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If dark matter has mass lower than around 1 GeV, it will not impart enough energy to cause detectable nuclear recoils in many direct-detection experiments. However, if dark matter is upscattered to high energy by collisions with cosmic rays, it may be detectable in both direct-detection experiments and neutrino experiments. We report the results of a dedicated search for boosted dark matter upscattered by cosmic rays using the PROSPECT reactor antineutrino experiment. We show that such a flux of upscattered dark matter would display characteristic diurnal sidereal modulation, and use this to set new experimental constraints on sub-GeV dark matter exhibiting large interaction cross-sections., 11 pages, 8 figures

The precision reactor oscillation and spectrum experiment, PROSPECT, has made world-leading measurements of reactor antineutrinos at short baselines. In its first phase, conducted at the high flux isotope reactor (HFIR) at Oak Ridge National Laboratory, PROSPECT produced some of the strongest limits on eV-scale sterile neutrinos, made a precision measurement of the reactor antineutrino spectrum from 235U, and demonstrated the observation of reactor antineutrinos in an aboveground detector with good energy resolution and well-controlled backgrounds. The PROSPECT collaboration is now preparing an upgraded detector, PROSPECT-II, to probe yet unexplored parameter space for sterile neutrinos and contribute to a full resolution of the reactor antineutrino anomaly, a longstanding puzzle in neutrino physics. By pressing forward on the world’s most precise measurement of the 235U antineutrino spectrum and measuring the absolute flux of antineutrinos from 235U, PROSPECT-II will sharpen a tool with potential value for basic neutrino science, nuclear data validation, and nuclear security applications. Following a two-year deployment at HFIR, an additional PROSPECT-II deployment at a low enriched uranium reactor could make complementary measurements of the neutrino yield from other fission isotopes. PROSPECT-II provides a unique opportunity to continue the study of reactor antineutrinos at short baselines, taking advantage of demonstrated elements of the original PROSPECT design and close access to a highly enriched uranium reactor core.

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of [Formula: see text] is important when making theoretical predictions. One source of [Formula: see text] that is often neglected arises from the irradiation of the nonfuel materials in reactors. The [Formula: see text] rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible [Formula: see text] sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the [Formula: see text] source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel [Formula: see text] contributions from HFIR to PROSPECT amount to 1% above the inverse beta decay threshold with a maximum contribution of 9% in the 1.8–2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel [Formula: see text] contribution.

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of ν ¯ e is important when making theoretical predictions. One source of ν ¯ e that is often neglected arises from the irradiation of the nonfuel materials in reactors. The ν ¯ e rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible ν ¯ e sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the ν ¯ e source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel ν ¯ e contributions from HFIR to PROSPECT amount to 1% above the inverse beta decay threshold with a maximum contribution of 9% in the 1.8-2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel ν ¯ e contribution.

The Precision Reactor Oscillation and Spectrum (PROSPECT) Experiment is a reactor neutrino experiment designed to search for sterile neutrinos with a mass on the order of 1 eV/c$^2$ and to measure the spectrum of electron antineutrinos from a highly-enriched $^{235}$U nuclear reactor. The PROSPECT detector consists of an 11 by 14 array of optical segments in $^{6}$Li-loaded liquid scintillator at the High Flux Isotope Reactor in Oak Ridge National Laboratory. Antineutrino events are identified via inverse beta decay and read out by photomultiplier tubes located at the ends of each segment. The detector response is characterized using a radioactive source calibration system. This paper describes the design, operation, and performance of the PROSPECT source calibration system.

This Letter reports the first measurement of the ^{235}U ν[over ¯]_{e} energy spectrum by PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, operating 7.9 m from the 85 MW_{th} highly enriched uranium (HEU) High Flux Isotope Reactor. With a surface-based, segmented detector, PROSPECT has observed 31678±304(stat) ν[over ¯]_{e}-induced inverse beta decays, the largest sample from HEU fission to date, 99% of which are attributed to ^{235}U. Despite broad agreement, comparison of the Huber ^{235}U model to the measured spectrum produces a χ^{2}/ndf=51.4/31, driven primarily by deviations in two localized energy regions. The measured ^{235}U spectrum shape is consistent with a deviation relative to prediction equal in size to that observed at low-enriched uranium power reactors in the ν[over ¯]_{e} energy region of 5-7 MeV.

