Between 1934 and 1938, Hahn, Meitner, and Strassmann found a great number of radioactive transmutation products, all of which they regarded as transuranic. At that time, the existence of actinides was not yet established, and uranium was wrongly believed to be a group 6 element similar to tungsten. It followed that the first transuranic elements would be similar to group 7 to 10 elements, rhenium and platinoids. They established the presence of multiple isotopes of at least four such elements, and (mistakenly) identified them as elements with atomic numbers 93 to 96. They were the first scientists to measure the 23-minute half life of the synthetic radioisotope uranium-239 and to establish chemically that it was an isotope of uranium, but with their weak neutron sources they were unable to continue this work to its logical conclusion and identify the real element 93. They identified ten different half lives, with varying degrees of certainty. To account for them, Meitner had to hypothesise a new class of reaction and the alpha decay of uranium, neither of which had ever been reported before, and for which physical evidence was lacking. Hahn and Strassmann refined their chemical procedures, while Meitner devised new experiments to examine the reaction processes.