A Drift Multiwire Proportional Counter for Cosmic Soft X-Ray Imaging

Multiwire proportional counters with 1 ¿m polypropylene windows, of dimensions 75 mm × 75 mm and 100 mm × 100 mm, have been built to map soft cosmic X-rays. The counters are constructed with a large drift region which allows us to use the center-of-gravity technique to improve the counter´s efficiency and position resolution. Using 330 Torr of propane as the gas fill and an anode plane composed of 20 ¿m diameter, gold-plated tungsten wire spaced 1 mm apart, we have achieved a position resolution of better than 280 ¿m (FWHM) in two orthogonal directions at an X-ray energy of 0.94 keV.