Polonium, Radium, and Radioactinium. 113 



The results obtained with ionium raised the question 

 whether this y-radiation is emitted by the disintegrating 

 atoms themselves, i. e. by the ionium, or by the thorium with 

 which it was mixed and from which it could not be separated. 

 Had the separation of thorium from ionium been possible, 

 this question would not have been a difficult one to answer, 

 but, as is well known, this cannot be done. To attack this 

 problem therefore, and to extend our knowledge of the 

 nature of the y-rays excited by the a-rays, we have continued 

 our work by investigating the y-rays emitted by polonium, 

 by the element radium itself, and by radioactinium. 



The fixe bodies we have investigated, viz. ionium, radio- 

 thorium, polonium, radium, and radioactinium, expel, in 

 addition to their a-rays, a small quantity of y-radiation. It 

 seems probable therefore that all a-ray bodies, when com- 

 pletely freed from all products and impurities emitting 

 /3- and y-rays, emit a measurable quantity of y-radiation, 

 provided the quantity of material under investigation is 

 sufficiently great. In the y-ray electroscope used by us, 

 which is a large one of the ordinary type with a very thin 

 window through which the rays pass, a quantity of about 

 1 milligramme of radium, or a quantity of another body, 

 expelling per second the same number of a-particles, is 

 necessary to obtain measurable effects. 



We found that the /3- radiation from ionium under our 

 experimental conditions was only about 10 per cent, in 

 intensity of the y-radiation, and a result of a similar nature 

 has been found with polonium. These a-ray bodies emit, 

 therefore, a very small amount of /3-radiation. Ihere are 

 other a-ray bodies, however, such as radium, thorium X, 

 and radioactinium, which emit considerable quantities of 

 ^-radiation. An investigation of the y-rays of one of these, 

 for instance radium, is therefore likely to show that it emits 

 y-rays corresponding to its /3-rays, as well as y-rays produced 

 by the a- rays. 



The great difficulty in this research has been to obtain a 

 sufficiently large quantity of polonium. By the kindness of 

 Professor Rutherford the strongest source of polonium 

 available in the laboratory was obtained, but the intensity 

 of the y-rays was disappointingly small. For this reason 

 we were unable to obtain, either in accuracy or in detail, the 

 results we hoped for when the work was commenced, and 

 for which the methods described in this paper were worked 

 out. 



Phil. Mag. S. 6. Vol. 27. No. 157. Jan. 191-4. I 



