181 research outputs found
Evaluation of Eu:LiCAF for Neutron Detection Utilizing SiPMs and Portable Electronics
With the increasing cost and decreasing availability of 3He, there have been many efforts to find alternative neutron detection materials. Lithium calcium aluminum fluoride (LiCAF) enriched to 95% 6Li doped with europium was evaluated here as a replacement material for 3He. Wafers 0.5 cm thick, consisting of LiCAF crystals in a rubberized matrix, were embedded with wavelength shifting fibers (WSF) and mated to silicon photo-multipliers (SiPMs) to measure the photon response in a flux of neutrons from a DD neutron generator. Excellent discrimination was realized between neutrons and gammas, and both pulse-height discrimination and pulse-shape analysis were explored. A Figure of Merit (FoM) of 1.03 was achieved. By applying pulse-shape analysis, a simple neutron count output was generated by utilizing a low-pass filter to suppress fast pulses from the SiPM output and subsequently applying a threshold to the remaining signal. Custom electronics were built to bias the SiPMs, then amplify, filter, discriminate, and digitize the LiCAF/WSF scintillation photons, resulting in a digital pulse that can easily be counted with any microcontroller or field programmable gate array. A significant advantage of LiCAF is that it can be fabricated into any shape/size (when embedded in a rubberized matrix), and the light output and transparency is sufficient to allow for thicker scintillators which enable detection of both thermal and epithermal neutrons. This work demonstrated that Eu:LiCAF is capable of discriminating gammas from neutrons and is a potential replacement material for 3He, especially for nuclear security applications and neutron spectroscopy
Neutron Beam Effects on Spin Exchange Polarized He-3
We have observed depolarization effects when high intensity cold neutron
beams are incident on alkali-metal-spin-exchange polarized He-3 cells used as
neutron spin filters. This was first observed as a reduction of the maximum
attainable He-3 polarization and was attributed to a decrease of alkali-metal
polarization, which led us to directly measure alkali-metal polarization and
spin relaxation over a range of neutron fluxes at LANSCE and ILL. The data
reveal a new alkali-metal spin-relaxation mechanism that approximately scales
as the square root of the neutron capture-flux density incident on the cell.
This is consistent with an effect proportional to the recombination-limited ion
concentration, but is much larger than expected from earlier work.Comment: submitted to Physical Review Letter
An accelerator facility for intermediate energy proton irradiation and testing of nuclear materials
The bulk irradiation of materials with 10-30 MeV protons promises to advance
the study of radiation damage for fission and fusion power plants. Intermediate
energy proton beams can now be dedicated to materials irradiation within
university-scale laboratories. This paper describes the first such facility,
with an Ionetix ION-12SC cyclotron producing 12 MeV proton beams. Samples are
mm-scale tensile specimens with thicknesses up to 300 um, mounted to a cooled
beam target with control over temperature. A specialized tensile tester for
radioactive specimens at high temperature (500+ {\deg}C) and/or vacuum
represents the conditions in fission and fusion systems, while a digital image
correlation system remotely measures strain. Overall, the facility provides
university-scale irradiation and testing capability with intermediate energy
protons to complement traditional in-core fission reactor and micro-scale ion
irradiation. This facility demonstrates that bulk proton irradiation is a
scalable and effective approach for nuclear materials research, down-selection,
and qualification.Comment: Submitted to NIM B journa
RACE-IT - Rapid Acute Coronary Syndrome Exclusion using the Beckman Coulter Access high-sensitivity cardiac troponin I: A stepped-wedge cluster randomized trial
Background: Protocols utilizing high-sensitivity cardiac troponin (hs-cTn) assays for the evaluation of suspected acute coronary syndrome (ACS) in the emergency department (ED) have been gaining popularity across the US and the world. These protocols more rapidly rule-out ACS and more accurately identify the presence of acute myocardial injury. At this time, few randomized trials have evaluated the safety and operational impact of these assays, resulting in limited evidence to guide the use and implementation of hs-cTn in the ED.
Objective: The main study objective is to test the effectiveness of a rapid ACS rule-out pathway using hs-cTnI in safely discharging patients from the ED for whom clinical suspicion for ACS exists.
Design: This prospective, implementation trial (n = 11,070) will utilize a stepped wedge cluster randomized trial design. The design will allow for all participating sites to capture benefit from the implementation of the hs-cTnI pathway while providing data evaluating the effectiveness in providing safe and rapid evaluation of patients with clinical suspicion for ACS.
Summary: Demonstrating that clinical pathways using hs-cTnI can be effectively implemented to rapidly rule-out ACS while conserving costly hospital resources has significant implications for the care of patients with possible acute cardiac conditions in EDs across the US.
Clinicaltrialsgov identifier: NCT04488913
Multiple Monoenergetic Gamma Radiography (MMGR) with a compact superconducting cyclotron
Smuggling of special nuclear materials (SNM) and nuclear devices through
borders and ports of entry constitutes a major risk to global security.
Technologies are needed to reliably screen the flow of commerce for the
presence of high- materials such as uranium and plutonium. Here we present
an experimental proof-of-concept of a technique which uses inelastic ()
nuclear reactions to generate monoenergetic photons, which provide means to
measure the areal density and the effective- () of an object
with an accuracy which surpasses that achieved by current methods. We use an
ION-12 superconducting 12~MeV proton cyclotron to produce 4.4,
6.1, 6.9, and 7.1~MeV photons from a variety of nuclear reactions. Using these
photons in a transmission mode we show that we are able to accurately
reconstruct the areal densities and of a test object. This
methodology could enable mobile applications to screen commercial cargoes with
high material specificity, providing a means of distinguishing common cargo
materials from high-Z materials that include uranium and plutonium
A New Measurement of the Radiative Decay Width
High precision measurements of the differential cross sections for
photoproduction at forward angles for two nuclei, C and Pb, have
been performed for incident photon energies of 4.9 - 5.5 GeV to extract the
decay width. The experiment was done at Jefferson
Lab using the Hall B photon tagger and a high-resolution multichannel
calorimeter. The decay width was extracted by
fitting the measured cross sections using recently updated theoretical models
for the process. The resulting value for the decay width is . With the 2.8% total uncertainty, this result is a factor of 2.5 more
precise than the current PDG average of this fundamental quantity and it is
consistent with current theoretical predictions.Comment: 4 pages, 5 figure
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