SOFT X-RAY DETECTORS.

The relative quantum efficiencies of various photocathode materials were studied in the soft X-ray region. Using the monochromatic line of Al K sub alpha with Au, Al, Cr, CsI, NaCl, and MgF2 photocathodes, the angular dependence of the photoelectric yield was studied. These measurements were performed with the recently developed Spiraltron TM photon detector, a windowless electron multiplier characterized by high gain and a Gaussian gain distribution for single photonelectron inputs. The detector response to Cu target radiation, including the CuL sub alpha line, is compared to the flow proportional counter response. The location of the absorption edges for the photocathodes are determined and it is concluded that the photocathodes are useful only in spectral regions free of photocathode absorption edges. In addition to the Spiraltron photon detector, an MEM with a replacement photocathode was provided. This MEM can also be used as a photon detector in this spectral region when operated at near grazing incidence. Author