Publications

Sep, 2026

Conference Paper

From Commissioning to Precision Data-Taking: Resolving Operational Challenges in the Nab Detector Systems

Our understanding of the weak mixing of quarks, described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix, currently presents an anomaly. Thanks to major strides in both theory and experiment, improved precision in determinations of the first row of matrix elements has revealed disagreement with the expectation of unitarity. The Nab experiment at the Spallation Neutron Sourc…

Sep, 2026

Conference Paper

Neutron beta decay measurements with polarized neutrons and the Nab spectrometer

A polarized neutron beam and the Nab spectrometer (pNAB) at the Spallation Neutron Source will enable simultaneous measurements of the beta (A) and neutrino (B) asymmetries in free neutron decay. Combined Nab and pNAB measurements of the correlation parameters a, A, and B will determine the axial-vector to vector coupling ratio in the weak interaction with a precision of a…

Aug, 2026

Journal

Characterization of Low-energy Ionization Signals in Silicon Detectors for the Nab Experiment

The Nab (Neutron a b) experiment is designed to measure the beta-antineutrino angular correlation in free neutron 𝛽 decay with an ultimate precision goal of 0.1%, providing input for tests of Cabibbo-Kobayashi-Maskawa matrix unitarity. This measurement is performed via detection of electrons and protons in delayed coincidence using custom large-area segmented silicon detec…

Mar, 2026

Conference Paper

The Galactic Annihilation Line Explorer (GALE): Balloon-borne Mission to study Galactic 511-keV annihilation emission

The Galactic Annihilation Line Explorer (GALE) mission will address the long-standing question of the sources of Galactic positrons: whether they are produced by unresolved astrophysical sources or created via diffuse processes, possibly due to dark matter decay and/or annihilation. The problem of Galactic positrons that produce 511-keV gamma-ray emission from the Galactic…

Mar, 2026

Conference Paper

Progress Toward Gamma-Ray Imaging for Automated Holdup Measurement in Gloveboxes

Shielded gloveboxes are currently being constructed to facilitate dilution and disposal of many tons of excess plutonium oxide. Measuring holdup in these gloveboxes is expected to be challenging because of the limited available lines of sight through the glovebox shielding. A system of gamma-ray imagers is being developed to provide localization and quantification for hold…

Mar, 2026

Conference Paper

Detailed Characterization of CZT Detector Response for Improved Coded-Aperture Imaging Performance

Gamma-ray imaging is a powerful method for locating and quantifying sources of radiation. The coded-aperture technique demonstrates superior angular resolution in comparison to other methods (e.g., Compton reconstruction). In this method, a mask constructed of highly attenuating material encodes the scene as a shadow pattern on a position-sensitive detector; this pattern c…

Mar, 2026

Conference Paper

Passive Gamma-Ray Imaging as a Verification Tool for Nuclear Weapons Treaties

Mar, 2026

Journal

First full Dalitz plot measurement in neutron 𝛽 decay using the Nab spectrometer and implications for new physics

Precision measurements of observables in neutron 𝛽 decay are used to test the standard model description of the weak interaction and search for evidence of new physics. The Nab experiment at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source was constructed to measure correlations in neutron decay by utilizing an asymmetric spectrometer and novel det…

Dec, 2025

ORNL Report

(U) Air Force Proj Number: 25AD22-2 (Crimson Cloak 2.0) Final Report

Aug, 2025

ORNL Report

Multimodal Data Fusion with 3D Gamma-Ray Imaging for Safeguards 2024 Annual Report

Aug, 2025

Journal

Measurement of the free neutron lifetime in a magneto-gravitational trap with in situ detection

Here we publish three years of data from the UCNτ experiment performed at the Los Alamos Ultracold Neutron Facility at the Los Alamos Neutron Science Center. These data are in addition to our previously published data. Our goals in this paper are to better understand and quantify systematic uncertainties and to improve the lifetime statistical precision. We previously repo…

Jul, 2025

Journal

The pNab experiment and the quest for ever better neutron beam polarization

The Nab and pNAB collaborations are conducting a program of studies of free neutron beta decay, with the primary goal of testing the unitarity of the Cabbibo-Kobayashi-Maskawa matrix that describes quark mixing due to the weak interaction. For this purpose, a large, novel electromagnetic spectrometer, the Nab spectrometer, has been designed, built, and placed in use to det…