Studies of Electron Avalanche Behavior in Liquid Argon

TL;DR

This study investigates electron avalanche behavior in liquid argon, examining how voltage, pressure, radiation, and additives like xenon influence stability and signal characteristics in high electric fields.

Contribution

It demonstrates that small xenon additives stabilize electron avalanches in liquid argon, providing insights into optimizing detector performance.

Findings

Xenon stabilizes avalanche behavior even at low concentrations

Pure liquid argon exhibits erratic avalanche behavior

Different gamma-ray energies produce similar spectra and signals

Abstract

Electron avalanching in liquid argon is being studied as a function of voltage, pressure, radiation intensity, and the concentrations of certain additives, especially xenon. The avalanches produced in an intense electric field at the tip of a tungsten needle are initiated by ionization from a moveable americium (241Am) gamma ray source. Photons from xenon excimers are detected as photomultiplier signals in coincidence with the current pulse from the needle. In pure liquid argon the avalanche behavior is erratic, but the addition of even a small amount of xenon (>100ppm) stabilizes the performance. Similar attempts with neon (30%) as an additive to argon have been unsuccessful. Tests with higher energy gamma rays (57Co) yield spectra and other performance characteristics quite similar to those using the 241Am source. Two types of signal pulses are commonly observed: a set of pulses that are sensitive to ambient pressure, and a set of somewhat smaller pulses that are not pressure dependent.