72 ADVEXTTRES IX RADIOISOTOPE RESEARCH 



the europium concentration, we added 2% of europium oxide to a puie 

 gadolinium preparation denoted as standard sample in Table 7 and 

 compared the activity of the latter with that of the gadolinium prepara- 

 tions of unknown europium content. The results are seen from Table 7. 



Table 7. — Activity of Different Gadolinium Preparations 

 (The sample labelled "Standard" is the GdjOa to wliich 2% 'EiuO^ was 

 added: samples 1 — 4 represent progressiv stages in the purification process 



can-ied out by Prof. Rolla) 



That, in spite of the large amount of radium and emanation used, the 

 activities measured were not stronger is partly due to the high absorbing 

 power of gadolinium, which reduces the density of thermal neutrons. 

 This effect is especially marked on account of the fact that the thermal 

 neutrons diffuse and are likely to pass through the preparation several 

 times. The latter effect can be best estimated by comparing the activity 

 of pure europium oxide with that obtained when this material is 

 embedded in gadolinium oxide. We activated simultaneously 200 

 mgm of europium oxide and 200 mgm of gadolinium oxide containing 

 2% of europium. If gadolinium absorbed to the same extent as 

 europium, the first named preparation should be 50 times more active 

 than the last mentioned one. Actually we find the ratio to be 200 from 

 which it follows that the presence of gadolinium in our preparations 

 reduced the activity of europium to y^ of the value which would have 

 been obtained if the same amount of europium oxide had been subject- 

 ed to irradiation. 



Suniinary 



The irradiation of liafiiium with noutrons has been shown <o produce a radio- 

 activity with a half-hfe of 55 ± 7 days which may be ascribed to ^^g^lf- The 

 intensity of the fi-rays emitted is reduced to half of its initial value by an alumi- 

 nium foil having a weight of 16 mgm/cm^. 



Scandium, ^JSc, was found to decay with a half-life of 90 ± 5 days. The half 

 ^•alue thickness for the absorption in aluminium of the /?-rays from this element 

 was found to be 13 mgm/cm^. 



The euiopium content of gadolinium oxide samples prepared by Professor 

 LuiGi RoLLA was determined by making use of the artificial radioactivity- pro- 

 duced imder the act ion of neutrons on the europium present in his samples. 



