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A physicist who helped explain nuclear fission. Lise Meitner and Otto Robert Frisch interpreted the energy release associated with the chemical findings of Otto Hahn and Fritz Strassmann. Following these contributions together distinguishes the identification of reaction products from their physical explanation.^[ref]

Nuclear fission splits an atomic nucleus into two major fragments, usually accompanied by emitted neutrons and gamma rays. It can follow neutron absorption or occur spontaneously in some heavy nuclides. When the products have greater total nuclear binding energy, the decrease in rest energy supplies fragment kinetic energy and radiation.

The fragments are often neutron-rich and undergo subsequent beta decay, producing an evolving inventory of fission products. Some emitted neutrons can cause further nuclear fission, enabling a nuclear chain reaction; others are absorbed without fission or escape.

The discovery combined chemical and physical evidence. Otto Hahn and Fritz Strassmann identified barium among products of neutron-irradiated uranium, rather than merely an adjacent heavy element. Lise Meitner and Otto Robert Frisch interpreted this as division of the atomic nucleus and estimated the large released energy from mass differences. Chemical separation identified the unexpected product: the same procedure could separate a radium isotope from barium, whereas the new radioactive activity followed barium. This chemical comparison did not by itself measure every fragment's motion.^[ref]

Otto Robert Frisch and Lise Meitner interpreted the barium found after uranium bombardment as evidence that a heavy atomic nucleus could divide into two large fragments. Their 1939 paper related the available energy to nuclear mass differences and the electrical repulsion of the fragments. This supplied a physical account of nuclear fission, connecting a chemical identification of the products with a new type of nuclear transformation and its large energy release.^[ref]

A physicist who worked with Lise Meitner on the interpretation of nuclear fission.^[ref]