External parameters can effect slight changes in the nuclear decay rate. B. Dudley's hypothesis. 11 Dudley rejects the idea that radioactive decay is completely spontaneous and instead hypothesizes that neutrinos from the neutrino sea, which has been suggested by others, trigger radioactive decay. Radiohalos are minute concentric rings of discoloration in minerals such as mica formed by alpha ray bombardment from radioactive inclusions. Radiohalos give evidence that decay rates vary with time.
Some researchers believe otherwise.
The speed of light may have been faster in the past . Morton has proposed that the permittivity of free space has changed. It then follows that the speed of light has changed. Furthermore, in the case of beta emission, Morton derives a relation between the nuclear decay parameter and the permittivity. If the permittivity has changed, it follows that the nuclear decay parameter has changed.