Polonium, Radium, and Radioactinium. 121 



Experiments with other metals were not carried out owing 

 to the difficulty o£ measuring the small effects to be obtained 

 with the quantity of polonium at our disposal. Such ex- 

 periments can be most conveniently carried out with an 

 a-ray body which can be obtained in considerable quantity, 

 such as radium C. The experiments with polonium show 

 that an excited radiation can be produced by a-rays in at 

 least one metal, a phenomenon that has already been found 

 with radium C. In this connexion it may be mentioned 

 that recently Rutherford and Richardson*, using a source 

 of radium C on a nickel plate, found that the a-rays produced 

 in nickel a soft 7-radiation probably belonging to series K. 



The y-rays of Radium. 



Hahn and Meitnerf found that radium, completely freed 

 from all its short- and long-lived products, emitted a radia- 

 tion of a very soft type having a coefficient of absorption //, 

 in aluminium of about 312 (cm.) -1 . This result was con- 

 firmed by Kolowrat J, who found a value of //, of 200 (cm.) -1 . 

 This radiation is a /3- and not a 7-radiation, for it is capable 

 of being deflected by a magnetic field, and has been shown 

 to consist of two groups of homogeneous rays expelled with 

 velocities 0*52 and 0*65 of the velocity of light. The amount 

 of this radiation measured in the ordinary way was about 

 2 per cent, of the total /3-radiation of radium in equilibrium 

 with its products. So far, however, no one has carried out 

 an investigation to determine if a y-radiation accompanies 

 this /3-radiation. 



Several investigators, however, have pointed out that if a 

 radium solution, from which the radium D, E, and F have 

 been removed, be evaporated slowly to dryness in such a way 

 that all the emanation is expelled and all the short-lived 

 products have time to decay, the intensity of the 7-radiation 

 is about 2 per cent, of the initial activity, if the rays are 

 measured through a sufficient thickness of material to absorb 

 the /3-rays completely. It was natural in the early experi- 

 ments to attribute this radiation to the presence of some 

 radium C which had not been removed by the methods em- 

 ployed. In the light of subsequent work, it is possible that 

 this radiation, or at least a part of it, is emitted by the 

 radium atoms themselves, and is not to be ascribed to radium 

 B and G. 



* Rutherford & Richardson, Phil. Mao-, vol. xxv. p. 722. 

 t Hahn k Meitner, Phys. Zeit. vol. x.'p. 741 (1909). 

 t Kolowrat, Le Radium, vol. vii. p. 269 (1910). 



