The form of X-ray photoelectron tracks in a capillary gas proportional counter

We have successfully detected images of tracks of photoelectrons from the 22 keV and 30 keV X-rays of ¹⁰⁹Cd and ²⁴¹Am, utilizing an optical imaging gas detector with a CCD camera. Most of the 30 keV photoelectrons have track lengths greater than 1 mm in xenon gas. The images of the tracks contain clusters of pixels, and the brightest of these clusters, for each track, were investigated in detail. It was found that the average shape of these clusters was oval-like and that the geometrical center differs from the point of maximum energy loss. These data have important implications for X-ray polarimetry