202 Prof. E. Rutherford on the Charge 



polonium, were interchanged. For example, with screens 

 of aluminium and cardboard, the current was greater when 

 the aluminium was uppermost. Similar results were obtained 

 with other materials. These results indicate that different 

 amounts of secondary radiations — probably in the form of 

 the slow-speed electrons in question — were produced at the 

 surface of the matter through which the rays passed. 



Charge carried by the ft Rays. 



It is of importance to determine the total number of ft 

 particles emitted from one gram of radium in radioactive 

 equilibrium, as, theoretically, it is to be expected that this 

 number should bear a definite relation to the total number of 

 a. particles expelled. Xow radium in radioactive equilibrium 

 contains four substances, viz., radium itself, the emanation, 

 radium A, and radium C, which emit a particles. On the 

 other hand, ft particles are only expelled from one product, 

 radium C. These substances are successive products of radium, 

 and, when equilibrium is reached, the same number of atoms 

 of each break up per second. If the disintegration of the 

 atom of each product is accompanied by the expulsion of one 

 a. particle and the case of radium C also of one ft particle, the 

 number of be. particles emitted from radium in radioactive 

 equilibrium will be four times the number of ft particles. The 

 number of ft particles from radium in equilibrium will thus 

 be equal to the number of a particles expelled at its minimum 

 activity, when the emanation and its further products are 

 absent. 



Some experiments have been made by Wien * to deter- 

 mine the number of ft particles expelled from a known 

 quantity of radium. About -I milligrams of radium bromide 

 were enclosed in a platinum cylinder, which was insulated in 

 a larger tube, and the air exhausted. The platinum cylinder 

 was found to gain a positive charge, since the ft particles, 

 some of which were projected through the cylinder, carried 

 with them a negative charge. The rate of escape of electricity 

 from the platinum cylinder corresponded to 2*91 x 10 -12 

 ampere. If each ft particle carries the observed ionic charge 

 o£ 1*13 x 10~ iy j this corresponds 10 an escape of 2*66 xlO 7 

 ft particles per second. From one gram of radium, the corre- 

 sponding number would be l'Mx 10 10 . 



It is known from experiments upon the absorption of the 

 ft rays from radium that some of the ft particles are easily 

 absorbed in passing through a small thickness of matter. 

 The above estimate is for this reason far too small. 

 * Wien, Physih. Zeit. iv. p. 624 (1903). 



