J. S. Nico

National Institute of Standards and Technology, Maryland, United States

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Publications (93)153.09 Total impact

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    ABSTRACT: The most precise determination of the neutron lifetime using the beam method was completed in 2005 and reported a result of tau_n = (886.3 +/- 1.2 [stat] +/- 3.2 [sys]) s. The dominant uncertainties were attributed to the absolute determination of the fluence of the neutron beam (2.7 s). The fluence was measured with a neutron monitor that counted the neutron-induced charged particles from absorption in a thin, well-characterized 6Li deposit. The detection efficiency of the monitor was calculated from the areal density of the deposit, the detector solid angle, and the ENDF/B-VI 6Li(n,t)4He thermal neutron cross section. In the current work, we have measured the detection efficiency of the same monitor used in the neutron lifetime measurement with a second, totally-absorbing neutron detector. This direct approach does not rely on the 6Li(n,t)4He cross section or any other nuclear data. The detection efficiency is consistent with the value used in 2005 but was measured with a precision of 0.057 %, which represents a five-fold improvement in the uncertainty. We have verified the temporal stability of the neutron monitor through ancillary measurements, allowing us to apply the measured neutron monitor efficiency to the lifetime result from the 2005 experiment. The updated lifetime is tau_n = (887.7 +/- 1.2 [stat] +/- 1.9 [sys]) s.
    Physical Review Letters 11/2013; 111(22):222501. · 7.94 Impact Factor
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    ABSTRACT: Antineutrino detectors operated close to a compact research reactor can provide excellent sensitivity to short-baseline oscillation effects through a precision measurement of the reactor antineutrino spectrum at various distances from the core. We describe a proposed 2-detector experiment with a baseline of 4-20m that will enable a high-precision measurement of the reactor antineutrino spectrum from a highly-enriched uranium core at a US research reactor and provide a definitive search for short-baseline neutrino oscillations. In addition, this experiment will provide important enabling technology for reactor monitoring applications.
    09/2013;
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    ABSTRACT: The characterization of a liquid scintillator incorporating an aqueous solution of enriched lithium chloride to produce a scintillator with 0.40% (6)Li is presented, including the performance of the scintillator in terms of its optical properties and neutron response. The scintillator was incorporated into a fast neutron spectrometer, and the light output spectra from 2.5MeV, 14.1MeV, and (252)Cf neutrons were measured using capture-gated coincidence techniques. The spectrometer was operated without coincidence to perform thermal neutron measurements. Possible improvements in spectrometer performance are discussed.
    Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 03/2013; 77C:130-138. · 1.09 Impact Factor
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    ABSTRACT: We have measured the triple correlation D<ěc J_nrangle/J_n\cdot (ěcβ_e×hat p_ν) with a polarized cold-neutron beam (Mumm et al., Phys Rev Lett 107:102301, 2011; Chupp et al., Phys Rev C 86:035505, 2012). A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation. Final-state effects also contribute to D at the level of 10 - 5 and can be calculated with precision of 1 % or better. The D coefficient is uniquely sensitive to the imaginary part of the ratio of axial-vector and vector beta-decay amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D = [ - 0.94±1.89 (stat)±0.97(sys)]×10 - 4. Assuming only vector and axial vector interactions in beta decay, our result can be interpreted as a measure of the phase of the axial-vector coupling relative to the vector coupling, φ_AV= 180.012^circ ± 0.028^circ. This result also improves constrains on certain non-VA interactions.
    Hyperfine Interactions 03/2013; 214(1-3):97-104. · 0.21 Impact Factor
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    ABSTRACT: This White Paper describes recent progress and future opportunities in the area of fundamental symmetries and neutrinos.
    12/2012;
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    ABSTRACT: We present a straightforward method for particle identification and background rejection in $^3$He 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.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 12/2012; 717. · 1.14 Impact Factor
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    ABSTRACT: As part of an experiment to measure the spectrum of photons emitted in beta-decay of the free neutron, we developed and operated a detector consisting of 12 bismuth germanate (BGO) crystals coupled to avalanche photodiodes (APDs). The detector was operated near liquid nitrogen temperature in the bore of a superconducting magnet and registered photons with energies from 5 keV to 1000 keV. To enlarge the detection range, we also directly detected soft X-rays with energies between 0.2 keV and 20 keV with three large area APDs. The construction and operation of the detector is presented, as well as information on operation of APDs at cryogenic temperatures.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 07/2012; 691. · 1.14 Impact Factor
