Compressed xenon gas near its critical point as an ionization medium

The authors report results obtained from a dual gridded ionization chamber filled with highly purified gaseous xenon operating near its critical point where the density, ρ_c=1.09 g/cm³, approaches that of the liquid phase. The data obtained suggest that xenon near its critical point is an important addition to the presently available high-resolution radiation detector media. Both the ability to drift ionization electrons over large distances without attenuation and stability with time have been demonstrated. The energy resolution of the 976-keV K-conversion electron peak of ²⁰⁷Bi was measured to be 20 keV FWHM in 1.4 g/cm³ (62 atm) of xenon, independent of the distance over which the charge drifts. These findings indicate that attachment to electronegative impurities is not a problem. An additional effect was observed as the density of the xenon gas was lowered from 1.4 to 0.5 g/cm³: the energy resolution improved without an increase in the average charge collected