Nuclear reactors are uniquely powerful, abundant, and flavor-pure sources of antineutrinos that continue to play a vital role in the US neutrino physics program. The US reactor antineutrino physics ...community is a diverse interest group encompassing many detection technologies and many particle physics topics, including Standard Model and short-baseline oscillations, BSM physics searches, and reactor flux and spectrum modeling. The community's aims offer strong complimentary with numerous aspects of the wider US neutrino program and have direct relevance to most of the topical sub-groups composing the Snowmass 2021 Neutrino Frontier. Reactor neutrino experiments also have a direct societal impact and have become a strong workforce and technology development pipeline for DOE National Laboratories and universities. This white paper, prepared as a submission to the Snowmass 2021 community organizing exercise, will survey the state of the reactor antineutrino physics field and summarize the ways in which current and future reactor antineutrino experiments can play a critical role in advancing the field of particle physics in the next decade.
This Letter reports one of the most precise measurements to date of the antineutrino spectrum from a purely ^{235}U-fueled reactor, made with the final dataset from the PROSPECT-I detector at the ...High Flux Isotope Reactor. By extracting information from previously unused detector segments, this analysis effectively doubles the statistics of the previous PROSPECT measurement. The reconstructed energy spectrum is unfolded into antineutrino energy and compared with both the Huber-Mueller model and a spectrum from a commercial reactor burning multiple fuel isotopes. A local excess over the model is observed in the 5-7 MeV energy region. Comparison of the PROSPECT results with those from commercial reactors provides new constraints on the origin of this excess, disfavoring at 2.0 and 3.7 standard deviations the hypotheses that antineutrinos from ^{235}U are solely responsible and noncontributors to the excess observed at commercial reactors, respectively.
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We present a summary of initial work on the etching of silica at 157 nm. At fluences well below the threshold for plasma formation, we have characterized the direct desorption of atomic ions from ...fused silica surfaces during 157-nm irradiation. The ion identities and kinetic energies were determined by time-resolved mass spectroscopy. The principal ions are Si+ and O+. The emission intensities are dramatically increased by treatments that are expected to increase the density of surfaces defects. Molecular dynamics simulations of the silica surface suggest that silicon ions bound at surface oxygen vacancies (analogous to E' centers) provide suitable configurations for emission. We propose that emission is best understood in terms of a hybrid mechanism involving both antibonding chemical forces (Menzel-Gomer-Redhead model) and repulsive electrostatic forces on the adsorbed ion after laser excitation of the underlying defect.
We report measurements of laser-induced photoelectron emission (LIPEE) from single crystal aluminum (99.999%) and high purity polycrystalline aluminum (>99.9%) during uniaxial tensile deformation. A ...248-nm excimer laser (5-eV photon energy) was used as a light source. Deformation was performed on a tensile stage in ultra-high vacuum at an initial strain rate of 1 × 10−3 s−1. Photoelectron intensities are sensitive to changes in surface morphology accompanying deformation, including slip line and band formation. In the single crystal material, LIPEE intensity initially increases linearly with strain followed by a monotonically decreasing slope at larger strain. In the polycrystalline material, LIPEE intensities increase linearly with strain in two segments. Slip bands on the deformed surfaces were characterized by atomic force microscopy (AFM).
We report scanning force microscope (SFM) observations of enhanced calcite dissolution in aqueous solution due to mechanical stimulation induced by the SFM tip. Images and mechanical treatment were ...performed in saturated (≥60 μM) CaCO3 solution adjusted to pH ∼9. Small area scans of monolayer steps significantly increase the step velocity in the scanned area (in the direction corresponding to dissolution) when the applied contact force is above about 160 nN for the tips employed. The step velocity could be increased at least an order of magnitude by scanning at even higher contact forces (e.g., 270 nN). This enhancement is a function of step orientation relative to the calcite lattice. Indentations near preexisting steps also locally enhance the step velocity. We present evidence that the higher dissolution rates are caused by stress-induced increases in the rate of double-kink nucleation.
The diffusion of oxygen into SiO2 encapsulated polycrystalline CdSe films and the diffusion of indium into polycrystalline CdSe films have been investigated over the temperature range 350 C to 500 C ...using SIMS. The oxygen profiles in the SiO2 indicated that both isotopic oxygen exchange and the diffusion of molecular oxygen along short circuit paths were occurring with activation energies of 1.1 eV and 0.66 eV, respectively. The activation energies determined for the diffusion of the oxygen and indium in the grains (0.39 eV and 0.10 eV, respectively) were smaller than the values determined for the diffusion in the grain boundaries (0.70 eV and 0.78 eV, respectively), and was attributed to impurities and intrinsic defects accumulating at the grain boundaries.
We present a straightforward method for particle identification and background rejection in 3He proportional counters for use in neutron detection. By measuring the risetime and pulse height of the ...preamplifier signals, one may define a region in the risetime versus pulse height space where the events are predominately from neutron interactions. For six proportional counters surveyed in a low-background environment, we demonstrate the ability to reject alpha-particle events with an efficiency of 99%. By applying the same method, we also show an effective rejection of microdischarge noise events that, when passed through a shaping amplifier, are indistinguishable from physical events in the counters. The primary application of this method is in measurements where the signal-to-background for counting neutrons is very low, such as in underground laboratories.
We investigate the effect of low partial pressures of water vapor and bulk temperature on laser-induced positive ion emission from cleaved, single-crystal sodium nitrate and sodium chloride. Both ...materials yield more intense Na
+ emission in the presence of water vapor
(P
H
2
O
∼1×10
−5
Pa)
than samples irradiated under UHV conditions (
P
total<1×10
−7
Pa). Emission intensities increase rapidly with increasing temperature in a fashion consistent with activation energies on the order of 0.07–0.08
eV, both with and without water vapor. We attribute Na
+ emission to a defect-mediated photoelectronic process. Na
+ adsorbed at or near surface anion vacancies (electron traps) is ejected when the underlying or adjacent vacancy is photoionized. Vacancy formation in both materials is expected to have activation energies on the order of 0.08
eV, suggesting that Na
+ emission is rate limited by the production of surface anion vacancies. We attribute the effect of water vapor to defect-mediated sorption that increases the ion emission probability.
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