Decay ofTl210to States ofPb210

The decay of ${\mathrm{Tl}}^{210}$ sources was investigated by means of scintillation and semiconductor spectrometers. $\beta -\gamma$, $\gamma -\gamma$, and $\gamma$-sum-coincidence measurements were carried out. The $\beta$ spectrum (from shell-model considerations presumably a first-forbidden transition) was decomposed into three components of 2.34±0.10, 1.87±0.10, and 1.32±0.10 MeV. Twenty-four $\gamma$ lines were found decomposing the Nal(Tl) scintillation spectrum; six of them showed measurable conversion lines in the semiconductor spectrometer and their transition type could be inferred. Measurements of the delay of different parts of the $\gamma$ spectrum with respect to the $\beta$ rays revealed the existence of at least three states of measurable half-life, 1.7±0.1, 1.1±0.1, and 0.6±0.1 nsec, the latter arising from the second excited state of 1.09 MeV. Calculations of the ${\mathrm{Pb}}^{210}$ levels were carried out, using a zero-range approximation for the interaction between the two extra neutrons and compared with the experimental level scheme.