| MadSci Network: Physics |
Guenther, Since you indicate you are a grad of a science program, I will address my answer at that level. For alpha and gamma decay, the half-life is a constant. For beta decay, which includes beta-minus (electron) decay, positron decay, and electron capture, it is possible to effect changes in the half life of radionuclides decaying by electron capture. Electron capture involves the capture of an orbital electron by a proton in the nucleus changing it into a neutron. This has the same effect as beta minus (electron) decay; decreasing the atomic number by 1 and leaving the mass number unchanged. Capture of a K-shell (principal quantum number = 1) electron in the most common form of electron capture decay. The wave function description of an electron will show an overlap with the nucleus (the electron is "in" the nucleus) part of the time. It is this part of the time that can be changed by chemical means, and that changes the half life for electron capture decay. The largest change in half life that has been observed is a 3.6% increase in the half life between Nb-90m metal and Nb-90mF5 complex. The fluoride complex "pulls" the electron density cloud away from the nucleus toward the fluorines decreasing the density around the nucleus, and the time the electron spends in the nucleus. One textbook with a couple of pages on Electron Capture decay is "Radiochemistry and Nuclear Methods of Analysis" William D. Ehmann and Diane E. Vance Wiley Interscience Publication John Wiley & Sons, Inc. New York 1991 ISBN 0-471-30628-2 (pbk) You can also input electron capture decay half life changes into the Google search engine. Several of the hits further discuss electron capture decay. This is really a laboratory curiosity, rather than a physically important effect in nature.
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