Spatial resolution properties of krypton-based mixtures using a 100 μm thick Gas Electron Multiplier

A gaseous imaging detector based on a cascade of two non-standard gas electron multipliers (100 mu m thick GEM) was operated in five different krypton-based mixtures and the achievable position resolution was determined. The micropattern gaseous detector (MPGD) has an active area of 10 x 10 cm(2). The GEM foils are twice as thick as a standard GEM, being more robust to electric discharges and less prone to sparking-caused damage. Krypton, being the noble gas with the lowest value of intrinsic position resolution in the range 14-34 keV, is a good candidate for imaging applications based on gaseous detectors. Our measurements have confirmed that krypton-CO2 mixtures showed an improvement in position resolution above 18 keV and up to 30 keV relatively to Ar-CO2 mixtures. The MTF value at 10% in the energy range 22-24 keV was evaluated, being 0.5876(342)1p/cm for Ar-CO2 (70:30) and a maximum of 3.2702(15) 1p/cm for the Kr-CO2 (90:10) mixture.