Radiopotassium and other Artificial Radio-elements

Abstract

IN a letter published in NATURE of January 19, it was shown that the bombardment of scandium with neutrons leads, beside the formation of an active scandium isotope1 20Sc46, to the formation of a new potassium isotope 19K42 having a half-life value of about 16 hours and emitting (-rays the intensity of which is reduced to one half of its initial value by an aluminium foil of approximately 0.7 mm. thickness. We were recently successful in preparing this potassium isotope K42 by the bombardment of calcium by neutrons according to the equation: Calcium carbonate, after being exposed to neutrons produced by a mixture of 200–300 mgm. radium emanation and beryllium powder, was dissolved in dilute hydrochloric acid, 150 mgm. sodium chloride added and the calcium precipitated as oxalate. The filtrate was found to be active and the measurement of both the rate of decay and the absorption of the radiation emitted has shown the presence of 19K42. The yield of K42 from calcium is a low one, which is due chiefly to the fact that the isotope Ca42 is only present to the extent of 0.8 per cent in the mixed element calcium. It is now possible to produce the potassium isotope K42 by each of the following reactions: When applying neutrons slowed down by Fermi's device by reflection by hydrogen nuclei, an active calcium isotope was obtained which decays with a period of 4 hours, the formation of which is due to one of the following two reactions: the latter being the more probable one.