[RUTHERFORD] PROPERTIES OF THE a RAYS FROM RADIUM 5 



The activity of radium C dies down with the time, falling to half 

 value in the first 60 minutes after removal. After two hours the 

 activity ia reduced to 15 per cent of the initial value. 



In order to produce a well marked photographic action, using a 

 narrow pencil of a rays at the distance of about 7 cms., required in 

 the experiments, it was necessary to employ an intensely active wire as 

 a source of radiation. For this purpose, a thin wire, about 1 cm. long, 

 was charged negatively to 800 volts in the presence of the accumulated 

 emanation from about 20 milligrams of radium bromide in solution. 

 The wire to be made active was the only negatively charged body 

 exposed in the presence of the emanation and, consequently, the active 

 deposit was concentrated upon it. In this way, the fine wire was made 

 extremely active and produced strong luminosit}' on a screen of zinc 

 sulphide or willemite brought near it. 



Magnsiic DefJcciion of the a Ray?. 



The method of determining the amount of deflection of the a rays 

 in a mao-netic field is shown in Ym. I. 



To Pump -< 



AeiTiVE: V^ire: 



Fiff. I. 



