﻿Disintegration of Elements by u Particles. 



419 



The distance from the centre of the source to the farther 

 edge of the slit was 2*95 cm. The carrier of the source and 

 slit was placed in a rectangular brass box between the poles 

 of an electromagnet, the field being perpendicular to the 

 length of the slit. A current of dry oxygen was circulated 

 through the box during the experiment. 



Fig. 1. 



If 



4- 



vS 1 



3^ 



An extension piece L, projecting 1*7 cm. beyond the edge 

 of the slit, was fixed to the carrier in order to increase the 

 amount of deflexion of the particles issuing from the slit. 

 In the end of the box was a hole 1 cm. wide and 2 cm. long 

 covered with a sheet of mica of 3*62 cm. stopping-power. 

 The ZnS screen was fixed on the face of the box, leaving a 

 slot of 1 mm. depth in which absorbing screens could be 

 inserted. 



The source H was a brass disk of 1*2 cm. diameter coated 

 with the active deposit of radium. Its initial 7-ray activity 

 was usually equivalent to about 40 mgm. Ra. 



The materia], the particles from which were to be investi- 

 gated, was laid directly on the source if in the form of foil, 

 or if in the form of powder dusted over its face. 



The experiment consists in obtaining an estimate of the 

 deflexion of the particles falling on the screen by observing 

 the effect of a magnetic field on the number of scintillations 

 near the line E, the edge of the undeflected beam of particles. 

 The position of the microscope was fixed in the following- 

 way : — After placing the source of a rays in position, 

 hydrogen was passed through the box. The u rays could 

 then strike the ZnS screen, and the edge E of the beam was 

 clearlv defined. The microscope was adjusted so that the 



2 E 2 



