﻿422 Sir E. Rutherford and Dr. J. Chadwick on the 



weak source of the thorium active deposit obtained by ex- 

 posing a disk to thorium emanation. Hydrogen was passed 

 through the box, and sufficient absorbing screens were inserted 

 in front of the ZnS screen to cut out the 5 cm. a particles of 

 thorium G. The numbers of a particles falling on the screen 

 for — and + fields due to an exciting current of 6 amps, were 

 counted, and the ratio of these numbers was found to be 2'4. 

 Comparing this ratio with those found for the long-range 

 particles, we see that the value of mv/e for the latter is about 

 0'8 of that for a particles of 8'6 cm. range, i. e. about 

 3*4 x 10 5 e.m. units. The calculated value, assuming that 

 the particles are H nuclei and that their velocity is pro- 

 portional to the cube root of the range, is about 3*7 X 10 5 ,e.m. 

 units. Considering the difficulty of the experiments, the 

 agreement is satisfactory. 



Experiments on Phosphorus and Fluorine. 



Measurements similar to the above have also been made on 

 phosphorus and fluorine. 



In the case of phosphorus, a thin layer of red phosphorus 

 was dusted over the face of the source. The total absorption 

 in the path of the particles was about 35 cm. ; the range of 

 the particles under observation varied therefore from 35 cm. 

 to the maximum range of 65 cm., the average being about 

 45 cm. The ratio of the numbers of scintillations for — and 

 + fields due to current of 4 amps, was 2*0. 



In the case of fluorine finely powdered calcium fluoride was 

 dusted over the source. Previous experiments have shown 

 that no long-range particles are emitted from calcium. The 

 total absorption in the path of the particles was about 30 cm. 

 The maximum range of the particles from fluorine is approxi- 

 mately 65 cm., and the average range of the particles falling 

 on the screen was around 40 cm. The ratio of the numbers 

 of particles observed for — and ■+■ fields due to an exciting 

 current of 4 amperes was 2*5. 



It is clear from these results that, within the error of 

 experiment, the particles liberated from phosphorus and from 

 fluorine are bent in a magnetic field to approximately the 

 same extent as the particles from aluminium. We may 

 conclude, therefore, that these particles also are H nuclei 

 moving with high speed. 



We have not examined the particles from boron and 

 sodium in this way, but there seems no reason to doubt that 

 they also consist of H nuclei. 



