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J. S. Nico

Publications and source records attributed to J. S. Nico.

At least 19 recordsLinked to original sources
arXiv2026

Precision measurement of radiative neutron \b{eta}-decay: methodology and systematic effects

In the Standard Model the free neutron decays to a proton, an electron, and an antineutrino along with a continuous spectrum of photons. In 2016 the RDK II collaboration reported on a measurement of the photon energy spectrum and branching ratio over the range of 0.4 keV to the 782 keV endpoint using two different detector arrays. In the experiment, the radiative decay photons were observed in coincidence with the decay electrons and protons. In this paper, we present details of the analysis, including the determination of the systematic corrections and uncertainties and comparison of measured particle and photon energy spectra to Monte Carlo simulations. We conclude with approaches to improving the precision of these measurements.

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arXiv2025

Detection of molecular hydrogen in a neutron beam lifetime experiment

One method of determining the free neutron lifetime involves the absolute counting of neutrons and trapped decay protons. In such experiments, a cold neutron beam traverses a segmented proton trap inside a superconducting solenoid while the neutron flux is continuously monitored. Protons that are born within the fiducial volume of the trap are confined radially by the magnetic field and axially by the electrostatic potential supplied by trap electrodes. They are periodically released and counted, and the ratio of the absolute number of neutrons to protons is proportional to the neutron lifetime. Systematic error can be introduced if protons in the trap are lost, gained, or misidentified. The influence of molecular hydrogen interactions is of particular interest because of its ubiquitous presence in ultrahigh vacuum systems. To understand how it could affect the neutron lifetime, measurements were performed on the production and detection of molecular hydrogen in an apparatus used to measure the neutron lifetime. We demonstrate that charge exchange with molecular hydrogen can occur with trapped protons, and we determine the efficiency with which the molecular hydrogen ions in the trap are detected. Finally, we comment on the potential impact on a neutron lifetime experiment using this beam technique. We find that the result of the beam neutron lifetime performed at NIST is unlikely to have been significantly affected by charge exchange with molecular hydrogen.

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arXiv2024

Recoil-Order and Radiative Corrections to the aCORN Experiment

The aCORN experiment measures the electron-antineutrino $a$-coefficient in free neutron decay. We update the previous aCORN results to include radiative and recoil corrections to first order, and discuss a key issue in the comparison of results from different $a$-coefficient experimental methods when these effects are considered. The corrected combined result is $\overline{a} = -0.10779 \pm 0.00125\, ({\rm stat}) \pm 0.00133\, ({\rm sys})$, averaged over the full Fermi neutron beta spectrum. The corresponding corrected result for the ratio of weak coupling constants $λ= G_A/G_V$ is $λ= -1.2712 \pm 0.0061$. This improves agreement with previous $a$-coefficient experiments, in particular the 2020 aSPECT result

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arXiv2022

Comments on Systematic Effects in the NIST Beam Neutron Lifetime Experiment

We discuss issues raised by Serebrov, et al. in a recent paper regarding systematic effects in the beam neutron lifetime experiment performed at NIST. We show that these effects were considered in the original analyses and that our corrections and systematic uncertainties were appropriate. We point out some misconceptions and erroneous assumptions in the analysis of Serebrov, et al. None of the issues raised in Serebrov, et al lead us to alter the value of the neutron lifetime reported previously.

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arXiv2022

A Search for Electron Neutrino Transitions to Sterile States in the BEST Experiment

The Baksan Experiment on Sterile Transitions (BEST) probes the gallium anomaly and its possible connections to oscillations between active and sterile neutrinos. Based on the Gallium-Germanium Neutrino Telescope (GGNT) technology of the SAGE experiment, BEST employs two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Oscillations on this short scale could produce deficits in the $^{71}$Ge production rates within the two zones, as well as a possible rate difference between the zones. From July 5th to October 13th 2019, the two-zone target was exposed to a primarily monoenergetic, 3.4-MCi $^{51}$Cr neutrino source 10 times for a total of 20 independent $^{71}$Ge extractions from the two Ga targets. The $^{71}$Ge production rates from the neutrino source were measured from July 2019 to March 2020. At the end of these measurements, the counters were filled with $^{71}$Ge doped gas and calibrated during November 2020. In this paper, results from the BEST sterile neutrino oscillation experiment are presented in details. The ratio of the measured $^{71}$Ge production rates to the predicted rates for the inner and the outer target volumes are calculated from the known neutrino capture cross section. Comparable deficits in the measured ratios relative to predicted values are found for both zones, with the $4 σ$ deviations from unity consistent with the previously reported gallium anomaly. If interpreted in the context of neutrino oscillations, the deficits give best fit oscillation parameters of $Δm^2=3.3^{+\infty}_{-2.3}$ eV$^2$ and sin$^2 2θ=0.42^{+0.15}_{-0.17}$, consistent with $ν_e \rightarrow ν_s$ oscillations governed by a surprisingly large mixing angle.

