Experimental Radiography utilising the Gamma Rays of Radium

A great deal of work has been carried out in the examinations of metals by means of X rays, but so far only a little attention has been paid to the possibilities of using gamma rays for this purpose. Whilst very successful results have been obtained for thicknesses of steel and iron up to about 3½ in., it has not, so far, been practicable to attempt X-ray radiography for thicknesses greater than this. It is beyond this region that gamma rays should prove particularly useful. It is not intended in this paper to go deeply into the principles underlying the use of gamma rays for detecting flaws in castings or welds. The object is to point out the possibilities and advantages of gamma rays, and to show a few radiograms of different subjects taken by this method. There appear to be only two satisfactory means of obtaining gamma rays—either from a radium salt or from radium emanation. To obtain a sufficiently large quantity of radon necessitates a very large quantity of radium—perhaps as much as a gramme—with suitable collecting apparatus and a skilled physicist to extract the radon. Radium salts, on the other hand, can be obtained in sealed platinum containers—thus obviating any difficulty of the preparation of the source of gamma rays. Furthermore, when using radon, the fact must be taken into account that the strength of the radiation decreases with time, whilst the radiation from a radium salt is constant in value.