﻿Disintegration of Elements by a Particles. 



423 



The Ranges of the H Particles. 



In the experiments described in our previous paper only 

 two elements, nitrogen and aluminium, were investigated 

 in any detail. The other elements were examined in a 

 qualitative manner, but it was shown that the ranges of 

 the liberated H particles were in every case greater than 

 40 cm. of air. The ranges of the particles from these 

 elements — viz. boron, fluorine, sodium, and phosphorus — 

 have now been determined more accurately. 



Attention has been drawn to the remarkable fact that the 

 H particles liberated from aluminium appeared not only in 

 the direction of the incident ot particles but also in the reverse 

 direction. The number of particles emitted in the backward 

 direction was of the same order of magnitude as for the 

 forward, but the maximum range in the backward direction 

 was smaller, being 67 cm. as against the 90 cm. range of the 

 forward particles, for a particles of 7 cm. range. Some 

 experiments with nitrogen showed that the number of 

 H particles emitted in the backward direction was very 

 small at absorptions of more than 18 cm. of air. 



We have repeated these experiments and extended them 

 to include the other elements boron, fluorine, sodium, and 

 phosphorus, with the result that we find that in every case 

 the H particles emitted on disintegration of the nucleus 

 escape in all directions, the maximum range in the backward 

 beino- less than in the forward direction. 



Fig. 2. 



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The experimental arrangement for the measurement of 

 the ranges of the forward particles was the same as that 

 described in our previous paper. The apparatus used in 

 the investigation of the particles in the reverse direction 

 differed from this in the arrangement of the source, and is 

 shown in the diagram (fig. 2). 



The source of a particles was carried on a rod passing with 

 a sliding fit through a stopper which fitted tightly into the 



