NUCLEUS OF THE ATOM ANDERSON 243 



THE DEUTON 



Spectroscopy, the study of light emitted by atoms under various 

 conditions, has during the past several years played a major role in 

 unraveling the mysteries concerning the behavior of the extranu- 

 clear electrons. In 1931 it was responsible for a discovery of the 

 first magnitude in the realm of nuclear physics. The wave length 

 of the light emitted by an atom depends upon the energy change in- 

 volved when an extranuclear electron transfers its position from one 

 orbit to another. The amount of this energy change is determined, 

 of course, chiefly by the charge upon the nucleus about which the 

 electron revolves. The electron does not in fact revolve about the 

 nucleus as a center; but both nucleus and electron revolve about 

 their common center of gravity. Hence the size of orbit, and there- 

 fore the wave length of the light emitted, depend in some measure 

 upon the mass of the nucleus, as well as upon its charge. H. C. 

 Urey, G. M. Murphy, and F. G. Brickwedde, early in 1932, in photo- 

 graphing the spectrum of hydrogen, observed in addition to a well- 

 known bright red line of hydrogen a faint line slightly displaced. 

 These men correctly interpreted the new line as showing the exist- 

 ence of a new kind of hydrogen atom, a new isotope of hydrogen, to 

 the nucleus of which the name " deuton " has been given. All hydro- 

 gen nuclei had previously been considered to consist simply of a 

 single proton. Here, as measurements on the displaced line showed, 

 was evidence of a new hydrogen nucleus having approximately twice 

 the mass of a proton, and constituted presumably of a proton and 

 neutron in close combination. The chemical properties of an atom 

 depend upon the number of extranuclear electrons and therefore 

 upon the nuclear charge and not upon its mass. The new hy- 

 drogen, to which the name " deuterium " was given, forms water by 

 combination with oxygen in a manner exactly identical with the 

 well-known oxidation process of ordinary hydrogen into water. 

 The new water, or " heavy water ", chemically is pure water ; but 

 its physical properties, such as density, boiling and freezing points, 

 differ slightly from ordinary water. 



Heavy water can be conveniently prepared simply by passing an 

 electric current through ordinary water until only a small residue 

 of the water is left. Ordinary water contains normally about 1 part 

 in 6,000 of heavy water. By continued electrolysis this concentra- 

 tion can be increased to any desired extent. Heavy water, 99 percent 

 pure, was first prepared by G. N. Lewis, and is now sold in the 

 market as a commercial product. To the nuclear physicist, deutons, 

 obtained from heavy water, have become exceedingly valuable as 

 projectiles in the bombardment experiments to be described. Here, 



36923—36 17 



