The density of niton (“radium emanation”) and the disintegration theory

Abstract

According to the disintegration theory of radioactive change, a definite number of atoms of radium break up per second, each evolving an α -particle which ultimately becomes a helium atom, leaving behind lighter molecules which form the gas known as “radium emanation,” or niton. The identity of the α -particle after it has lost its electric charge with the helium atom has been convincingly proved by Rutherford and Geiger; and measurements of the volume of helium evolved from niton by Ramsay and Soddy, and from radium in equilibrium with its disintegration-products by Dewar, render it exceedingly probable that in each successive change from radium to radium D only one α -particle is expelled per atom. If, then, the view is held that the radium atom on disintegration to niton splits up into two parts only, one of which is the α -particle, then the atomic weight of the resulting niton is 226·4—4 = 222·4. On the other hand, it may be supposed that the disintegrating radium atom splits up into three or more parts; helium, and two other bodies of higher atomic weight, if three parts. On account of its greater mass, the heavier particle might be expelled below the critical velocity necessary for the formation of ions in the air, and might itself be non-radioactive; if this were the case, its presence in a solid state would almost certainly escape detection. There is no direct evidence against such a supposition, for the atomic weights of none of the products of the disintegration of radium have been determined. Experiment alone can settle this question of the true atomic weight of niton; but on account of the exceedingly small volume of this gas obtainable from a relatively large weight of radium, the experiment is by no means easy.