An array of electrode plates are arranged in parallel and spaced apart relationship to define ionization cells in a channel within a housing that is occupied by high pressured gas. A broad beam of x-ray photons penetrates a window in the housing and produces ionization events that result in analog signals corresponding with photon energies and intensities. Conduction of the signals from the interior to the exterior of the detector housing is accomplished with a printed circuit board assembly that is sealed between the housing and its cover.