Science in 100 Key Breakthroughs by Paul Parsons

Author:Paul Parsons [Parsons, Paul]
Language: eng
Format: epub, pdf
Publisher: Quercus
Published: 2013-04-07T04:00:00+00:00

Parents and daughter nuclei

Rutherford’s idea also turned out to be flawed because helium can, in fact, escape from rock over time. But it was enough to inspire a young Bertram Boltwood at Yale University to carry out his own research. Rather than using helium levels, he looked at the amount of “parent” and “daughter” atomic nuclei in the rock. Rutherford had shown that when an atomic nucleus (the parent) decays, the particles it gives off alter its structure enough to change it into a new element (the daughter). For example, radioactive carbon decays by converting a neutron in its nucleus into a proton plus an electron. The electron is emitted as radiation while the proton remains, turning the carbon nucleus into nitrogen.

It was also known that the radioactivity of a given chemical element decays with a characteristic half-life—after which the number of parent nuclei will have decayed to half its original value. After another half-life period has elapsed, the parent number will have fallen to a quarter of its original value. And so on. Boltwood saw that by measuring the number of parent and daughter nuclei, he could work out the amount of radioactive decay and—using the known half-life of the parent—calculate how much time had elapsed since the decay had begun.

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