Session K12: Instrumentation

Noise Studies of Polarimetry Systems for Polarized $^{3}$He Targets

The NMR technique of adiabatic fast passage (AFP) often plays an important role in monitoring the polarization of $^{3}$He targets polarized using spin-exchange optical pumping. The absolute calibration of such AFP-based polarimetry systems can be accomplished by comparing, either directly or indirectly, with the AFP signals of thermally polarized water. At the low magnetic fields at which spin-exchange polarized $^{3}$He targets are run, however, identifying water signals amidst noise caused by external electromagnetic interferences and microphonics can be challenging. In this talk we will present results obtained from thermally polarized water samples at a field of 36 gauss with a signal-to-noise ratio greater than 10 in a single measurement. The measurements were obtained by using a specially designed NMR apparatus which includes a suspension system to suppress mechanical vibrations and shielding to reduce electromagnetic interference. Our system is part of an effort to improve polarimetry of polarized $^{3}$He targets, and also provides insight into systematic effects related to the use of thermally polarized water for the calibration of low-field AFP-based NMR systems.   

An efficient and cost-effective microchannel plate detector for slow neutron radiography

A novel approach for efficiently imaging objects with slow neutrons in two dimensions is described. Neutron sensitivity is achieved by use of a boron doped microchannel plate (MCP). The resulting electron avalanche is further amplified with a Z-stack MCP before being sensed by two orthogonally oriented wire planes. Coupling of the wire planes to delay lines efficiently encodes the position information as a time difference. To determine the position resolution, slow neutrons were used to illuminate a Cd-mask placed directly in front of the detector. Peaks in the resulting spectrum exhibited an average peak width of 329 $\mu$m FWHM, corresponding to an average intrinsic resolution of 216 $\mu$m. The center region of the detector exhibits a significantly better spatial resolution with an intrinsic resolution of $<$ 100 $\mu$m observed.   

Construction of an Electromagnetic Calorimeter with Thermal Annealing of Lead Glass in Situ

The construction of a new Electromagnetic Calorimeter is underway for the Super BigBite Spectrometer at Jefferson Lab for the purpose of significantly improving the experimental measurement of the proton electric form factor (GEp-E12-07-109) from the reaction p($\vec$e, e$^{\prime}$ $\vec$p). The well-known problem of radiation damage of lead glass calorimeters from high luminosity experiments such as GEp is being addressed in this design. A novel approach is taken to design a system for continuous thermal annealing in situ to experimental operation. Also, the careful selection of lead glass and light guide materials is found to be very important toward achieving higher signal efficiency and stronger structural strength for the core detector elements. A description of the design and construction of the calorimeter will be presented along with preliminary results from bench tests on some of the subassemblies of the instrument.   

Development of the 30 keV Proton Source and Detector Systems at the University of Manitoba for the Nab Experiment

The ``Nab'' collaboration will perform a precise measurement of the neutron beta decay parameters ``a'' and ``b'', which constitutes a test for physics beyond the standard model.~ The experiment makes use of the fundamental physics cold neutron beamline at the Spallation Neutron Source at the Fundamental Neutron Physics Beam Line.~ This experiment requires very efficient and precise detection of low energy (30 keV) protons with large area Si detectors.~ To this end, a 30 keV proton source has been built at the University of Manitoba (UofM) to characterize the Si detector with respect to a custom large area (150mm x 150mm) microchannel plate detector, with known detection efficiency. During development of the MCP detector, a large area (200 mm diameter) phosphor screen has been employed to characterize the steering mechanism of the proton beam. This talk will introduce the 30 keV proton source at UofM and present the steering mechanism results as measured by the phosphor screen and microchannel plate detector.   

Construction of a Thick-Crystal Neutron Interferometer Using New Fabrication Techniques

The construction of a monolithic, thick crystal, ``perfect" silicon neutron interferometer using a ultra-high precision grinding technique and a combination of annealing and chemical etching that differs from the construction of prior neutron interferometers is described. Under these fabrication conditions, the interferometer exhibits an excellent interference fringe visibility of 80\%. The interferometer was tested throughout the post fabrication process, and perturbations to the expected interference signal are found to correspond to subsurface damage that is alleviated through a combination of annealing and chemical etching. These fabrication techniques can be extended to other neutron interferometers or experiments using Bragg-diffracting crystals, where the crystal shape and the integrity of the Bragg planes at the crystal surface are important.   

Abstract Withdrawn

The temperature dependence of electrical conductivity of high purity germanium (HPGe) crystal samples has been investigated in the temperature range from 7 to 100 K. The conductivity versus inverse of temperature curves for all the samples are divided into three distinct temperature ranges: (a) the high temperature range, where the conductivity increases to a maximum with decreasing temperature, (b) medium temperature range, where the conductivity decreases proportionally with decreasing temperature, and (c) low temperature range where the conductivity continues decreasing slowly with decreasing temperature. Furthermore, the net carrier concentrations of all samples have been calculated based on measured conductivity in the whole measurement temperature range. The calculated results show that the net carrier concentration increases with increasing temperature due to thermal excitation, but it reaches saturation around 40K. Also, the calculated results at 77K match the experimental results by van der Paul Hall measurement very well for all investigated samples. We acknowledge financial support from DOE DE-FG02-10ER46709, NSF OISE-1743790, NSF OIA-1738632 and the state of South Dakota   

Verification Datasets from Project 8 Development

The Project 8 neutrino experiment seeks to determine the absolute neutrino mass scale by measuring the energy of electrons from beta decays, using a novel technique. The technique, called Cyclotron Radiation Emission Spectroscopy (CRES), has been demonstrated at the single-electron scale. In addition to the standard checks for known decay peaks in the energy spectrum, the CRES data can be validated by injecting tones of known frequency, or by observing the CRES emitted by a free electron that is driven by an injected RF wave. The status of these cross-checks will be discussed within the context of planning future development of Project~8.