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arXiv2022

Results from the Baksan Experiment on Sterile Transitions (BEST)

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos, $ν_{e}$, observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the \textit{gallium anomaly}, which could be interpreted as evidence for oscillations between $ν_e$ and sterile neutrino ($ν_s$) states. A 3.414-MCi \nuc{51}{Cr} $ν_e$ source was placed at the center of two nested Ga volumes and measurements were made of the production of \nuc{71}{Ge} through the charged current reaction, \nuc{71}{Ga}($ν_e$,e$^-$)\nuc{71}{Ge}, at two average distances. The measured production rates for the inner and the outer targets respectively are ($54.9^{+2.5}_{-2.4}(\mbox{stat})\pm1.4 (\mbox{syst})$) and ($55.6^{+2.7}_{-2.6}(\mbox{stat})\pm1.4 (\mbox{syst})$) atoms of \nuc{71}{Ge}/d. The ratio ($R$) of the measured rate of \nuc{71}{Ge} production at each distance to the expected rate from the known cross section and experimental efficiencies are $R_{in}=0.79\pm0.05$ and $R_{out}= 0.77\pm0.05$. The ratio of the outer to the inner result is 0.97$\pm$0.07, which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20-24\% lower than expected, thus reaffirming the anomaly. These results are consistent with $ν_e \rightarrow ν_s$ oscillations with a relatively large $Δm^2$ ($>$0.5 eV$^2$) and mixing sin$^2 2θ$ ($\approx$0.4).

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arXiv2020

Measurement of the neutron decay electron-antineutrino angular correlation by the aCORN experiment

The aCORN experiment measures the neutron decay electron-antineutrino correlation ($a$-coefficient) using a novel method based on an asymmetry in proton time-of-flight for events where the beta electron and recoil proton are detected in delayed coincidence. We report the data analysis and result from the second run at the NIST Center for Neutron Research, using the high-flux cold neutron beam on the new NG-C neutron guide end position: $a = -0.10758 \pm 0.00136 (\mbox{stat}) \pm 0.00148 (\mbox{sys})$. This is consistent within uncertainties with the result from the first aCORN run on the NG-6 cold neutron beam. Combining the two aCORN runs we obtain $a = -0.10782 \pm 0.00124 (\mbox{stat}) \pm 0.00133 (\mbox{sys})$, which has an overall relative standard uncertainty of 1.7 \%. The corresponding result for the ratio of weak coupling constants $λ= G_A/G_V$ is $λ= -1.2796\pm 0.0062$.

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arXiv2019

Experimental Upper Bound and Theoretical Expectations for Parity-Violating Neutron Spin Rotation in 4He

Neutron spin rotation is expected from quark-quark weak interactions in the Standard Model, which induce weak interactions among nucleons that violate parity. We present the results from an experiment searching for the effect of parity violation via the spin rotation of polarized neutrons in a liquid $^{4}$He medium. The value for the neutron spin rotation angle per unit length in $^{4}$He, $dϕ/dz =(+2.1 \pm 8.3 (stat.) \pm 2.9 (sys.))\times10^{-7}$ rad/m, is consistent with zero. The result agrees with the best current theoretical estimates of the size of nucleon-nucleon weak amplitudes from other experiments and with the expectations from recent theoretical approaches to weak nucleon-nucleon interactions. In this paper we review the theoretical status of parity violation in the $\vec{n}+^{4}$He system and discuss details of the data analysis leading to the quoted result. Analysis tools are presented that quantify systematic uncertainties in this measurement and that are expected to be essential for future measurements.

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arXiv2018

Measurement of the electron-antineutrino correlation in neutron beta decay: aCORN experiment

The aCORN experiment uses a novel asymmetry method to measure the electron-antineutrino correlation (a-coefficient) in free neutron decay that does not require precision proton spectroscopy. aCORN completed two physics runs at the NIST Center for Neutron Research. The first run on the NG-6 beam line in 2013--2014 obtained the result a = 0.1090 +/- 0.0030 (stat) +/- 0.0028 (sys), a total uncertainty of 3.8%. The second run on the new NG-C high flux beam line promises an improvement in precision to <2%.

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arXiv2018

Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using a method of an alpha-gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024 %. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058 %. We discuss the principle of the alpha-gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.

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arXiv2017

aCORN: an experiment to measure the electron-antineutrino correlation coefficient in free neutron decay

We describe an apparatus used to measure the electron-antineutrino angular correlation coefficient in free neutron decay. The apparatus employs a novel measurement technique in which the angular correlation is converted into a proton time-of-flight asymmetry that is counted directly, avoiding the need for proton spectroscopy. Details of the method, apparatus, detectors, data acquisition, and data reduction scheme are presented, along with a discussion of the important systematic effects.

