model to characterize the residual background rate for ultra-low noise silicon detectors in space. We find that the rate of cosmic-ray-induced Cherenkov photon production is comparable to other detector and astrophysical backgrounds that have previously been considered.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

RAIS Paducah Background Values

The Paducah Background Values (https://rais.ornl.gov/tools/pgdp_background.html) are from Methods for Conducting Risk Assessments and Risk Evaluations at the Paducah Gaseous Diffusion Plant, Volume 1, Human Health, which sought to establish provisional background values for groundwater and soil. These values were developed by considering agreements reached between the DOE and the regulatory agencies during comment resolution meetings, in the Federal Facility Agreement, and at technical meetings. The Paducah background concentrations are available for soil (surface and subsurface) and groundwater (filtered and unfiltered).

Dolislager, Fred [Oak Ridge National Laboratory (O↗
DOE OSTI2024

Developing a data-driven method to constrain the antiproton background in the Mu2e experiment

The Mu2e experiment will search for CLFV neutrinoless coherent muon to electron conversion in the field of an Al nucleus. The expected signal is a 104.97 MeV/c monochromatic $e^-$ (CE). CE-like $e^-$’s could also come from $\bar{p}$’s annihilating in the Stopping Target (ST). The background induced by $\bar{p}$’s is expected to be low but has a large systematic uncertainty. It cannot be suppressed by the time window cut used to reduce the prompt background. However, $p\bar{p}$ annihilation in the ST is the only source of events in the Mu2e detector with multiple tracks coming from the ST, simultaneous in time, each with a momentum in the signal window region. We exploited this unique feature and developed algorithms to identify and reconstruct multi-track events. This paper discusses the status and prospects of this data-driven method to constrain the $\bar{p}$ background at Mu2e.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Background Measurements and Simulations of the ComPair Balloon Flight

ComPair, a prototype of the All-sky Medium Energy Gamma-ray Observatory (AMEGO), completed a short-duration high-altitude balloon campaign on 27 August 2023 from Fort Sumner, New Mexico, USA. The goal of the balloon flight was to demonstrate ComPair as both a Compton and Pair telescope in flight, reject the charged particle background, and measure the background γ-ray spectrum. This analysis compares measurements from the balloon flight with Monte Carlo simulations to benchmark the instrument. The comparison finds good agreement between the measurements and simulations and supports the conclusion that ComPair accomplished its goals for the balloon campaign. Additionally, two charged particle background rejection schemes are discussed: a soft ACD veto that records a higher charged particle event rate but with less risk of event loss, and a hard ACD veto that limits the charged particle event rate on board. There was little difference in the measured spectra from the soft and hard ACD veto schemes, indicating that the hard ACD veto could be used for future flights. The successes of ComPair’s engineering flight will inform the development of the next generation of ComPair with upgraded detector technology and larger active area.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Neural Posterior Estimation for Cataloging Astronomical Images with Spatially Varying Backgrounds and Point Spread Functions

Neural posterior estimation (NPE), a type of amortized variational inference, is a computationally efficient means of constructing probabilistic catalogs of light sources from astronomical images. To date, NPE has not been used to perform inference in models with spatially varying covariates. However, ground-based astronomical images exhibit spatially varying sky backgrounds and point spread functions (PSFs), and accounting for this variation is essential for constructing accurate catalogs of imaged light sources. In this work, we introduce a novel NPE-based cataloging method that trains an inference network with semisynthetic astronomical images generated using PSFs and backgrounds sampled from the Sloan Digital Sky Survey. In experiments with semisynthetic images, we evaluate the method on key cataloging tasks: light source detection, star/galaxy separation, and flux measurement. A “generalist” inference network—trained with diverse PSFs and backgrounds—performs as well as a “specialist” network even when both are evaluated on the specialist’s particular PSF/background combination. This result suggests that a single NPE network can generalize across spatial variations, eliminating the need for retraining on each observational condition.

