Determination of the shape factor of (90)Sr 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 (90)Sr: (1) the maximum point energy and (2) the cutoff energy yield. The measured shape-factor function of (90)Sr agrees with the one which is predicted by theory for the first-forbidden unique transition.

Activity standardization by liquid scintillation counting and half-life measurements of

Radioactive 90Y was standardized by means of 4piBeta liquid scintillation efficiency tracing with a two-phototube counting system. The efficiencies of 90Y and the tracer 3H are related by the CIEMAT/NIST method. The dependence of the calculated efficiency on various shape factors and the importance of accurately measuring the radionuclide impurity of 90Sr are discussed. The half-life of 90Y was measured with improved accuracy by means of a liquid scintillation counting and a 4pi ionization chamber measuring system, and an average value T1/2 = 64.053(20) h was found.