Chain reactions

Chain reactions and feedback

What happens when ${}^{235}U$ absorbs a neutron?

$${}^1{\rm n}+ {}^{235}{\rm U} \rightarrow {\rm fission}\ {\rm fragments} + ~2\,{}^1_0{\rm n}$$

$${}^1{\rm n} +{}^{239}{\rm Pu} \rightarrow {\rm fission}\ {\rm fragments} + 3\,{}^1_0{\rm n}$$

Born jewish in Budapest, Leo Szilard fled to London in 1933, where he patented (1936) the idea of a chain reaction. (Not in Uranium).

1938 - Szilard verifies neutron multiplication in Uranium.

The amount of energy released in each generation of splitting nuclei is a multiple of the generation before $=>$ exponential growth.

This is an example of positive feedback

Hahn bombarded Uranium with neutrons in 1938. Why didn't he die in the ensuing chain reaction?

${}^{235}_{92}$U splits and gives off ~2 neutrons,

But most naturally occurring Uranium is ${}^{238}$U which absorbs neutrons and eventually changes into Pu.

Neutrons might also escape before running into another uranium-238.