astronomy image processing↗
DOE OSTI2026

Data-driven Techniques for $v^{e}$ Signal and Background Predictions in NOνA

NOν \nu A is a long baseline neutrino oscillation experiment, using two functionally identical detectors to measure νe \nu_e appearance and νμ \nu_\mu disappearance at the Far Detector (FD) with the NuMI Beam at Fermilab. The Near Detector (ND) measures the beam before oscillations, which will allow us to make a measurement of the signal flux before it has oscillated and the background components which can mimic νe \nu_e at our FD. We use the ND in three different ways to predict the amount of signal and background expected at the FD to partially cancel systematic uncertainties. The background prediction has three components: Charged Current (CC) νμ \nu_\mu , νe \nu_e and Neutral Current (NC) events. We need to determine the fraction of the selected ND sample in each of these components because some oscillate significantly (CC νμ \nu_\mu ) and some do not oscillate at all (NC). This poster will present details of these three data-driven techniques for predicting the FD spectrum.

Yu, Shiqi [Argonne; IIT, Chicago]↗
NASA NTRS1972

Signal sequence detection given noisy, common background image sets.

The optimum processing (likelihood functional) is found for a set of M images, each the sum of a member of a signal sequence due to an object to be detected and its parameters estimated, a sample function of a noise field, and a sample function of a common background field. The noise fields are independent, zero mean, white Gaussian fields, all independent of the background field. The latter is assumed to be either (1) completely unknown or of known mean and covariance functions with (2) a certain fluctuation property or (3) Gaussian. Three equivalent forms of the optimum processing are found: (1) a summation of generalized matched filterings of the images, (2) a summation of matched filtering of certain generalized differences of the images, and (3) a summation of 'estimator-correlator' type filterings. The detection performance and optimum signal/image selection under the Neyman-Pearson criterion is given, and is shown that optimum processor and signal design can completely eliminate any effect of the background on detectability.

Harger, R. O.↗
NASA NTRS1972

Momentum transfer interaction of a laser-produced plasma with a low-pressure background.

The expansion of a laser-produced metallic plasma into a photoionized hydrogen background has been experimentally studied. Langmuir probe and microwave diagnostics have detected an interaction front which decelerates with a dependence on background density and time consistent with a momentum coupling between the laser plasma and the ionized fraction of the background. An ion percursor has also been observed. Calculations of scattering cross sections indicate that multiple-encounter Coulomb scattering will dominate collisional momentum transfer. The leading edge of the laser plasma contains multiply charged ions of charge state z greater than or equal to 5, and collisional effects appear adequate to explain the principal features of the momentum coupling. The ion precursor may have a collisionless origin.

Koopman, D. W.↗
NASA NTRS1974

The origin of the diffuse background gamma-radiation

Recent observations have now provided evidence for diffuse background gamma radiation extending to energies beyond 100 MeV. There is some evidence of isotropy and implied cosmological origin. Significant features in the spectrum of this background radiation have been observed which provide evidence for its origin in nuclear processes in the early stages of the big-band cosmology and tie in these processes with galaxy fromation theory. A crucial test of the theory may lie in future observations of the background radiation in the 100 MeV to 100 GeV energy range which may be made with large orbiting spark-chamber satellite detectors. A discussion of the theoretical interpretations of present data, their connection with baryon symmetric cosmology and galaxy formation theory, and the need for future observations are given.

Stecker, F. W.↗
NASA NTRS1974

On the possibility of a geocoronal contribution to the celestial soft X-ray background

The possibility is investigated that a significant fraction of the X-ray background in the energy range from 0.2 to 0.28 keV originates in the geocorona through bremsstrahlung. It is concluded that the geocoronal flux must be substantial at some times and the possibility exists that an observable geocoronal background exists at all times. The existing data on the soft X-ray background is found to be compatible with the hypothesis of a geocoronal component.