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arXiv2017

The aCORN Backscatter-Suppressed Beta Spectrometer

Backscatter of electrons from a beta spectrometer, with incomplete energy deposition, can lead to undesirable effects in many types of experiments. We present and discuss the design and operation of a backscatter-suppressed beta spectrometer that was developed as part of a program to measure the electron-antineutrino correlation coefficient in neutron beta decay (aCORN). An array of backscatter veto detectors surrounds a plastic scintillator beta energy detector. The spectrometer contains an axial magnetic field gradient, so electrons are efficiently admitted but have a low probability for escaping back through the entrance after backscattering. The design, construction, calibration, and performance of the spectrometer are discussed.

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arXiv2016

Precision Measurement of the Radiative $\Beta$ Decay of the Free Neutron

The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the $β$ decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782~keV. The spectral shape was consistent with theory, and we determined a branching ratio of 0.00335 $\pm$ 0.00005 [stat] $\pm$ 0.00015 [syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14~keV. For this array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582 $\pm$ 0.00023 [stat] $\pm$ 0.00062 [syst]. We report the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies.

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arXiv2015

Development and Characterization of a High Sensitivity Segmented Fast Neutron Spectrometer (FaNS-2)

We present the development of a segmented fast neutron spectrometer (FaNS-2) based upon plastic scintillator and $^3$He proportional counters. It was designed to measure both the flux and spectrum of fast neutrons in the energy range of few MeV to 1 GeV. FaNS-2 utilizes capture-gated spectroscopy to identify neutron events and reject backgrounds. Neutrons deposit energy in the plastic scintillator before capturing on a $^3$He nucleus in the proportional counters. Segmentation improves neutron energy reconstruction while the large volume of scintillator increases sensitivity to low neutron fluxes. A main goal of its design is to study comparatively low neutron fluxes, such as cosmogenic neutrons at the Earth's surface, in an underground environment, or from low-activity neutron sources. In this paper, we present details of its design and construction as well as its characterization with a calibrated $^{252}$Cf source and monoenergetic neutron fields of 2.5 MeV and 14 MeV. Detected monoenergetic neutron spectra are unfolded using a Singular Value Decomposition method, demonstrating a 5% energy resolution at 14 MeV. Finally, we discuss plans for measuring the surface and underground cosmogenic neutron spectra with FaNS-2.

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arXiv2015

Nonproportionality in the scintillation light yield of bismuth germanate

We present measurements of nonproportionality in the scintillation light yield of bismuth germanate (BGO) for gamma-rays with energies between 6 keV and 662 keV. The scintillation light was read out by avalanche photodiodes (APDs) with both the BGO crystals and APDs operated at a temperature of approximately 90 K. Data were obtained using radioisotope sources to illuminate both a single BGO crystal in a small test cryostat and a 12-element detector in a neutron radiative beta-decay experiment. In addition one datum was obtained in a 4.6 T magnetic field based on the bismuth K x-ray escape peak produced by a continuum of background gamma rays in this apparatus. These measurements and comparison to prior results were motivated by an experiment to study the radiative decay mode of the free neutron. The combination of data taken under different conditions yields a reasonably consistent picture for BGO nonproportionality that should be useful for researchers employing BGO detectors at low gamma ray energies.

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arXiv2015

PROSPECT - A Precision Reactor Oscillation and Spectrum Experiment at Short Baselines

Current models of antineutrino production in nuclear reactors predict detection rates and spectra at odds with the existing body of direct reactor antineutrino measurements. High-resolution antineutrino detectors operated close to compact research reactor cores can produce new precision measurements useful in testing explanations for these observed discrepancies involving underlying nuclear or new physics. Absolute measurement of the 235U-produced antineutrino spectrum can provide additional constraints for evaluating the accuracy of current and future reactor models, while relative measurements of spectral distortion between differing baselines can be used to search for oscillations arising from the existence of eV-scale sterile neutrinos. Such a measurement can be performed in the United States at several highly-enriched uranium fueled research reactors using near-surface segmented liquid scintillator detectors. We describe here the conceptual design and physics potential of the PROSPECT experiment, a U.S.-based, multi-phase experiment with reactor-detector baselines of 7-20 meters capable of addressing these and other physics and detector development goals. Current R&D status and future plans for PROSPECT detector deployment and data-taking at the High Flux Isotope Reactor at Oak Ridge National Laboratory will be discussed.

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arXiv2014

Fast Neutron Detection with a Segmented Spectrometer

A fast neutron spectrometer consisting of segmented plastic scintillator and He-3 proportional counters was constructed for the measurement of neutrons in the energy range 1 MeV to 200 MeV. We discuss its design, principles of operation, and the method of analysis. The detector is capable of observing very low neutron fluxes in the presence of ambient gamma background and does not require scintillator pulseshape discrimination. The spectrometer was characterized for its energy response in fast neutron fields of 2.5 MeV and 14 MeV, and the results are compared with Monte Carlo simulations. Measurements of the fast neutron flux and energy response at 120 m above sea-level (39.130 deg. N, 77.218 deg. W) and at a depth of 560 m in a limestone mine are presented. Finally, the design of a spectrometer with improved sensitivity and energy resolution is discussed.

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