ARTIFICIAL ACTIVITY OF HAFNIT'M AND SOME OTHEK ELEMENTS (if) 



We measured also tlic absorption in aluminiuui of the /?-rays emitted 

 by hafnium. The values obtained ai(> seen from Table 3. 



Tablk ."}. — Absorption in Aluminium of the j6-k.\vs Emittku 



BY Hafniltm 



Thickness of tlie Al-£oil j Uou uts/miii. 





 1 1 mgm/cm^ 

 16.5 mgm/cm^ 



1.5.8 



10.2 



7.4 



(half value thickness : 16 i 1 mgm/cm^). 



From the figures in Table 3 follows that an aluminium layer of 16 

 mgm per cm- reduces the intensity of the ^-rays emitted by a hafniinn 

 oxide layer of 230 mgm/cm^ to one half of its initial value. The com- 

 parison of the absorbing power of aluminium for the /5-rays of hafnium 

 and scandium, decaying with periods of 55 and 90 days respectively, 

 shows no great difference ; the ratio of the two half- value thicknesses 

 l)eing 1.2. The softness of the hafnium radiation is partly responsible 

 for the low activities ol)tained after long exposure of hafnium oxide 

 with radium-beryllium sources of a few hundred millicurie, the /5- 

 ladiation emitted being absorbed to an appreciable extent in the haf- 

 nium oxide sample itself. In the case of hafnium, as already mentioned, 

 every place between the mass numbers 176 and 180 is occupied by a 

 known stable isotope ; the formation of the active hafnium isotope 

 is presumably due to the process 



vaHf-f on = 72Hf. 



On emitting /^-rays according to the equation 



'?^Hf = mi\ -f (^ 



the active hafnium isotope becomes the only stable isotope of tantalum 

 known. Hafnium is thus partly converted into tantalum under the 

 action of neutron bombardment, while, as shown by us previously, 

 hafnium is formed under the action of neutrons on lutecium. It is quite 

 possible that, under bombardment with a powerful stream of deuterium 

 or of neutrons, further decay periods of hafnium will be discovered. 



THE EFFECT OF NEUTRON BOMBARDMENT ON SCANDIUM 



A few years ago we embarked on the investigationof the effect of neut- 

 ron bombardment on scandium, (4), (5), (6), chiefly in the hope of being 

 able to prepare an artificial radioactive isotope of potassium and to ob- 



O llevesy 



