THE ACTION OF NEUTRONS ON THE HARE EARTH ELEMENTS 



49 



10 days 



Fig. 1 



10 days 



^ a) Decay Curve of a Pure and an Impure Yttrium Preparation, 

 b) Samarium Decay Curves (the two days' period only; the weak period 



of 40 min is not visible;. 



cally and their separation is attended with very great difficulties. Figure 

 1 shows the decay of a pure preparation and of one containing some 

 dysprosium . 



Since yttrium has only one stable isotope, ^^Y, the artificial radio- 

 activity obtained from it is presumably due to the formation |^Y. We 

 find the intensity of the yttrium activity to be 0.005 times as large as that 

 of dysprosium, both preparations having been activated until saturation 

 was obtained in a paraffin block of 30x30x25 cm edge ; the neutron 

 source was placed on the top of the preparation which w^as covered by 

 a thin shield of paper. The ^-rays emitted by yttrium are absorbed 

 1() half of their initial value bv 0.6 mm Al. 



Lanthanum 



Marsh and Sugden (4) find 1.9 days as the half-life of lanthanum 

 and for the intensity of the /?-rays emitted, a value amounting to 35% 

 of that observed for the activity of praseodymium. As we find a value of 

 22 for the ratio of the radiation intensities of dysprosium and praseody- 

 mium, the lanthanum activity works oul at 2.0% of that of dysprosium. 



4 Tlcvcsy 



