A Test for Possible X-ray Phosphorescence

IN examining photographs of the ray tracks produced in air, C. T. R. Wilson (Proc. Roy. Soc. A, vol. 104, p. 1, 1923) found that two tracks which were undoubtedly pairs were not alike: one was sharp and the other was a diffuse track; that is, pairs exist of which the two components have been ejected with an appreciable time interval. He roughly estimates this time interval to be of the order of 0.001 of a second. The first track he attributed to the photoelectron ejected by the primary X-ray, and the second track to an effect of the resulting fluorescent radiation. It was decided to search by a more direct method for the existence of such phosphorescence in the secondary X-rays from solid radiators.