Abstract: A rugged scintillation detector uses a hermetically sealed window assembly welded or otherwise bonded to the detector housing. A method and apparatus useful in forming a reproducible hermetic seal between the glass and an annular metal retaining ring is described. The glass and ring are chosen so that the ring diameter is slightly larger than that of the glass at room temperature. A thin layer of frit at the interface ensures a very tight mechanical seal, and a surface layer of chromium oxide on the ring ensures a secure chemical bond. The assembly device uses pressure and counterpressure to uniformly and reproducibly assemble the glass window into the retainer ring at elevated temperatures.