X-ray position detection at 22μm FWHM with a gas proportional chamber

Measurements have been made of x-ray position resolution in proportional chambers using xenon/CO₂, argon/ CO₂, and hydrocarbon gases. The use of several atmospheres of gas pressure to reduce photoelectron range, and a very low noise position readout, have made it possible to observe more clearly the behavior of position resolution with anode avalanche size. Resolution begins to degrade above a critical avalanche size, whose value varies inversely with gas pressure. For 5.4 keV and 8 keV x-rays in 5 atm. Xe/10% CO₂, a resolution of 22 μm FWHM is measured, provided the anode avalanche is not greater than /spl I.itilde/ 10⁶ electrons.