Simultaneous high resolution meausurement of phonons and ionization created by particle interactions in a 60 g germanium crystal at 25 mK

We demonstrate simultaneous high energy resolution (rms≊800 eV) measurements of ionization and phonons created by particle interactions in a semiconductor crystal of macroscopic size (60 g germanium) at 25 mK. We present first studies of charge collection at biases below 1 V/cm, and find that, contrary to commonly held opinion, the full recoil energy of particle interactions is recovered as phonons when charge trapping is negligible. We also report an unanticipated correlation between charge collection and phonon energy at very low bias, and discuss this effect in terms of charge trapping

Measurement of ionization and phonon production by nuclear recoils in a 60 g crystal of germanium at 25 mK

We report on the first measurement of the absolute phonon energy and the amount of ionization produced by the recoil of nuclei and electrons in a 60 g germanium cyrstal at a temperature of ≊25 mK. We find good agreement between our results and previous measurements of ionization yield from nuclear recoils in germanium. Our device achieves 10:1 discrimination between neutrons and photons in the few keV energy range, demonstrating the feasibility of this technique for large reductions of background in searches for direct interactions of weakly interacting massive particle dark matter

The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) Mission Concept

The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is designed to identify and characterize gamma rays from extreme explosions and accelerators. The main science themes include: supermassive black holes and their connections to neutrinos and cosmic rays; binary neutron star mergers and the relativistic jets they produce; cosmic ray particle acceleration sources including Galactic supernovae; and continuous monitoring of other astrophysical events and sources over the full sky in this important energy range. AMEGO-X will probe the medium energy gamma-ray band using a single instrument with sensitivity up to an order of magnitude greater than previous telescopes in the energy range 100 keV to 1 GeV that can be only realized in space. During its three-year baseline mission, AMEGO-X will observe nearly the entire sky every two orbits, building up a sensitive all-sky map of gamma-ray sources and emission. AMEGO-X was submitted in the recent 2021 NASA MIDEX Announcement of Opportunity.Comment: 23 pages, 16 figures, Published Journal of Astronomical Telescopes, Instruments, and System

Gamma Ray Source Localization for Time Projection Chamber Telescopes Using Convolutional Neural Networks

Diverse phenomena such as positron annihilation in the Milky Way, merging binary neutron stars, and dark matter can be better understood by studying their gamma ray emission. Despite their importance, MeV gamma rays have been poorly explored at sensitivities that would allow for deeper insight into the nature of the gamma emitting objects. In response, a liquid argon time projection chamber (TPC) gamma ray instrument concept called GammaTPC has been proposed and promises exploration of the entire sky with a large field of view, large effective area, and high polarization sensitivity. Optimizing the pointing capability of this instrument is crucial and can be accomplished by leveraging convolutional neural networks to reconstruct electron recoil paths from Compton scattering events within the detector. In this investigation, we develop a machine learning model architecture to accommodate a large data set of high fidelity simulated electron tracks and reconstruct paths. We create two model architectures: one to predict the electron recoil track origin and one for the initial scattering direction. We find that these models predict the true origin and direction with extremely high accuracy, thereby optimizing the observatory’s estimates of the sky location of gamma ray sources

Low noise front end electronics for dilution refrigerator experiments

We have developed low noise voltage and low noise charge sensitive preamplifiers for use in dilution refrigerator experiments. The amplifiers use a JFET at 140K as the front end. Each JEET dissipates about 7 mW on the 4K heat sink. The flat noise of the voltage amplifier is 0.9 nV/Hz1/2, with the 1/f knee below 100 Hz. The charge amplifier noise is 500 eV with a total input capacitance of approximately 90 pF

Measurement of Electron Phonon Decoupling Time in Neutron-Transmutation Doped Germanium at 20 mK

We have studied the electron-phonon decoupling in Neutron-Transmutation Doped (NTD) Germanium thermistors below 50 mK, and measured a characteristic time constant of this phenomenon. We will discuss how our decoupling model accounts for observed non-linearities in I–V characteristics of NTD Ge and for the time structure of phonon pulses detected in a Ge crystal operated at 20 mK