This paper describes the design and performance of a 50 liter, two-segment $^{6}$Li-loaded liquid scintillator detector that was designed and operated as prototype for the PROSPECT (Precision Reactor Oscillation and Spectrum) Experiment. The two-segment detector was constructed according to the design specifications of the experiment. It features low-mass optical separators, an integrated source and optical calibration system, and materials that are compatible with the $^{6}$Li-doped scintillator developed by PROSPECT. We demonstrate a high light collection of 850$\pm$20 PE/MeV, an energy resolution of $\sigma$ = 4.0$\pm$0.2% at 1 MeV, and efficient pulse-shape discrimination of low $dE/dx$ (electronic recoil) and high $dE/dx$ (nuclear recoil) energy depositions. An effective scintillation attenuation length of 85$\pm$3 cm is measured in each segment. The 0.1% by mass concentration of $^{6}$Li in the scintillator results in a measured neutron capture time of $\tau$ = 42.8$\pm$0.2 $\mu s$. The long-term stability of the scintillator is also discussed. The detector response meets the criteria necessary for achieving the PROSPECT physics goals and demonstrates features that may find application in fast neutron detection., Comment: 16 pages, 13 figures; minor edits to design detail and references

This Letter reports the first scientific results from the observation of antineutrinos emitted by fission products of $^{235}$U at the High Flux Isotope Reactor. PROSPECT, the Precision Reactor Oscillation and Spectrum Experiment, consists of a segmented 4 ton $^6$Li-doped liquid scintillator detector covering a baseline range of 7-9 m from the reactor and operating under less than 1 meter water equivalent overburden. Data collected during 33 live-days of reactor operation at a nominal power of 85 MW yields a detection of 25461 $\pm$ 283 (stat.) inverse beta decays. Observation of reactor antineutrinos can be achieved in PROSPECT at 5$\sigma$ statistical significance within two hours of on-surface reactor-on data-taking. A reactor-model independent analysis of the inverse beta decay prompt energy spectrum as a function of baseline constrains significant portions of the previously allowed sterile neutrino oscillation parameter space at 95% confidence level and disfavors the best fit of the Reactor Antineutrino Anomaly at 2.2$\sigma$ confidence level., Comment: 7 pages, 5 figures; v3: Added additional supplemental files

The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, is designed to make both a precise measurement of the antineutrino spectrum from a highly-enriched uranium reactor and to probe eV-scale sterile neutrinos by searching for neutrino oscillations over meter-long baselines. PROSPECT utilizes a segmented $^6$Li-doped liquid scintillator detector for both efficient detection of reactor antineutrinos through the inverse beta decay reaction and excellent background discrimination. PROSPECT is a movable 4-ton antineutrino detector covering distances of 7m to 13m from the High Flux Isotope Reactor core. It will probe the best-fit point of the $\bar\nu_e$ disappearance experiments at 4$\sigma$ in 1 year and the favored regions of the sterile neutrino parameter space at more than 3$\sigma$ in 3 years. PROSPECT will test the origin of spectral deviations observed in recent $\theta_{13}$ experiments, search for sterile neutrinos, and address the hypothesis of sterile neutrinos as an explanation of the reactor anomaly. This paper describes the design, construction, and commissioning of PROSPECT and reports first data characterizing the performance of the PROSPECT antineutrino detector., Comment: 30 pages, 33 figures; updated with journal revision and reference

