66 



ADVEXTURES IX RADIOISOTOPE RESEARCH 



tain some information on the then not entirely elucidated nature of the 

 natural radioactivity of potassium. We bombarded a few grams of very 

 pure scandium oxide prepared by Prof. Sterba-Bohm and used by Prof. 

 HoNiGSCHMiDT in his work on the atomic weight of scandium. After 

 neutron bombardment the scandium oxide was dissolved in dilute hydro- 

 chloric acid and 100 — 150 mgm of sodium chloride as a carrier of ^^K 

 and the same amount of calcium oxide was added. The filtrate obtained 

 after precipitation with carbonate-free ammonia was treated with oxalic 



^ 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 36 40 42 days 



Fig. 2. Dec;iy Curve of the Potassium Precipitate. 



acid and the calcium oxalate formed was removed. The sodium chloride 

 which had been added to the solution of the scandium chloride compound 

 was recovered after the removal of the ammonium chloride content of 

 the last filtrate by evaporation. The activities of the three fractions, 

 namely scandium oxide, sodium chloride, and calcium oxalate, were 

 then determined. Only the two first preparations mentioned were found 

 to be active. The activity of the scandium oxide decayed very slowly 

 while the various sodium chloride fractions obtained in different ex- 

 periments lost half of their slight activity within 10 and 18 hours. We had 

 just finished the experiment mentioned when a note was published by 

 Fermi and his collaborators (1) concerning the action of neutrons on 

 potassium. They found that potassium captured neutrons by giving 

 birth to a potassium isotope decaying with a half- life of 16 hours. The 

 values found by us for the period of the slight activity of different 

 potassium preparations obtained from irradiated scandium showed a 

 half- life between 10 and 18 hours; we thought it justifiable, therefore, 

 to identify the element found by us with that found by Fermi and his 

 collaborators. The initial activities measured amounted usually to about 

 10 counts/min. In one case, through the courtesy of the Medical Radi- 

 um Station and Dr. J. C. Jacobsen, we obtained an unusually strong 

 neutron source containing 600 millicuries radium-emanation. The decay 

 curve obtained for potassium 42 in this experiment is seen from Fig. 2. 



