Further studies of electron avalanche gain in liquid argon

Abstract

Previously [1] we showed how small admixtures of xenon (Xe) stabilize electron avalanches in liquid Argon (LAr). In the present work, we have measured the positive charge carrier mobility in LAr with small admixtures of Xe to be 6.4 x 10 -3 cm 2 /Vsec, in approximate agreement with the mobility measured in pure LAr, and consistent with holes as charge carriers. We have measured the concentration of Xe actually dissolved in the liquid and compared the results with expectations based on the amount of Xe gas added to the LAr. We also have tested LAr doped with krypton to investigate the mechanism of avalanche stabilization.

Further studies of electron avalanche gain in liquid argon

“…By heating, this liquid sample is expanded to the gaseous state into a one-liter sampling bottle that can be shipped to an analysis laboratory. As indicated in our previous paper [1], a systematic decrease in the pulse height occurs over a run of several hours, which may be the result of the variation of impurtity concentrations in the sample with time.…”

“…The experimental setup has been previously described in [1], and schematics of the apparatus are shown in Figs. 1 and 2.…”

“…Previously, we implemented a mixing system using a pivoted alnico bar magnet inside the test vessel, rotated under the influence of an external driving magnet [1]. Subsequently, we have improved our mixing system and added a sampling system that extracts a ~10 ml sample of the LAr/Xe mixture for analysis.…”

“…In our previous paper [1] we presented measurements of the needle current versus voltage for avalanches in pure LAr, and suggested a model to explain the behavior. We have since repeated that test in LAr doped with ~25 ppm Xe for two different radioactive sources.…”

“…n our previous paper [1], we showed how small admixtures of Xe could stabilize electron avalanches in liquid argon (LAr). The avalanches were produced in a high electric field at the tip of a sharp needle, irradiated by 60 keV photons from an 241 Am source.…”