Lexan coating to eliminate the UV sensitivity of soft x-ray proportional counters with a polypropylene window

Lexan coatings on polypropylene windows can eliminate the UV sensitivity of soft x-ray proportional counters. A method is described for coating thin polypropylene films by dipping into and withdrawing from a volatile solution containing Lexan. The x-ray absorption of a typical Lexan coating was only 7% at 44 A which is small compared to that of 2 microm of polypropylene. The Lexan coatings are stable against vacuum cycling in an environment of UV irradiation. As an external, far-UV filter up to wavelengths of 2400 A, Lexan-coated polypropylene is an interesting alternative to metallic films, particularly when large area, high x-ray transmission, and strength are important.