﻿82 Dr. 0. Halm on some Properties 



Conclusions. 



The above analysis of the decay curves of the active deposit 

 from radium clearly establishes the following points: — 



(1) That, within the limits of experimental error, the expe- 

 rimental decay curves agree with the theoretical decay curves, 

 calculated on the assumptions that the three products A, B, 

 and C are successive, and that their periods are respectively 

 3, 26, and 19 minutes. 



(2) That radium B (as Schmidt observed) emits ft rays of 

 less penetrating power than those from radium C; and that 

 on this account the /3-ray decay curves are unsatisfactory for 

 the purposes of analysis. 



(3) That these /3 rays from radium B completely explain the 

 divergence which Rutherford found between the experimental 

 and theoretical /3-ray curves. 



In conclusion, I take pleasure in expressing my indebtedness 

 to Professor Rutherford for his continued guidance throughout 

 this work. 



, ^N9 Macdonald Physics Building, 

 *A McGill University, Montreal. 



^ J May 1, 1906. 



XIII. On some Properties of the a Rays of Radio- 

 tliorium. (II.) By 0. Hahn, Ph.D. 



THE first communication on this subject (Phil. Mag. June 

 1906) dealt with the properties of the a. particles emitted 

 by the active deposit of thorium. It was shown that the active 

 deposit consists besides thorium A of two «-ray products-, 

 thorium B and thorium C, which have quite distinct ionization 

 ranges in air and other substances. 



Tbe present paper deals with the ionization ranges of the 

 other a-ray products of thorium, namely radiothorium, thorium 

 X, and the emanation. The method used, with the excep- 

 tion of the experiments with the thorium emanation, was 

 very similar to that employed by Bragg and Kleemanf for 

 the different radium products. The apparatus, however, had 

 to be slightly altered for reasons described below. 



In the case of thorium some special difficulties are at once 

 encountered, as there are two essential conditions to be fulfilled 

 in order to obtain well-defined ionization curves : — 



(1) The material to be investigated has to be present in a 

 very thin layer, so as to allow all the a particles to escape 



* Communicated by Professor E. Rutherford, F.R.S. 



t Bragg & Kleeman, Phil. Mag. Dec. 1904 ; and Sept. 1905. 



