Discussion on heavy hydrogen

In the history of Physical Science, it is a commonplace that a new discovery which at first appears to be of purely scientific interest, ultimately, within a period of twenty years or more, is found to have useful practical applications, This is well illustrated by the discovery of the rare gases in the atmosphere, neon, and argon, which are now used in quantity for industrial purposes. The fundamental discovery in 1919 of the isotopic constitution of the majority of our elements, so largely due to Aston, at first sight appeared to be of purely scientific significance, but we shall see from the discussion to-day that it may ultimately have wide practical consequences in many directions. It is hardly necessary to discuss in detail the history of the discovery and separation of heavy hydrogen, in which scientific men in the U. S. A. have taken such a leading part. The proof that oxygen was not a simple element but contained two isotopes in small quantity of masses 17 and 18, indicated that there was a small discrepancy of about 2 parts in 10,000 between the measurements of the relative masses of hydrogen and oxygen found by Aston and those found by direct physical and chemical methods. Birge and Mendel suggested that this discrepancy might be due to the presence of an isotope of mass 2 present in ordinary hydrogen. This gave the necessary impetus to Urey, Brickwedder and Murphy to tint whether the presence of H2 could be detected by direct optical methods. The experiments were successful in showing a small trace of H2 , estimated initially at about 1 in 4000 of the H1 isolope. The wave-length of the α line of H2 was found to be 1·79 A units greater than for H1 —a result agreeing closely with the theoretical value to be expected for an isotope of hydrogen of mass 2. The mass of the new isotope was directly measured by Bainbridge, using it modified type of mass spectrograph, and found to be 2·0136, slightly less than the weight of the ordinary hydrogen molecule 2·0156 in terms of O = 16.