[RUTnERFORD] PROPERTIES OF THE a RAYS FROM RADIUM 



Velociiy of the a Bays from other Products. 



11 



Knowing the velocity of the a particle expelled from radium C, 

 the velocity of the oc particle emitted from the other radioactive pro- 

 ducts can at once be deduced, provided the maximum range of its 

 ionization in air is kno^vn. 



This velocity can be determined from the data already given of tho 

 decrease of the velocity of the a particle in passing through screens 

 of aluminium foil. The ionizing action of the oc rays ceases after 

 passing through 12.5 layers of foil, which is equivalent to a thickness 

 of 6.7 cms. of air. Each layer of foil corresponds to a depth of 0.54 

 cms. of air. The velocity, for example, of the rays from radium itself, 

 which have a range of 3 cms. in air, that is, which would be stopped 

 bv 5.5 thiclmesses of foil, corresponds to the velocity of the rays from 

 radium C, which have traversed 12.5 — 5.5 = 7 layers. For conveni- 

 ence, the velocities of the a particles from different products, which have 

 ranges in air from 1 to 6.7 cms., are given in terms of V^ the velocity 

 of the a particle from radium C. 



The following table shows the maximum ranges of the a particle 

 for the various products of radium experimentally observed ]3y Bragg. 

 The corresponding initial velocity of projection is also shown: — 



