New methods for the determination of β-spectra shapefactor coefficients

The maximum point of a logarithmic β-decay distribution is a quite well-defined point, which can be used for the calibration of liquid scintillation logarithmic spectrometers. It is observed that maximum points of several β-ray nuclides with forbidden transitions, such as 204Tl, 36Cl, 137Cs, 89Sr and 90Y, lie outside of this calibration curve, indicating the presence of inaccuracies in the current shapefactors of these nuclides. For β-ray nuclides below the Cherenkov threshold in the scintillation mixture, such as 129I, the CIEMAT/NIST method can be used for the accurate determination of the shapefactor coefficients.