Mack, J. E.↗
NASA NTRS1975

Background estimation in a (gnu e)-diffusion detector

Background conditions for detecting (gamma e)-diffusion are discussed with reference to the utilization of a hodoscope system consisting of wide area flat Geiger counters connected for coincidence and of a controllable spark chamber. When calculating the background, any organic compounds synthesized from C, O2 and H2 with radioactive admixtures is presumed to be the preferrable material for the construction of the detector. The number of background events simulating the effect sought is estimated by analyzing the spectrum of the organic glass gamma radiation caused by disintegration and fission of long lived isotopes and by nuclear reactions with the participation of alpha particles and neutrons.

Glotov, V. I.↗
NASA NTRS1974

The origin of the diffuse background gamma radiation

Recent observations provided evidence for diffuse background gamma radiation extending to energies beyond 100 MeV, and evidence of isotropy and implied cosmological origin. Significant features in the spectrum of this background radiation were observed which provide evidence for its origin in nuclear processes in the early stages of big-bang cosmology, and connect these processes with the galaxy formation theory. A test of the theory is in future observations of the background radiation in the 100 MeK to 100 GeV energy range which are made with large orbiting spark-chamber satellite detectors. The theoretical interpretations of present data, their connection with baryon-symmetric cosmology and galaxy formation theory, and the need for future observations are discussed.

Stecker, F. W.↗
NASA NTRS1976

On the ultrasoft X-ray background

The soft X-ray background has been studied down to energies of the order of 90 eV. The spectrum is found to be extremely soft, though not as steeply rising toward very low energies as indicated by Yentis et al. (1972). The background is both softer and more intense at high northern galactic latitudes than at low latitudes. Measured pulse-height spectra are analyzed under the assumption of different source models. The results are consistent with an origin of the background in a hot interstellar plasma with a temperature of about 800,000 K and a hot electron density of approximately 0.001 per cu cm. Upper limits are set on the soft X-ray emission from several interesting stellar objects.

Levine, A.↗
NASA NTRS1977

High-resolution observations of the Lyman alpha sky background

The first high-resolution observations of the Lyman alpha sky background, obtained with a spectrometer on the Copernicus satellite, are examined. The high-resolution observations presented allow the first direct measurement of the heliocentric velocity of the local interstellar medium. The high resolution of the spectrometer and the projection of the earth's orbital velocity along the line of sight made it possible to separate the weak extraterrestrial background feature from the intense geocoronal emission line. The observations also contain considerable information about the Lyman alpha emission from the geocorona. The data permit limits to be placed on the temperature of the gas that produces the background feature.

Adams, T. F.↗
NASA NTRS1977

Distinguishing vegetation from soil background information

In aircraft and satellite multispectral scanner data, soil background signals are superimposed on or intermingled with information about vegetation. A procedure which accounts for soil background would, therefore, make a considerable contribution to an operational use of Landsat and other spectral data for monitoring the productivity of range, forest, and crop lands. A description is presented of an investigation which was conducted to obtain information for the development of such a procedure. The investigation included a study of the soil reflectance that supplies the background signal of vegetated surfaces. Landsat data as recorded on computer compatible tapes were used in the study. The results of the investigation are discussed, taking into account a study reported by Kauth and Thomas (1976). Attention is given to the determination of Kauth's plane of soils, sun angle effects, vegetation index modeling, and the evaluation of vegetation indexes. Graphs are presented which show the results obtained with a gray mapping technique. The technique makes it possible to display plant, soil, water, and cloud conditions for any Landsat overpass.

Richardson, A. J.↗
NASA NTRS1977

Neutral particle background in cosmic ray telescopes composed of silicon solid state detectors

The energy loss-spectrum of secondary charged particles produced by the interaction of gamma-rays and energetic neutrons in silicon solid state detectors has been measured with a satellite-borne cosmic ray telescope. In the satellite measurements presented here two distinct neutral background effects are identified: secondary protons and alpha particles with energies of about 2 to 100 MeV produced by neutron interactions, and secondary electrons with energies of about 0.2 to 10 MeV produced by X-ray interactions. The implications of this neutral background for satellite measurements of low energy cosmic rays are discussed, and suggestions are given for applying these results to other detector systems in order to estimate background contamination and optimize detector system design.

Mewaldt, R. A.↗