47 research outputs found
New Measurements and Quantitative Analysis of Electron Backscattering in the Energy Range of Neutron Beta-Decay
We report on the first detailed measurements of electron backscattering from
plastic scintillator targets, extending our previous work on beryllium and
silicon targets. The scintillator experiment posed several additional
experimental challenges associated with charging of the scintillator target,
and those challenges are addressed in detail. In addition, we quantitatively
compare the energy and angular distributions of this data, and our previous
data, with electron transport simulations based on the Geant4 and Penelope
Monte Carlo simulation codes. The Penelope simulation is found globally to give
a superior description of the data. Such information is crucial for a broad
array of weak-interaction physics experiments, where electron backscattering
can give rise to the dominant detector-related systematic uncertainty.Comment: 7 pages, 3 figure
Emission-aware Energy Storage Scheduling for a Greener Grid
Reducing our reliance on carbon-intensive energy sources is vital for
reducing the carbon footprint of the electric grid. Although the grid is seeing
increasing deployments of clean, renewable sources of energy, a significant
portion of the grid demand is still met using traditional carbon-intensive
energy sources. In this paper, we study the problem of using energy storage
deployed in the grid to reduce the grid's carbon emissions. While energy
storage has previously been used for grid optimizations such as peak shaving
and smoothing intermittent sources, our insight is to use distributed storage
to enable utilities to reduce their reliance on their less efficient and most
carbon-intensive power plants and thereby reduce their overall emission
footprint. We formulate the problem of emission-aware scheduling of distributed
energy storage as an optimization problem, and use a robust optimization
approach that is well-suited for handling the uncertainty in load predictions,
especially in the presence of intermittent renewables such as solar and wind.
We evaluate our approach using a state of the art neural network load
forecasting technique and real load traces from a distribution grid with 1,341
homes. Our results show a reduction of >0.5 million kg in annual carbon
emissions -- equivalent to a drop of 23.3% in our electric grid emissions.Comment: 11 pages, 7 figure, This paper will appear in the Proceedings of the
ACM International Conference on Future Energy Systems (e-Energy 20) June
2020, Australi
A New Solid Deuterium Source of Ultra-Cold Neutrons
In polarized neutron decay, the angular correlation between the neutron spin and the
direction of emission of the electron is characterized by the coefficient A. Measuring
A involves determining the forward-backward asymmetry of the decay beta with
respect to the direction of the neutron polarization. The value of A, when combined
with measurements of the neutron lifetime, determines the values of the vector and
axial vector weak coupling constants, Gv and GA. The value of Gv can also be
determined by measurements of superallowed nuclear beta decay and by requiring
that the Cabibo-Kobayashi-Maskawi (CKM) mixing matrix be unitary along with the
measured value of other elements of the CKM matrix
f(R) actions, cosmic acceleration and local tests of gravity
We study spherically symmetric solutions in f(R) theories and its
compatibility with local tests of gravity. We start by clarifying the range of
validity of the weak field expansion and show that for many models proposed to
address the Dark Energy problem this expansion breaks down in realistic
situations. This invalidates the conclusions of several papers that make
inappropriate use of this expansion. For the stable models that modify gravity
only at small curvatures we find that when the asymptotic background curvature
is large we approximately recover the solutions of Einstein gravity through the
so-called Chameleon mechanism, as a result of the non-linear dynamics of the
extra scalar degree of freedom contained in the metric. In these models one
would observe a transition from Einstein to scalar-tensor gravity as the
Universe expands and the background curvature diminishes. Assuming an adiabatic
evolution we estimate the redshift at which this transition would take place
for a source with given mass and radius. We also show that models of dynamical
Dark Energy claimed to be compatible with tests of gravity because the mass of
the scalar is large in vacuum (e.g. those that also include R^2 corrections in
the action), are not viable.Comment: 26 page
A proposed measurement of the Ă asymmetry in neutron decay with the Los Alamos Ultra-Cold Neutron Source
This article reviews the status of an experiment to study the neutron spin-electron angular correlation with the Los Alamos Ultra-Cold Neutron (UCN) source. The experiment will generate UCNs from a novel solid deuterium, spallation source, and polarize them in a solenoid magnetic field. The experiment spectrometer will consist of a neutron decay region in a solenoid magnetic field combined with several different detector possibilities. An electron beam and a magnetic spectrometer will provide a precise, absolute calibration for these detectors. An A-correlation measurement with a relative precision of 0.2% is expected by the end of 2002
First Measurement of the Neutron -Asymmetry with Ultracold Neutrons
We report the first measurement of angular correlation parameters in neutron
-decay using polarized ultracold neutrons (UCN). We utilize UCN with
energies below about 200 neV, which we guide and store for s in a Cu
decay volume. The potential of a static 7 T field
external to the decay volume provides a 420 neV potential energy barrier to the
spin state parallel to the field, polarizing the UCN before they pass through
an adiabatic fast passage (AFP) spin-flipper and enter a decay volume, situated
within a 1 T, superconducting solenoidal spectrometer. We
determine a value for the -asymmetry parameter , proportional to
the angular correlation between the neutron polarization and the electron
momentum, of .Comment: 4 pages, 2 figures, 1 table, submitted to Phys. Rev. Let
Measurement of Electron Backscattering in the Energy Range of Neutron -Decay
We report on the first detailed measurements of electron backscattering from
low Z targets at energies up to 124 keV. Both energy and angular distributions
of the backscattered electrons are measured and compared with electron
transport simulations based on the Geant4 and Penelope Monte Carlo simulation
codes. Comparisons are also made with previous, less extensive, measurements
and with measurements at lower energies.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
Final results for the neutron ÎČ-asymmetry parameter Aâ from the UCNA experiment
The UCNA experiment was designed to measure the neutron ÎČ-asymmetry parameter A0 using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7âT magnetic field, and then directed to a 1âT solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for A0 was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in 2007, 2008â2009, 2010, and 2011â2013, which ultimately culminated in a 0.67% precision result for Aâ