Nuclear Clocks The Understanding the Atom Series Nuclear Energy is playing a vital role in the life of every man, woman, and child in the United States today. In the years ahead it will affect increasingly all the peoples of the earth. It is essential that all Americans gain an understanding of this vital force if they are to discharge thoughtfully their responsibilities as citizens and if they are to realize fully the myriad benefits that nuclear energy offers them. The United States Atomic Energy Commission provides this booklet to help you achieve such understanding. [Illustration: Signature of Edward J. Brunenkant] Edward J. Brunenkant, Director Division of Technical Information UNITED STATES ATOMIC ENERGY COMMISSION Dr. Glenn T. Seaborg, Chairman James T. Ramey Wilfrid E. Johnson Francesco Costagliola [Illustration: NUCLEAR CLOCKS] by Henry Faul CONTENTS INTRODUCTION 1 THEORY OF NUCLEAR AGE DETERMINATION 5 THE CARBON-14 CLOCK 9 Carbon-14 Counting 12 Carbon-14 Results 15 THE LONG-LIVED CLOCKS 19 The Rubidium-Strontium Clock 20 The Uranium Fission Clock 24 Plumbology 27 THE AGE OF THE EARTH 27 Analytical Techniques 31 Minerals That Can Be Dated 34 SOME INTERESTING RESULTS 40 The Old Man From Olduvai 40 The Geologic Time Scale 41 Precambrian Stratigraphy 47 AND WHERE DO WE GO FROM HERE? 48 GLOSSARY 49 APPENDIX 52 SUGGESTED REFERENCES 58 United States Atomic Energy Commission Division of Technical Information Library of Congress Catalog Card Number: 67-60195 1966; 1968(Rev.)