An electron transparent proton detector for neutron decay studies

9 páginas, 12 figuras, 4 tablas.We have developed an ultrathin (<100 nm), very strong polyimide foil which can span more than 6×6 cm2 and is ideal for the fabrication of low energy proton detectors. We have produced a proton detector geometry in which protons incident on the foil with kinetic energies greater than about 25 keV produce, on average, more than ten secondary electrons in a conversion crystal evaporated on the back face of the foil. These secondary electrons can be "postaccelerated" and counted in a variety of detectors. The polyimide foils are much more durable than carbon foils previously used in similar detection geometries. LiF was chosen as the conversion crystal, which is relatively insensitive to exposure to air, improving their secondary electron yield under typical operating conditions. In addition, we describe the operation of a very simple, small scale proton accelerator and detector testing chamber capable of providing up to 10 kHz of beam with energies between 10 and 50 keV onto a biased target with a maximum ion contamination of 0.5%.This research was funded through DOE Grant Nos. DEFG02- 97ER41033, DE-FG02-03ER41231, DE-FG02- 97ER41042 and NSF Grant Nos. 0100689 and 9807133. Thanks also to Bicron Inc. for the CSI crystal.Peer reviewe

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

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

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

Electron-capture branch of 100Tc and tests of nuclear wave functions for double-beta decays

We present a measurement of the electron-capture branch of $^{100}$Tc. Our value, $B(\text{EC}) = (2.6 \pm 0.4) \times 10^{-5}$, implies that the $^{100}$Mo neutrino absorption cross section to the ground state of $^{100}$Tc is roughly one third larger than previously thought. Compared to previous measurements, our value of $B(\text{EC})$ prevents a smaller disagreement with QRPA calculations relevant to double-$\beta$ decay matrix elements

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 ß 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 β\beta-Asymmetry with Ultracold Neutrons

We report the first measurement of angular correlation parameters in neutron $\beta$-decay using polarized ultracold neutrons (UCN). We utilize UCN with energies below about 200 neV, which we guide and store for $\sim 30$ s in a Cu decay volume. The $\vec{\mu}_n \cdot \vec{B}$ 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, $2 \times 2\pi$ superconducting solenoidal spectrometer. We determine a value for the $\beta$-asymmetry parameter $A_0$, proportional to the angular correlation between the neutron polarization and the electron momentum, of $A_0 = -0.1138 \pm 0.0051$.Comment: 4 pages, 2 figures, 1 table, submitted to Phys. Rev. Let