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    ABSTRACT: Background: Time-reversal-invariance violation, or equivalently CP violation, may explain the observed cosmological baryon asymmetry as well as signal physics beyond the Standard Model. In the decay of polarized neutrons, the triple correlation D<J_{n}>\cdot(p_{e}\timesp_{\nu}) is a parity-even, time-reversal- odd observable that is uniquely sensitive to the relative phase of the axial-vector amplitude with respect to the vector amplitude. The triple correlation is also sensitive to possible contributions from scalar and tensor amplitudes. Final-state effects also contribute to D at the level of 1e-5 and can be calculated with a precision of 1% or better. Purpose: We have improved the sensitivity to T-odd, P-even interactions in nuclear beta decay. Methods: We measured proton-electron coincidences from decays of longitudinally polarized neutrons with a highly symmetric detector array designed to cancel the time-reversal-even, parity-odd Standard-Model contributions to polarized neutron decay. Over 300 million proton-electron coincidence events were used to extract D and study systematic effects in a blind analysis. Results: We find D = [-0.94\pm1.89(stat)\pm0.97(sys)]e-4. Conclusions: This is the most sensitive measurement of D in nuclear beta decay. Our result can be interpreted as a measurement of the phase of the ratio of the axial-vector and vector coupling constants (CA/CV= |{\lambda}|exp(i{\phi}_AV)) with {\phi}_AV = 180.012{\deg} \pm0.028{\deg} (68% confidence level) or to constrain time-reversal violating scalar and tensor interactions that arise in certain extensions to the Standard Model such as leptoquarks. This paper presents details of the experiment, analysis, and systematic- error corrections.
    Physical Review C 05/2012; 86(3). · 3.72 Impact Factor
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    ABSTRACT: The Proceedings of the 2011 workshop on Fundamental Physics at the Intensity Frontier. Science opportunities at the intensity frontier are identified and described in the areas of heavy quarks, charged leptons, neutrinos, proton decay, new light weakly-coupled particles, and nucleons, nuclei, and atoms.
    05/2012;
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    ABSTRACT: This white paper addresses the hypothesis of light sterile neutrinos based on recent anomalies observed in neutrino experiments and the latest astrophysical data.
    04/2012;
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    ABSTRACT: We have measured the triple correlation D . (pe × pv) with a polarized cold-neutron beam at the NIST Center for Neutron Research by observing proton-electron coincidences in the decay of polarized neutrons. A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation due to the CPT theorem. Final-state effects also contribute to D at the level of 10-5 and can be calculated with precision of 1% or better. The D coefficient is sensitive to the phase, of λ the ratio of axial-vector and vector amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics such as leptoquarks. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D = [-0.96+/-1.89(stat)+/-1.01(sys)]×10-4.
    04/2012;
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    ABSTRACT: An alpha-gamma counter was used to measure the absolute neutron flux of a monochromatic cold neutron beam to sub-0.1,% precision. Simultaneously, the counter was used to calibrate a thin neutron flux monitor based on neutron absorption on ^6Li to the same precision. This monitor was used in the most precise beam-based measurement of the neutron lifetime, where the limiting systematic effect was the uncertainty in the neutron counting efficiency (0.3,%). The counter uses a thick target of ^10B-enriched boron carbide to completely absorb the beam. The rate of absorbed neutrons is determined by counting 478 keV gamma rays from neutron capture on ^10B with calibrated high-purity germanium detectors. The calibration results and the implications for the neutron lifetime will be discussed.
    Bulletin of the Amer. Phys. Soc. 03/2012; 57(3).
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    ABSTRACT: The status of the feasibility studies for a proposed Ga source experiment to search for possible electron neutrino transitions into sterile states is presented. The advantages of the proposed technique are considered. The experiment has the potential to detect neutrino oscillation transitions with mass-squared difference Δm2 > 0.5 eV2 with a sensitivity to disappearance of electron neutrinos of a few percent
    Journal of Physics Conference Series 01/2012; 375(4).
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    ABSTRACT: We report the results of an improved determination of the triple correlation DP·(p(e)×p(v)) that can be used to limit possible time-reversal invariance in the beta decay of polarized neutrons and constrain extensions to the standard model. Our result is D=[-0.96±1.89(stat)±1.01(sys)]×10(-4). The corresponding phase between gA and gV is ϕAV=180.013°±0.028° (68% confidence level). This result represents the most sensitive measurement of D in nuclear β decay.
    Physical Review Letters 09/2011; 107(10):102301. · 7.94 Impact Factor
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    ABSTRACT: We report on the development of a fast neutron detector using a liquid scintillator doped with enriched Li-6. The lithium was introduced in the form of an aqueous LiCl micro-emulsion with a di-isopropylnaphthalene-based liquid scintillator. A Li-6 concentration of 0.15 % by weight was obtained. A 125 mL glass cell was filled with the scintillator and irradiated with fission-source neutrons. Fast neutrons may produce recoil protons in the scintillator, and those neutrons that thermalize within the detector volume can be captured on the Li-6. The energy of the neutron may be determined by the light output from recoiling protons, and the capture of the delayed thermal neutron reduces background events. In this paper, we discuss the development of this 6Li-loaded liquid scintillator, demonstrate the operation of it in a detector, and compare its efficiency and capture lifetime with Monte Carlo simulations. Data from a boron-loaded plastic scintillator were acquired for comparison. We also present a pulse-shape discrimination method for differentiating between electronic and nuclear recoil events based on the Matusita distance between a normalized observed waveform and nuclear and electronic recoil template waveforms. The details of the measurements are discussed along with specifics of the data analysis and its comparison with the Monte Carlo simulation.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2011; 646. · 1.14 Impact Factor
