Fabrication of framed beryllium windows by high rate physical vapor deposition processes

Beryllium windows are used in radiation generators and detectors such as x-ray tubes, counters, etc., because of the low atomic number of beryllium. In current practice, thin foils of beryllium >0.001-in. thickness and brazed or welded into a frame which is then attached to the apparatus. This presents the problems of procurement of the thin foil and damage to it during the joining process. In our technique, beryllium is evaporated onto a substrate such as copper to the desired thickness and the window is produced by dissolving the substrate with concentrated nitric acid in the window area after masking off the area which forms the frame. Thus, a framed window of the different shapes can be produced. The principal problem is porosity in the deposit below 0.002-in. thickness.