during the christmas holiday in 1938, frisch visited his aunt lise meitner in kungälv in sweden, where she had been forced to relocate after germany's annexation of austria made her a german citizen. while there she received the news that her former colleagues otto hahn and fritz strassmann in berlin had discovered that the collision of a neutron with a uranium nucleus produced barium as one of its byproducts. frisch and meitner hypothesized that the uranium nucleus had split in two. they estimated the energy released at around 200 mev, and frisch appropriated the term fission from biology to describe it. hahn's paper described the experiment and the finding of the barium byproduct. meitner's and frisch's paper explained the physics behind the phenomenon. frisch went back to copenhagen, where he was able to isolate the fragments produced by fission reactions. frisch later recalled that: