In physics textbooks with chapters about nuclear fission there is often a historical introduction about Otto Hahn. That he tried to generate transuranium but discovered the nuclear fission.
If you start with uran (atomic number 92) you need to increase the atomic number i.e. the number of protons in the nucleus. However if you just add (naively) a neutron you just and up with another isotope (but not with another element i.e. not transuranium).
So which facts were known in 1938 to Otto Hahn which lead him to try neutrons to generate transuranium? What was his reason to try it with neutrons?