Danysz and Duane — Electric Charges of a- and $-Rays. 295 



Art. XXYI. — On the Electric Charges of the a- and (S-Rays ; 

 by Jean Danysz and William Duane. 



This article contains a description of experiments designed 

 to measure the electric charges carried by the a- and /3-rays 

 from a given quantity of a radio-active substance. The experi- 

 ments were begun several years ago at the suggestion of 

 Madame Curie, but were discontinued pending the construction 

 of a satisfactory source of rays and the preparation of the 

 international standard of radium. 



A good source of rays should admit of easy comparison with 

 the radium standard, and should be so constructed that all the 

 rays produced emerge from it. Radium is not satisfactory 

 because the substance itself absorbs an imperfectly known frac- 

 tion of its own rays, and because it is not easy to determine 

 just how much emanation and active deposit there is in the 

 salt at every instant of time. The active deposit, radium ABC, 

 although perfect from the point of view of absorption, is not 

 convenient on account of its rapid rate of decay, and also 

 because it is not easy to deposit very large quantities on a small 

 surface even in a strong electric field. We have chosen the 

 emanation of radium with the active deposit in equilibrium 

 with it (radium ABC) as our source of rays for the following 

 reasons : (a) it is possible to measure a quantity of emanation in 

 terms of the amount actually present in the international stand- 

 ard of radium with considerable accuracy by means of the 7-ray 

 methods, (b) the rate of decay of the emanation with the time 

 is very accurately known, (c) the rate of decay is so slow that 

 a given quantity can be used for a long time before it becomes 

 too small, (d) the masses of the active substances are so small 

 that the a- and /3-rays are not* appreciably absorbed by them, 

 and (e) a large quantity of emanation and active deposit can be 

 compressed into a very small space, thus producing very nearly 

 a point source of intense radiation. 



The emanation being a gas must be confined in something, 

 and we have employed small spheres of glass with very thin 

 walls. * After its preparation (for method of blowing spheres 

 see references) the little sphere is sealed on to the tubes 

 employed in the purification of the emanation, and a little 

 bubble of emanation is pushed by mercury into the upper part 

 of the sphere. The bubbles have volumes of about -5 mm3 , and 

 the spheres about 14 mm3 , so that a bubble is flattened out 

 between a surface of glass and one of mercury, each of which 



* Such point sources of rays have "been employed by Duane and Lind 

 (Comptes rendus, July, 1911, Radium, 1912, and Sitz. der Akad. Wien, 

 Dec, 1911). 



