124 Dr. Russell and Mr. Chad wick on the y Rays of 



tr between 100 and 150. The amount of the intermediate 



type was about 1 div. per min. and ~ about 6. The hardest 



type gave about 3 div. per min, and gave — about *09 

 or -10. D 



By comparison with the radiations from other bodies, and 

 from the proportion of the different types, it would appear 

 that the two harder types are connected with the /3-radiation 

 while the softest type is due to a- rays. It is of course 

 possible that the intermediate type is also due to a-rays. 



Radioactinium. 



An examination has also been made of the radiations of 

 radioactinium. Halm and Meitner* showed that, besides 

 a-rays, the body emitted soft /8-rays, and a radiation which 

 was either a hard /3-radiation or a soft 7-radiation. An 

 actinium preparation was taken and its 7-radiation was found 

 to be about 23 div. per min. The radioactinium was separated 

 from this by chemical operations and its radiations examined. 

 We found that besides the soft /3-rays described by Halm 

 and Meitner, there was a 7-radiation of about 5*5 div. per min. 

 This 7-radiation was found to consist of two types, the 

 absorption coefficients of which were only approximately 

 determined. The measurements showed that these types 

 were very slightly harder than the two hard types emitted 



by ionium, the values of ycm.)" 1 being about 8 and 0*1. 



During this investigation we thought we had succeeded 

 in showing that radioactinium is complex, and in a letter to 

 ' Nature ' of 26th December, 1912, we stated that radio- 

 actinium consists of two products, the second of which has 

 a half value period of about 12 hours. Subsequent work 

 showed that the actinium preparation we had been using 

 contained a small amount of either mesothorium or radio- 

 thorium. This fact, and also the nature of the chemical 

 properties, suggested that the new product was really thorium 

 B, although the tests for thorium emanation indicated that 

 the amount of the contamination with thorium products was 

 not sufficient to vitiate the results. However, as both of us 

 are leaving Manchester, and as neither of us will have an 

 opportunity of continuing the work for some time, we think 

 it is better to withdraw our statement of the complex nature 

 of radioactinium. 



* Hahn & Meitner, Phys. Zeit. vol. ix. p. 697 (1908). 



