---
category: Scientific Theory & Technology
start: 1939
summary: Critical mass is the minimum amount of fissile material required for a self-sustaining
  nuclear chain reaction, first calculated for uranium by French physicist Francis
  Perrin in 1939 and central to both nuclear weapons design and proliferation intelligence.
tags:
- Concept
- Nuclear
- Physics
---

Critical mass refers to the smallest amount of fissile material needed for a sustained nuclear chain reaction. Francis Perrin, a French scientist, was the first to publish a formula for calculating the critical mass of uranium in 1939.[^1]

[^1]: Hersh, Seymour M. *The Samson Option: Israel's Nuclear Arsenal and American Foreign Policy*. Random House, 1991. Chapter 2.