Hitchins helped to determine the atomic weight of lead based on measurements of radioactive ores, work that was important in developing an understanding of isotopes. The samples of distilled lead which Hitchins prepared from Ceylon thorite were used by Frederick Soddy and supplied by him to Otto Hönigschmid, who did important  work confirming that the atomic weight of thorium lead is higher than that of common lead.
Soddy indicated that Hitchins also worked on the actual analyses, in his published report of 1917: "According to analyses by Miss A. F. R. Hitchins and myself, the 20 kilos of selected thorite worked upon contained 0-4 per cent, of lead, 57 per cent, of thorium, 1-03 per cent, of uranium, and 0-5 c.c. of helium per gram." This work proved that atomic weight was not a constant. Chemically pure elements could be mixtures of isotopes with differing atomic weights.