Nuclear weapons and reactors get their chain reactions underway via neutron radiation, but do other radiation particles ever contribute?

  • $\begingroup$ It's important to keep in mind the distinction between fission and chain reaction fission, where the neutrons from one fission event go on to trigger further fissions. $\endgroup$ Sep 25, 2020 at 21:16

1 Answer 1


Gamma initiated fission is well known, being studied from the very beginning of nuclear physics (lots of work using photofission to understand energy levels in light nuclei) . A little-known feature of the Evaluated Nuclear Data Files is that it has evaluated cross sections for gammas as well as for neutrons. I use the mirror at Brookhaven.

As an example, I enter '238U' for the Target, 'g,*' for the Reaction (not noted in the suggested list to the left - sigh), and 'sig' for the Quantity, hit return, and get a listing of 5 different types of gamma cross sections. If I select the "U238(G,F),SIG" (yes, "F" for Fission, not Fluorine) entry and plot it I get:

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