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XXVIII. The Magnetic Deflexion of the Recoil Stream from 

 Radium A. By H. P. Walmsley, M.Sc, and W. 

 Makower, M.A., D-.Sc.* 



[Plate V. fig.l.] 

 TT^HE deflexions suffered in an electric and a magnetic 

 A field by the recoil stream of radium B produced by 

 the disintegration o£ radium A have been studied by Russ 

 and Makowerf and by Makower and Evans i. It was shown 

 that the atomic mass of radium B has approximately the 

 value 214 predicted by radioactive theory, and that each 

 particle in the recoil stream carries one positive charge. It 

 is of importance to repeat these experiments with greater 

 accuracy in order to determine the atomic mass of radium B, 

 and it is also of interest to find out how nearly the velocity 

 of the particles in the recoil stream is in agreement with 

 that to be predicted from a simple application of the law of 

 the conservation of momentum. Experiments on the mag- 

 netic deflexion of the recoil stream have been completed and 

 will be described, but the investigation of the electric 

 deflexion has unfortunately had to be postponed. 



When an atom of mass M disintegrates and emits an 

 a particle of mass m with a velocity v, the atom recoils with 

 a velocity V given by the equation 



(K-m)Y = mv. ...... (1) 



If the recoil stream and the a. rays pass through a magnetic 

 field of strength H, the radii of curvature p r and p a are 



respectively - — tg— - — and -^tt~, smce the recoil particles 



carry only one charge, whereas the a rays carry two. If. 

 therefore, the recoil stream and the « rays pass through the 

 same magnetic field, the radius of curvature of the former 



Fig. 1. 



I 



should be exactly double that of the latter. Using a line 

 source 0, a slit S, and a screen P placed perpendicular to the 

 line OS (fig. 1), the particles passing through the magnetic 



* Communicated by the Authors. 



t Russ and Makower, Phil. Mag-. Nov. L910. 



j Makower and Evans. Phil. Mag. Nov. 1910. 



