How the current high-precision experiments challenge the usual beta decay and electron capture models

Atomic and nuclear decay data of high-precision are mandatory in the context of radionuclide metrology and are of importance in a wide range of communities. A novel experimental technique, metallic magnetic calorimetry, has recently been adapted to measure low-energy beta and electron capture emissions. The high precision measurement of 63Ni and 241Pu beta spectra highlights an important discrepancy compared with the usual theoretical predictions for these simple transitions. The same was found in the 138La decay measured with a LaBr3:Ce scintillator.
Starting from a usual beta decay model, a home-made code for calculating beta spectra has been developed to accurately account for the atomic screening and exchange effects, leading to excellent agreement with the measurements. A first simplified version of this code, BetaShape, has been released and includes a database of experimental shape factors. Recently, the calculation of electron capture decay has also been addressed. These recent achievements and ongoing work will be presented in detail.