Scientists have detected perturbations of the radioactive decay constant related to solar activity.
In 1930, the “father” of nuclear physics Ernest Rutherford, together with James Chadwick and Charles Ellis, concluded in their definitive Radiations from Radioactive Substances that the rate of transformation is a constant under all conditions.
A team of researchers at Brookhaven National Laboratory observed the decay constant of silicon-32 from 1982 to 1986 and found that the decay constant varied around its usual value of about 172 years by almost 0.1%. The modulation appeared to be in phase with the varying distance of the Earth to the Sun: in January, when the Earth is closest, the decay rate was faster; in July, when the Earth is farthest, it was slower
Purdue physicists, Ephraim Fischbach and Jere Jenkins, observed dips in the decay rate of manganese-54 associated with solar flare events in December, 2006.
According to our current understanding of physics, these variations should not occur. Some wild explanations involving neutrinos and perturbations in the fabric of space-time have been postulated, but no convincing theoretical explanation has yet been found.