PROSPECT, the Precision Reactor Oscillation and SPECTrum experiment, is a short-baseline reactor antineutrino experiment designed to provide precision measurements of the $^{235}$U product $\overline{\nu}_e$ spectrum of utilizing an optically segmented 4-ton liquid scintillator detector. PROSPECT's segmentation system, the optical grid, plays a central role in reconstructing the position and energy of $\overline{\nu}_e$ interactions in the detector. This paper is the technical reference for this PROSPECT subsystem, describing its design, fabrication, quality assurance, transportation and assembly in detail. In addition, the dimensional, optical and mechanical characterizations of optical grid components and the assembled PROSPECT target are also presented. The technical information and characterizations detailed here will inform geometry-related inputs for PROSPECT physics analysis, and can guide a variety of future particle detection development efforts, such as those using optically reflecting materials or filament-based 3D printing., Comment: 31 pages, 28 figures

This work reports the production and characterization of lithium-loaded liquid scintillator (LiLS) for the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT). Fifty-nine 90 liter batches of LiLS (${}^6{\rm Li}$ mass fraction 0.082%$\pm$0.001%) were produced and samples from all batches were characterized by measuring their optical absorbance relative to air, light yield relative to a pure liquid scintillator reference, and pulse shape discrimination capability. Fifty-seven batches passed the quality assurance criteria and were used for the PROSPECT experiment., 16 pages, 15 figures

CdSe nanocrystals in solution and films can enter a metastable state in which the highly luminescent nanocrystals become dark. This change, which we attribute to a surface transformation, can be caused by heating or by changing the environment of the nanocrystals at room temperature. The metastable transformation is reversed upon illumination of above-band-gap light, at which point the nanocrystals are again highly luminescent.

Transmissivities were measured and absorption coefficients derived for three types of fused quartz between room temperature and 1500 degrees C: GE uv Type 151 (0.21-2.0 mu), GE ir Type 105 (0.21-3.5 mu), and Corning Vycor ir glass No. 7905 (1.7-4.0 mu). Less extensive measurements were also performed with Corning uv Type 7940. The interval of virtual transparency (transmissivity greater, similar0.85) of each type between the ultraviolet and near-infrared was reduced by heating due to a shift in both the long-and short-wavelength absorption edges.

The fundamental associated with the B–H and B—D stretching motions in HBBr2 and DBBr2 have been observed under high resolution. A series of evenly spaced lines occurs which has the appearance of a ⊥ band of a symmetric‐top molecule. Analysis of the spectra gives an approximate value for the smallest moment of inertia from which the apex angle Br–B–Br was calculated to be 119.3±2°. It was possible to assign K values to the individual lines and to determine the position of the band centers for both HBBr2 (2622.4 cm—1) and DBBr2 (1960.1 cm—1).

Using the Green’s function formulae for isotopic frequencies of the XY3 molecule together with the spectral theorem, explicit formulae for the molecular force constants directly in terms of the vibrational frequencies have been obtained. The relationship between the Wilson force constants and the cartesian force constants is discussed and leads to the above formulae. The procedure is applied to the BCl3 and BBr3 molecules and force constants are obtained. A simple procedure for calculating the variations in the force constants with variations in vibrational frequencies is suggested.

The vibrational frequencies of isotopically substituted planar XY3 molecules have been obtained using the Green's function and partitioning techniques. Taking HBCl2 as an ``isotopic'' species of BCl3, we have calculated its spectrum, without invoking a force constant model. The excellent agreement between predicted and observed spectra indicates that even the force constant changes may be neglected as a first approximation. Using the information provided by the calculations, we have observed and identified five of the six HBCl2 fundamentals: ν1 = 762 and 740 cm—1, 10B— and 11B–Cl symmetric stretches; ν2 = 2617 cm—1, B–H stretch (no splitting); ν4 = 1100 and 1089 cm—1, 10B— and 11B–Cl asymmetric stretch; ν5 = 892 cm—1 (11B only), in‐plane H deformation; and ν6 = 795 and 784 cm—1, out‐of‐plane deformation. Frequencies observed and identified for the deuterated compound are: ν2 = 1969 cm—1, B—D stretch; and ν6 = 661 and 645 cm—1, 10B–11B splitting. The calculations also indicate that the other frequencies we have not observed are hidden by BCl3 bands, and that ν3, a B–Cl bending mode is, at ≈285–290 cm—1, outside the range of our instrument.

