Ionization in Solid- and Grid-Walled Detectors

Energy deposition spectra produced in a grid-walled proportional counter are compared to spectra produced in a conventional solid-walled detector. The radiation sources studied include 60 Co gamma rays, filtered 250 kVp X rays and unfiltered 250 kVp and 65 kVp X rays. The solid wall is shown to produce significant distortion of the spectra for 60 Co gamma rays and filtered 250 kVp X rays but not for the unfiltered X rays. The size of the container housing the grid-walled detector was varied and the wall effect was found to decrease less rapidly with increasing distance between the detector and the wall than would be expected on the basis of geometric considerations.