"Following the discovery of radioactivity by Becquerel in 1896, an intense effort was mounted to ascertain whether the decay rates of nuclides could be affected by external influences including temperature, pressure, chemical composition, concentration, and magnetic fields. By 1930, Rutherford, Chadwick, and Ellis concluded that “The rate of transformation of an element has been found to be a constant under all conditions.” (For decays resulting from K-capture, or for beta-decays in strong ambient electromagnetic fields, the situation is slightly more complicated, since these decays are influenced by the electron wave functions which can be affected by external pressure or fields.) For ³²Si and ²²⁶Ra, which decay by beta- and alpha-emission, respectively, fluctuations in the counting rates (in the absence of strong external electromagnetic fields) should thus be uncorrelated with any external time-dependent signal, as well as with each other. In what follows we show that neither of these expectations is realized in data we have analyzed for ³²Si and ²²⁶Ra, thus suggesting that these decays are in fact being modulated by an external influence."

-- Jere H. Jenkins, Ephraim Fischbach, John B. Buncher, John T. Gruenwald, Dennis E. Krause, and Joshua J. Mattes, Evidence for Correlations Between Nuclear Decay Rates and Earth-Sun Distance.