The photo-electric properties of some metals in the soft X-ray region

In a paper by Richardson and Robertson dealing with the absolute values of the efficiencies of various substances as soft X-ray producers, the values obtained for carbon, iron, nickel and tungsten differ considerably from those obtained earlier by Richardson and Chalklin. It was suggested that the difference between the two sets of results might be due to the fact that Richardson and Chalklin used a copper photo-electric detector, while Richardson and Robertson used a nickel one. The photo-electric detector consists of a metal disc (the actual detector) surrounded by a cylinder. There is an accelerating voltage (approximately 100 volts) between the disc and cylinder, so that photo-electrons emitted from the disc are drawn to the cylinder. It was thought that the difference in the metals used for the photo-electric disc might account or the difference in the results. A quartz tube, of similar design to that used by Richardson and Robertson, used to investigate the suggested cause of difference between the results discussed above. The apparatus is shown in the diagrams below (figs. 1, fig and 3).