Maybe radioactivity hasn't revealed all its mysteries.
Radioactivity has a long history of confounding conventional scientific wisdom.
By the end of the 19th century, most physicists were convinced by the calculations of Lord Kelvin that the Earth was relatively young--perhaps much less than 100 million years old. But those calculations assumed that a primordial molten Earth had cooled to its current state without any new source of internal heat. After the discovery of radioactive elements in 1896, it soon became clear that the Earth possessed an inner warmth fueled by the elements' energy-releasing decay. So Kelvin's calculations had neglected an important effect, and the age of the Earth turned out to exceed 4 billion years.
Not long after, physicists began to notice a peculiar property of one particular form of radioactivity, beta decay. In beta decay an unstable nucleus emits an electron (labeled a beta particle before anybody knew what it really was). Beta decay was curious enough to begin with, since electrons don't exist within nuclei (and so apparently were created from neutrons). But even worse, the emerging electron flew off at any of a vast variety of speeds--implying that it could possess a wide range of energies. That defied standard physics, because the amount of energy possessed by the nucleus and its ejecta did not appear to be conserved.
For years this observation haunted physicists who revered the law of conservation of energy. Some, including the great Niels Bohr, proposed that the hallowed law might in some ways be violated. But then Wolfgang Pauli proposed that a ghostly new particle, later christened the neutrino, was also emitted in beta decay, carrying precisely enough energy to balance the books and save the energy conservation law.
Now Pauli's neutrino has turned up in another radioactive controversy. Some data analyses seem to suggest that the rate of radioactive decay for certain nuclei is not always the same. In fact, these studies find hints that decay rate depends on time of year, implying that perhaps the Earth's distance from the sun somehow exerts an influence, as Davide Castelvecchi describes in this issue (Page 20). Because the sun emits neutrinos, maybe some neutrino-induced action is messing with the supposed laws governing radioactive decay rates, some scientists speculate.
To be sure, there's no reason yet to throw out the nuclear physics textbooks. More often than not, anomalies of this nature reflect experimental errors or unforeseen factors that could explain away the discrepancies without resorting to breaking or changing any physical laws. But you never know.
Radioactivity has a way of revealing some of nature's best-kept secrets.--Tom Siegfried, Editor in Chief
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|Title Annotation:||FROM THE EDITOR|
|Date:||Nov 22, 2008|
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