Enrico Fermi had begun this line of work, when he showed that neutrons work better than protons for penetrating and transforming a nucleus. By 1938, Hahn and Strassmann were among a number of scientists who were trying to find out what products are formed if you shoot neutrons into heavy elements. They hoped to find elements even heavier than uranium. Such altogether new elements would surely have scientific interest, and perhaps even practical uses. But the substances Hahn and Strassmann produced looked like radium or barium, two known and almost chemically identical elements...
HAHN: We made precipitations, Strassmann and myself, where we could be absolutely sure that there could be nothing else but either radium or barium.
But physicists did not suppose a heavy element like uranium could be transformed into a light element like barium. You might be able to knock off four protons from the nucleus of the uranium atom and create radium. But to get from uranium to barium, the neutron would have to chip off 100 particles! That seemed flatly impossible. Barium was out of the question...
HAHN: Therefore, we could conclude that the substances could be really only radium because barium was prohibited by the physicists that we didn't dare to think it barium in those times. We always tried to explain what is wrong in our experiments, not to say we do have barium, but we always thought it can't be there and therefore we have to say, "What is the nonsense we are doing?" So really, it is so, that we poor chemists—isn't it the same with you?—we are so afraid of these physics people.
Hahn wrote to Meitner in December of 1938 describing the "strange results" he and Strassmann had found. Meitner was equally baffled—at first. Later that month, shortly before Christmas, her nephew Otto Frisch visited her in Sweden. Frisch was a physicist who worked at Niels Bohr's famous Institute for Theoretical Physics in Denmark. Years later, Frisch recalled his visit to Meitner in December of 1938...
FRISCH: Lise Meitner was in Sweden and was lonely so I offered to come and visit
her, and we met in the west of Sweden in a small place near Goteborg, and
when I came she was brooding over a letter of Hahn. And then we sort of
kept rolling this thing around and saying, "Barium, I don't believe
it. There's some mistake. You couldn't chip
a hundred particles off a nucleus in one
blow. It's fantastic. It's quite impossible, a single neutron could do that."
And I still don't know how we got to the concept of fission, 
but
I remember Lise Meitner drawing a dotted circle on a piece of paper and
saying, "Couldn't it be this sort of thing?" Now she always rather
suffered from an inability to visualize things in three dimensions, whereas
I had that ability quite well. And I had, in fact, apparently come around
to the same idea, and I drew a shape like a circle squashed in at two opposite
points. And Lise Meitner then said, "Well, yes, that is what I mean.
" Apparently she had, so to say, looked at the nucleus from the poles
on, and with the dotted line was indicating the equator being pushed inwards.