If the radioactive isotopes included radium, that was conceivable. Radium had an atomic number of 88, only four less than uranium’s 92. You could imagine that a neutron being absorbed by a uranium nucleus might make the latter so unstable as to cause it to emit 2 alpha particles and become radium. Barium, however, had an atomic number of 56, only a little over half that of uranium. How could a uranium nucleus be made to turn into a barium nucleus unless it more or less broke in half? Nothing like that had ever been observed before and Hahn hesitated to suggest it. While he was nerving himself to do so, however, Lise Meitner, in Stockholm, receiving reports of what was being done in Hahn’s laboratory and thinking about it, decided that unheard-of or not, there was only one explanation. The uranium nucleus _was_ breaking in half. Actually, when one stopped to think of it (after getting over the initial shock) it wasn’t so unbelievable at that. The nuclear force is so short-range, it barely reaches from end to end of a large nucleus like that of uranium. Left to itself, it holds together most of the time, but with the added energy of an entering neutron, we might imagine shock waves going through it and turning the nucleus into something like a quivering drop of liquid. Sometimes the uranium nucleus recovers, keeps the neutron, and then goes on to beta-particle emission. And sometimes the nucleus stretches to the point where the nuclear force doesn’t quite hold it together. It becomes a dumbbell shape and then the electromagnetic repulsion of the two halves (both positively charged) breaks it apart altogether. It doesn’t break into equal halves. Nor does it always break at exactly the same place, so that there were a number of different fragments possible (which was why there was so much confusion). Still, one of the more common ways in which it might break would be into barium and krypton. (Their respective atomic numbers, 56 and 36, would add up to 92.) Meitner and her nephew, Otto Robert Frisch (1904- ), who was in Copenhagen, Denmark, prepared a paper suggesting that this was what was happening. It was published in January 1939. Frisch passed it on to the Danish physicist Niels Bohr (1885-1962) with whom he was working. The American biologist William Archibald Arnold (1904- ), who was also working in Copenhagen at the time, suggested that the splitting of the uranium nucleus into halves be called “fission”, the term used for the division-in-two of living cells. The name stuck. In January 1939, just about the time Meitner and Frisch’s paper was published, Bohr had arrived in the United States to attend a conference of physicists. He carried the news of fission with him. The other physicists attending the conference heard the news and in a high state of excitement at once set about studying the problem. Within a matter of weeks, the fact of uranium fission was confirmed over and over.