Originally published in Kgl. Dan-ske VidenshaherneN Selskab. Maihcmatisk-fysiske 



Meddeleher. 14, 5 (193G) 



4. THE ACTION OF NEUTRONS ON THE RARE 



EARTH ELEMENTS 



G. Hevesy and Hilde Levi 

 P'loni the Institute of Theoretical Physics, University of Copenhagen 



The action of neutrons on the rare earth elements can be followed uj) 

 in two ways : by investigating the radioactivity induced in these elements 

 under neutron bombardment, and by observing their absorbing power 

 for a beam of slow neutrons. In this paper both these lines of attack 

 will be discussed for the rare earth group and for yttrium and scandium. 



ARTIFICIAL RADIOACTIVITY OF THE RARE EARTH ELEMENTS 



The artificial radioactivity of some of the rare earth elements was 

 investigated by Amaldi, D'Agostino, Fermi, Pontecorvo, Rasetti 

 and Segre (1), others were investigated by ourselves (2) by Sugden (3) 

 by Marsh and Sugden (4) by McLennan and Rann (5) and by E. 

 RoNA (6). The neutrons used were produced by the action on beryllium 

 of the a -rays from radium emanation and were in many cases slowed 

 down by inserting layers of paraffin 10 — 20 cm thick in the path of 

 neutrons ; a Geiger— MItller counter was used to measure the activi- 

 ties obtained. 



Scandium 



A sample of scandium oxide prepared by Prof. Sterba-Bohm and 

 kindly presented to us by Prof. Honigschmid, who used the preparation 

 in determining the atomic weight of scandium, was activated for a few 

 days using an emanation-beryllium source of 200 — 300 MC. The oxid(> 

 was then dissolved in dilute hydrochloric acid and 100 — 150 mgm sodium 

 chloride as a carrier of ■^^K (cf. p. 48) and the same amount of calcium 

 oxide were added. The filtrate obtained after precipitation with carbon- 

 ate-free ammonia was treated with oxalic acid and the calcium oxalate- 

 formed was removed. The sodium chloride which had been added was 

 recovered, after the removal of the ammonium chloride content of 1 he 

 last filtrate, by evaporation and ignition. The activities of the three 



