Tube Alloys - Uranium Enrichment

Uranium Enrichment

The British put much effort into exploring the possibility of successfully enriching the minimum required quantity of uranium. Dr. Rudolf Peierls, a German scientist who was working in the United Kingdom when Adolf Hitler came to power in Germany, and had then elected to stay, was working at the University of Birmingham. Peierls attempted to derive the critical mass of a block of pure uranium. In a paper entitled "Critical Conditions on Neutron Multiplication" delivered to the Cambridge Philosophical Society on 14 June 1939, he calculated that it was of the order of tons, too large to make into a practical bomb. However, with his friend Otto Frisch, a fellow German scientist living in exile in England, Peierls then began to examine the neutron cross-section of uranium-235, the rare lighter isotope that makes up only 0.7% of natural uranium, the rest being uranium-238. Their calculations indicated that it was within an order of magnitude of 10 kilograms (22 lb), small enough to be carried by a bomber of the day.