Determination of the shape factor of 90Sr by means of the cutoff energy yield method

Usually, Kurie plots are used to analyze beta-spectra shape-factor functions measured by means of semiconductor and magnetic spectrometers. A drawback of these techniques is the occurrence of self-absorption within the samples through which the emission spectrum is altered. In liquid-scintillation samples self-absorption does not occur, but the poor energy resolution makes the analysis of the spectra difficult. To overcome this problem, two resolution-invariant observables are used for determining the shape-factor function of 90Sr: (1) the maximum point energy and (2) the cutoff energy yield. The measured shape-factor function of 90Sr agrees with the one which is predicted by theory for the first-forbidden unique transition.