7 - Little Boy and Fat Man: relativity in action

Summary

I do not believe that civilization will be wiped lout in a war fought with the atomic bomb. Perhaps two-thirds of the people of the earth might be killed. But enough men capable of thinking, and enough books, would be left to start again, and civilization could be restored.

Albert Einstein, in Atlantic Monthly, 1945

Prologue

In this chapter, we explore me application of special relativity to nuclear physics. As in chapter 6, the reader need only read the following overview to gain an impression of the impact Einstein's theory has had on our understanding of nuclear structure and nuclear reactions. The story of Einstein's development of the theory of general relativity is taken up in chapter 8: the rest of this chapter is not essential for an understanding of the remainder of this book.

The story begins with Ernest Rutherford and Frederick Soddy quantifying the amount of energy released in radioactive decays and their joint realization that such a huge energy source could be a mixed blessing for humanity. Francis Aston, working in Cambridge with Rutherford, invented the ‘mass spectrograph’ and was able to separate different ‘isotopes’ of many elements. There was much confusion about the nature of ‘isotopes’ until James Chadwick discovered the neutron in 1932. Aston had also realized that the neutrons and protons when bound in the nucleus weigh less than in their free state. The difference arises from the nuclear binding energy, which results from the strong nuclear forces holding the nucleus together. This is a direct example of Einstein's mass-energy relation.