The vibrational spectrum of the ``perturbed'' molecules H11BBr2, H10BBr2, D11BBr2, and D10BBr2 were generated from the Green's function of the ``unperturbed'' boron tribromides 11BBr3 and 10BBr3. Effect of geometry changes imposed by replacing a halogen by hydrogen on the B1 modes has been calculated and the results indicate a strong dependence on the BH and BD bond length. Using information provided by the calculations, we have observed and identified five of the six HBBr2 and DBBr2 fundamentals. The bands are reported in the following order (cm−1): H11BBr2, D11BBr2, and D10BBr2: ν1 (BBr symmetric stretch), 595, ___, 585, ___; ν2 (BH and BD stretch), 2622, 2622, 1960, ___; ν3 (BBr symmetric deformation), ≈180–190 cm−1, calculated values only; ν4 (BBr asymmetric stretch), 1036, 1048, 870, 901; ν5 (BH and BD in‐plane deformation), 772, ___, 656, ___; ν6 (out‐of‐plane deformation), 731, ___, 625?, ___. Blanks refer to unobserved bands. The calculated in‐plane frequencies have been brought into alignment wit...

The ν2 fundamental of HBCl2 and DBCl2 has been observed under high resolution. A series of evenly spaced lines occurs, which has the appearance of a ⊥ band of a symmetric top molecule. Analysis of the spectra gives an approximate value for the smallest moment of inertia, from which the following molecular dimensions are calculated: B–H bond length=1.13±0.2 A and Cl–B–Cl bond angle=119.7±3°. The position of the band center, 2616.9 cm—1, for HBCl2, has also been determined.

Four HBF2 and two DBF2 fundamentals have been resolved into their fine structure under medium dispersion. The three A1 modes, v1, v2, and v3 are characterized by a series of evenly spaced lines having the general appearance of a ⊥ band of a symmetric‐top molecule. The B2 modes, v6, have a strong Q branch in addition to a well‐defined subband system and have the appearance of Type‐C bands near the prolate limit. Using a symmetric‐top approximation, an analysis of the spectra provided six independent measurements for the smallest moment of inertia from which the average apex angle F–B–F was calculated to be 117.4±2° assuming the BH(BD) bond distance to be 1.20 A. In HBF2, interband agreement of the rotational constant A, associated with the smallest moment of inertia, was quite good. It was possible to assign K values to the individual lines and to determine the position of the band centers for the resolvable fundamentals v1, v2, v3, and v6.

A chromium wire‐grid duplexer polarizer for CO2 lasers has been developed using holographic and chemical etching techniques. The reflection and transmission measurements show reasonably good agreement with the theory.

The Air Force Materials Laboratory has conducted an internal test program to obtain design information on titanium alloy castings to facilitate a wider usage of this material where its application will benefit Air Force Systems. Emphasis was on obtaining room and elevated temperature fatigue data on the Ti-6Al-4V alloy in the annealed and heat-treated conditions. Limited fracture toughness, stress rupture and creep data were also obtained. The results showed generally favorable properties compared to forgings, plate and extrusions of the same alloy; however, existing production and inspection techniques do not always insure a flaw-free product.Copyright © 1969 by ASME

Transmissivities were measured and absorption coefficients derived for three types of fused quartz between room temperature and 1500 degrees C: GE uv Type 151 (0.21-2.0 mu), GE ir Type 105 (0.21-3.5 mu), and Corning Vycor ir glass No. 7905 (1.7-4.0 mu). Less extensive measurements were also performed with Corning uv Type 7940. The interval of virtual transparency (transmissivity greater, similar0.85) of each type between the ultraviolet and near-infrared was reduced by heating due to a shift in both the long-and short-wavelength absorption edges.