Zerfallsschema und β-Spektrum des MsTh1 (Ra228)

The β-spectrum of MsTh1 (Ra²²⁸) has been measured in a proportional counter in 2 π — and in 4π-geometry. Comparison of these measurements shows that there are no conversion electrons. The β-decay of MsTh 1 therefore leads in all cases to the ground level of MsTh2. The Kurie plot is straight from 15 keV up to the upper energy limit of E ₀=55±3 keV (log ft=5·6). The result has been checked by a search for photons emitted by the MsTh1. No γ-rays and no X-rays have been found. The measurements had to be made with a relatively large amount of natural Ra²²⁶ in the sources. — The results do not agree with those of Lecoin, Perey, Teillac and Riou, who proposed a complex decay sheme for MsTh1.