Experiments and theory of 138La radioactive decay

International audienceWe measured with unprecedented accuracy key features of the La-138 radioactive decays as beta particle energy distribution from 0.5 keV to the end-point and ratios of electron capture probabilities P-L/P-K, P-M/P-K and P-M/P-L. This was achieved by making use of LaBr3:Ce and CeBr3 scintillator detectors. The advantage of the presented technique relies on the double role of LaBr3:Ce as source of La-138 and detector medium resulting in a relatively efficient counting statistics and unaltered beta energy detection. The experimental results are compared to advanced computational techniques and significant deviation is found below 20 keV with the computational spectrum showing a 5% excess of beta particle relative to the experimental spectrum at 10 keV