Comments on the Frisch-Peierls Estimate of the Critical Mass of a Uranium Fission Bomb

Abstract

The Frisch-Peierls memorandum of March 1940 opened the way to nuclear weapons through its conclusion that the critical mass for an explosive chain reaction in ²³⁵U could be as small as 0.6 kg. This gross underestimate was based on the conjecture that the cross section for the fission of ²³⁵U with fast neutrons was 10 barns. Though this value turned out to be far too high, it is argued here that the choice made was not unreasonable at the time.

Keywords:

• Fission cross section, geometrical limit, de Broglie wavelength

Acknowledgments

I am indebted to B. Cameron Reed for a critical reading of the manuscript and his many helpful comments. In particular, I thank him for drawing my attention to Ref. [4].

Disclosure Statement

No potential conflict of interest was reported by the author.