Noddack was not the only critic of Fermi's claim. Aristid von Grosse suggested that what Fermi had found was an isotope of protactinium. Meitner was eager to investigate Fermi's results, but she recognised that a highly skilled chemist was required, and she wanted the best one she knew: Hahn, although they had not collaborated for many years. Later Meitner said about Hahn (and Friz Strassmann, who joined later); "It(nuclear fission) succeeded with an unusually good chemistry of Hahn and Straßmann, with a fantastically good chemistry that really no one else could do at that time. Later, the Americans learned it. But at that time, Hahn and Straßmann were really the only ones who could do it at all, because they were such good chemists. They have really proven a physical process with chemistry, so to speak." Initially, Hahn was not interested, but von Grosse's mention of protactinium changed his mind. "The only question", Hahn later wrote, "seemed to be whether Fermi had found isotopes of transuranian elements, or isotopes of the next-lower element, protactinium. At that time Lise Meitner and I decided to repeat Fermi's experiments in order to find out whether the 13-minute isotope was a protactinium isotope or not. It was a logical decision, having been the discoverers of protactinium."