History of plutonium - DOE-HDBK-1145-2001

Radiological Safety Training for Plutonium Facilities

DOEHDBK11452001

Student's Guide

I. History of plutonium

A. Discovery

In the earlier part of this century (1900-1940),

physicists speculated that there might be elements

with higher atomic numbers than uranium (at the time,

the element with the highest known atomic number).

The first of these elements was found in 1940 at

the University of California (Berkeley) by Edwin M.

McMillan and Philip H. Abelson. The element was

called neptunium after the planet Neptune. A few

months later, Arthur C. Wahl, Glenn T. Seaborg, and

Joseph W. Kennedy produced plutonium by

bombarding uranium-238 (U-238) with deuterons in an

accelerator called a cyclotron (also called an "atom

smasher"). The cyclotron is a large machine that uses

electromagnets to accelerate charged atomic particles

(protons and beta particles) to extremely high speeds

and then smash them into a target material.

B. Early research

On March 28, 1941, scientists at the University of

California (Berkeley) demonstrated that plutonium-239

(Pu-239) could undergo fission with thermal/slow

neutrons. Fission is the process of splitting atoms

through which large amounts of energy (200 Mev per

fission as compared to 4 ev released during

combustion of an atom of carbon) are released, as

well as excess neutrons (between two and three),

which can then split other atoms to keep a chain

reaction going.