834 HANDBOOK OF PHOTOGRAPHY 



Radium Radiography. — In recent years the use of gamma rays from radium as a 

 means of visuaUzing subsurface faults has received increasing attention in cases where 

 the examined material is too thiek to be conveniently penetrated with X rays. 

 Gamma rays are similar in nature to X rays but are of much shorter wavelength than 

 the X rays used in general practice and are therefore able to pass through substances 

 opaque to the X ray. Figure 9 shows a gamma-ray exposure chart for steel. 



The apparatus necessary for gamma radiography is extremely simple and does not 

 require the space, trouble, or attention encountered in X radiography. A small 

 capsule container of radioactive material is held rigidly in front of the specimen to be 

 inspected and X-ray films in holders are fastened to the back of the specimen. After 

 the required time has passed, radium and films are removed. It will be found on 

 development of the film that the gamma rays passing through the specimen have 

 recorded, as with the X ray, conditions existing within the sample. 



The exposure chart given is applicable for practically any type of steel because 

 gamma radiography errors in exposure time generally amount to a small fraction of 

 the total. 



Bibliography 



Books: 



"X-ray Laboratory Manual," Eastman Kodak Co. 



"Handbook of Physics and Chemistry," Chemical Rubber Pub. 



Gezelius, R. a., and C. W. Bbiggs: "Radium for Industrial Radiography," Radium Chemical Co. 



CoMPTON and Allison: "X-ray in Theory and Experiment," Van Nostrand. 



Clark, G. L. : "Applied X-rays," McGraw. 



Terrill, H. M., and C. T. Urey: "X-ray Technology," Van Nostrand. 



PouLLiN, V. E.: "Engineering Radiography," G. Bell. 



Periodicals: 



Woods, R. C: Industrial X-ray Practice, Electronics, February, 1936. 



— : Radium Inspection of Metal Structures, Iron Age, July 16, 1936. 



: Details of Industrial X-ray Apparatus, Iron Age, Oct. 16, 1936. 



X-ray Protection, Nat. Bur. Standards, Handbook 15. 