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    ABSTRACT: We report an upper bound on parity-violating neutron spin rotation in 4He. This experiment is the most sensitive search for neutron-weak optical activity yet performed and represents a significant advance in precision in comparison to past measurements in heavy nuclei. The experiment was performed at the NG-6 slow-neutron beamline at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Our result for the neutron spin rotation angle per unit length in 4He is dϕ/dz=[+1.7±9.1(stat.)±1.4(sys.)]×10-7 rad/m. The statistical uncertainty is smaller than current estimates of the range of possible values of dϕ/dz in n+4He.
    Physical Review C 01/2011; 83(2):022501(R). · 3.72 Impact Factor
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    ABSTRACT: Measurements of parity-violating neutron spin rotation can provide insight into the poorly understood nucleon–nucleon weak interaction. Because the expected rotation angle per unit length is small (10−7 rad/m), several properties of the polarized cold neutron beam phase space and the neutron optical elements of the polarimeter must be measured to quantify possible systematic effects. This paper presents (1) an analysis of a class of possible systematic uncertainties in neutron spin rotation measurements associated with the neutron polarimetry, and (2) measurements of the relevant neutron beam properties (intensity distribution, energy spectrum, and the product of the neutron beam polarization and the analyzing power as a function of the beam phase space properties) on the NG-6 cold neutron beam-line at the National Institute of Standards and Technology Center for Neutron Research. We conclude that the phase space nonuniformities of the polarimeter in this beam are small enough that a parity-violating neutron spin rotation measurement in n-4He with systematic uncertainties at the 10−7 rad/m level is possible.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; · 1.14 Impact Factor
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    ABSTRACT: We present results for detection of X-rays by large area avalanche photodiodes (APDs) in strong magnetic fields and at cryogenic temperatures. Whereas at room temperature we observe essentially no effects on the response, at cryogenic temperature we observe significant distortion when the magnetic field is in the plane of the APD surface (and thus perpendicular to the electric field in the APD). At all temperatures, effects are minor when the magnetic field is normal to the APD surface (and thus parallel to the electric field in the APD). We performed measurements of the response of an APD to illumination by X-rays in fields between 0 and 4.6 T, for temperatures between 77 and 250 K. Measurements were performed using 241Am and 55Fe sources, and 1.5 keV X-rays produced by aluminum fluorescence. The data indicate that the effects are associated with those X-rays that are absorbed in the drift region of the APD.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; 652:520-523. · 1.14 Impact Factor
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    ABSTRACT: The measurements of the neutron lifetime using "bottled" ultra-cold neutrons that claim the smallest experimental uncertainties are seriously discrepant with respect to each other. Given that the statistical contribution to their uncertainty is much smaller than the discrepancy, it is likely that one or more of these measurements suffers from a systematic effect yet to be definitively identified. In the most precise cold neutron beam measurement of the lifetime which gives taun= (886.3 ±3.4) s, the largest uncertainty was attributed to the absolute determination of the capture flux of the neutron beam. A new direct measurement of the neutron lifetime flux monitor efficiency using an absolute "black" neutron detector could reduce this contribution to the uncertainty. The Alpha-Gamma device is a "black" neutron detector based on the counting of 478 keV gamma rays from a totally absorbing 10B foil. Neutron flux is measured to a statistical precision of 0.1% in several days of running. The Alpha-Gamma device has been used to calibrate the neutron lifetime flux monitor on a monochromatic beamline at the NIST Center for Neutron Research. The measurement technique and status of this calibration will be presented.
    Bulletin of the Amer. Phys. Soc. 11/2010; 55(14):30.
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    ABSTRACT: Fast neutrons induced by natural radioactivity and cosmic rays are important sources of background for low-background searches of dark matter, neutrinoless double beta decay, and solar neutrinos. One method for performing fast neutron spectroscopy involves a capture-gated coincidence between a fast neutron that thermalizes through elastic scattering within an organic scintillator and its subsequent capture on a nuclide having a high thermal neutron capture cross section. Thermalization within an organic scintillator occurs within a few ns, but the neutron capture time is typically of order 10s to 100s of mus. A capture signal preceded by a thermalization signal within a characteristic time can be used to select those fast neutrons that have deposited all of their kinetic energy into the scintillator, and the thermalization signal can provide spectroscopic information. We report on a number of measurements performed to characterize the properties of an organic liquid scintillator based on di-isopropyl naphthalene and loaded with ^6Li. This work has been carried out within a joint UMd and NIST project to develop a fast neutron spectrometer suitable for use in a deep underground, low-background laboratory. In particular, we report on measurements of optical properties, light yield, and fast neutron response.
    11/2010;

Publication Stats

226 Citations
328 Downloads
153.09 Total Impact Points

Institutions

  • 1995–2013
    • National Institute of Standards and Technology
      Maryland, United States
    • Louisiana State University
      Baton Rouge, Louisiana, United States
  • 2009
    • Tulane University
      New Orleans, Louisiana, United States
  • 1992–2006
    • Los Alamos National Laboratory
      Los Alamos, California, United States
  • 1994
    • Princeton University
      Princeton, New Jersey, United States