62 ADVENTURES IX RADIOISOTOPE RESEARCH 



leads chiefly to the formation of higher stable isotopes. It is therefore 

 even elements that undergo an increase of their equivalent weights 

 with time while the relative abundance of the elements of odd atomic 

 number shifts towards the heavier elements. 



Below zinc, conditions are very different : the result of neutron action 

 in minerals leads here often to the formation of elements of lower 

 atomic number and only to a smaller extent to the formation of 

 heavier isotopes or heavier elements. For example, bombardment 

 of aluminium leads to the formation of a magnesium isotope and to 

 a sodium isotope ; the branching ratio between these two processes 

 depends greatly on the energy of the neutrons. 



Sunimary 



The artificial ladioactivity of the rare earth elements including scandium 

 and yttrium was investigated. The periods of decay of numerous radioactive 

 isotopes produced lie between 5 min. and a few month . The biggest and smallest 

 saturation intensities of the radiation emitted by these isotopes are in the ratio 

 10,000 : 1. The half- value thickness in aluminium of the (^-radiation emitted 

 was measured in several cases, and, in some cases, the maximum energy of the 

 continuous ^-ray spectrum and Fermi's constant a as well. 



The absorption of slow neutrons in rare earth elements was measured with 

 a view to disco\ering the presence of strongly absorbing nuclei not giving rise 

 to active isotopes. 



The application of artificial radioactivity to analytical chemistry is discussed. 



It is shown that the combination weight of the rare earth elements occurring 

 in minerals in which a continual production of neutrons takes place has undergone 

 a slight change during geological time. 



References 



1. E. AMAI.DI, E. Fermi et al., Proc Roy. Soc A. 149, 522 (1935). 



2. G. Hevesy and Hilde Levi, Nature 136, 103 (1935) and Nature 137, 849 

 (1935). G. Hevesy, Nature 135, 96 (1935); Roy. Danish Acad. (Math.-fys. 

 Medd.) XIII, 3, (1935). 



3. S. SuGDEN, Nature 135, 469 (1935). 



4. J. K. Marsh and S. Sugden, Nature 136, 102 (1935). 



5. I. C. McLennan and W. H. Rann, Nature 136, 831 (1935). 



6. E. Bona, Wiener Akad. Anzeiger 27, (1935) and 73, 159, (1936). 



7. J. C. Chadwick and M. Goldhaber, Camb. Phil. Soc. 31, 612, (1935). 



8. J. R. Dunning, G. B. Pegram, G. A. Fink and D. P. Mitchell, Phtjs. 

 Rev. 48, 265, (1935). 



9. N. Bohr, Nature 137, 344 (1936). 



10. H. A. Bethe, Phys. Rev. 50, 332 (193G). 



