When Hitchins first worked with Soddy, researchers were still searching for new chemical elements, and isotopes were not yet understood.  As early as 1904, researchers had hypothesized that the decay of uranium resulted in the creation of radium, but how this occurred was not clear.  In 1907, the American radiochemist Bertram Boltwood had isolated what he believed to be a new intermediate element in the decay chain between uranium and radium, "ionium". Researchers eventually determined that ionium was actually an isotope of thorium, Th.
Soddy asked Hitchins to investigate ionium.  She selectively extracted uranium from ore samples to create purified uranium preparations and established a half-life for ionium. Her research also showed that there was a steady rate of increase in the amount of radium in her uranium solutions, the first direct experimental evidence that radium was formed by the decay of uranium. Her results were published in 1915.