A Cryogenic Apparatus with On-Line Purification System for Scintillation and Ionization Studies in Noble Liquids

Abstract

The scintillation and ionization properties of liquid argon, krypton and xenon have been investigated by means of a small laboratory apparatus. The setup consists of a cryogenic system which has the capability of cooling any liquid from ambient down to liquid nitrogen temperature and of a pulsed 10 to 100 kV electron gun used as excitation source of the liquids. By changing the electron beam intensity and the acceleration voltage, a total energy ranging from 1 MeV to 100 GeV per pulse can be deposited in the liquid (about a tenth of a liter). A forced circulation system allows continuous purification and recondensation of the evaporated gas. A description of the various purification methods, of the used materials and of the adopted cleaning procedure are given. The achieved degree of purity of liquid argon, krypton and xenon permitted an electron lifetime ≥ 200 μs corresponding to an oxygen equivalent contamination of less than 10 ppb. Measurements of the temperature uniformity of the liquid and its influence on the light scattering are presented. A scintillation yield in liquid xenon (at a wavelength of 175 nm) of 26×106 photons/GeV was measured.