Brent A. VanDevender

Single-electron detection and spectroscopy via relativistic cyclotron radiation

It has been understood since 1897 that accelerating charges must emit electromagnetic radiation. Although first derived in 1904, cyclotron radiation from a single electron orbiting in a magnetic field has never been observed directly. We demonstrate single-electron detection in a novel radio-frequency spectrometer. The relativistic shift in the cyclotron frequency permits a precise electron energy measurement. Precise beta electron spectroscopy from gaseous radiation sources is a key technique in modern efforts to measure the neutrino mass via the tritium decay end point, and this work demonstrates a fundamentally new approach to precision beta spectroscopy for future neutrino mass experiments.

The C-4 dark matter experiment

We describe the experimental design of C-4, an expansion of the CoGeNT dark matter search to four identical detectors each approximately three times the mass of the p-type point contact germanium diode presently taking data at the Soudan Underground Laboratory. Expected reductions of radioactive backgrounds and energy threshold are discussed, including an estimate of the additional sensitivity to low- mass dark matter candidates to be obtained with this search.

High-Purity Germanium Spectroscopy at Rates in Excess of

In gamma spectroscopy, a compromise must be made between energy resolution and event-rate capability. Some foreseen nuclear material safeguards applications require a spectrometer with energy resolution typical of high purity germanium (HPGe) detectors, operated at event rates up to and exceeding 106 per second. We report the performance of an HPGe spectrometer system adapted to run under such conditions. Our system consists of a commercial semi-coaxial HPGe detector, a modified high-voltage-rail, resistive-feedback, charge-sensitive preamplifier and a continuous waveform digitizer. Digitized waveforms are analyzed offline with a novel time-variant trapezoidal filter algorithm. Several time-invariant trapezoidal filters are run in parallel and the slowest one not rejected by instantaneous pileup conditions is used to measure each pulse height. We have attained full-width-at-half-maximum energy resolution approximately 8 keV measured at 662 keV with 1.03 ×106 per second incoming event rate and 39% throughput. An additional constraint on the width of the fast trigger filter removes a significant amount of rising edge pileup that passes the first pileup cut, reducing throughput to 25%. While better resolution has been reported by other authors, our throughput is an order of magnitude higher than any other reported HPGe system operated at such an event rate.

10^{6}

Semiconductor detectors in general have a dead layer at their surfaces that is either a result of natural or induced passivation, or is formed during the process of making a contact. Charged particles passing through this region produce ionization that is incompletely collected and recorded, which leads to departures from the ideal in both energy deposition and resolution. The silicon p–i–n diode used in the KATRIN neutrino-mass experiment has such a dead layer. We have constructed a detailed Monte Carlo model for the passage of electrons from vacuum into a silicon detector, and compared the measured energy spectra to the predicted ones for a range of energies from 12 to 20 keV. The comparison provides experimental evidence that a substantial fraction of the ionization produced in the “dead” layer evidently escapes by diffusion, with 46% being collected in the depletion zone and the balance being neutralized at the contact or by bulk recombination. The most elementary model of a thinner dead layer from which no charge is collected is strongly disfavored.

Events/s

This paper presents progress on the development of a cryostat intended to improve upon the low-energy threshold (below 0.5 keV) of p-type point contact germanium gamma-ray spectrometers. Ultra-low energy thresholds are important in the detection of low-energy nuclear recoils, an event class relevant to both dark matter direct detection and measurement of coherent neutrino-nucleus scattering. The cryostat design, including a thermal and electrical-field model, is given. A prototype cryostat has been assembled and data acquired to evaluate its vacuum and thermal performance.

Dead layer on silicon p–i–n diode charged-particle detectors

A novel, multi-point contact high-purity germanium detector has been developed for applications in high-rate gamma environments. The planar detector was fabricated with seven point contacts, a high-voltage steering grid and bias electrode using amorphous germanium technology. We have characterized this detector and report herein on the depletion profile, leakage current, energy resolution, and charge-sharing behavior.

Cryostat for Ultra-Low-Energy Threshold Germanium Spectrometers

We present a working concept for Phase III of the Project 8 experiment, aiming to achieve a neutrino mass sensitivity of

A Multi-Point Contact HPGe Detector

2~\mathrm{eV}

Project 8 Phase III Design Concept

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Results from the Project 8 phase-1 cyclotron radiation emission spectroscopy detector

90~\%