Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 34 - Think and Explain - Page 654-655: 65



Work Step by Step

As stated in the footnote on page 640, U-235 decays faster than U-238 (an Internet search shows that its half-life is about 704 million years compared to U-238's half-life of 4.5 billion years). If Earth were older, uranium deposits would contain an even smaller percentage of U-235 than they do now. Fermi would still have needed to enrich his uranium fuel to make it go critical.
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