Halbwertszeit, Elektroneneinfangverhältnis und β-Spektrum des Tl204
Half-life,PL/PK-capture ratio andβ-spectrum of Tl204 were studied with a scintillation spectrometer. To avoid source absorption and scattering troubles, the Tl204 source was built in in the lattice of NaJ(Tl)-crystals. The half-life measurements were performed over a period of 2,2 years, and we obtained a half-life of 3.81±0.04 years. ThePL/PK-capture ratio was determined at 0.41±0.03. This ratio gives a desintegration energy of 442−24+30 keV for the unique first forbidden electron capture decay of Tl204. For the branching ratio of electron capture toβ−-decay we found a value of (2.15±0.06)% and for the ratio ofK-capture toβ−-decay a value of (1.53±0.05)%. Theβ−-spectrum of Tl204 was measured from 200 down to 6 keV and yields an experimental shape factor which deviates below an energy of ∼90 keV from the theoretical shape factorq2L0+9L1. Reasons for this deviation which is opposite to the one obtained with magnetic spectrometers are discussed.