Study on radionuclide half-life length: safeguarding the unit becquerel
The exponential decay of radionuclides as a function of time is a cornerstone of nuclear physics. Decay constants for spontaneous radioactive decay are considered invariable in time and space. This convenient trait allows projecting activity values to a point of time in the past or the future. The exponential-decay law has many applications, e.g. in nuclear dating for archaeology, geo- and cosmochronology, dosimetry in nuclear medicine, nuclear waste management, etc.
In recent years there have been several claims from scientists saying that they have found proof that the half-lives of radionuclides are not constant, but depend on external influences like the Earth-to-Sun distance. Such claims, if true, would have a fundamental impact on our society. We would not be able to trust archaeological dating based on e.g. C-14 or the age of Earth derived from the U-238 decay chain. We would not be able to perform accurate planning for cancer treatments or to predict the radiation dose from nuclear waste, just to mention a few examples. In fact, the foundation of all radioactivity measurements would have to be redesigned.
Stefaan Pommé of JRC-Geel has taken the initiative to conduct the biggest study ever to clarify the situation. He collected the very best long-term activity measurements of different radionuclides measured in specialised national metrology institutes across the globe, covering 4 continents and spanning a period of six decades. By performing statistical tests and analyses on all data sets, it was proved that radioactive half-lives are not influenced by the proximity to the Sun. This work was supported by the Consultative Committee for Ionising Radiation, which takes responsibility for the SI unit becquerel (Bq) for radioactive decay. The study confirms that the foundation of our common measurement system of radioactivity is valid and that radioactivity behaves the same in every place on Earth.