MEASUREMENT OF THE HALF-LIFE OF THE FIRST EXCITED-STATE OF PB-205

The inverse beta decay Tl-205(v, e)Pb-205 can be used to investigate t he solar neutrino flux averaged over the last several million years. T he inverse P decay proceeds dominantly via the 2.3 keV level of the Pb -205 and an accurate estimate of the cross section depends on our know ledge of the structure of the 2.3 keV level. We have made the first me asurement of the half-life for the decay of the 2.3 keV level to the P b-205 ground state. Our result is T-1/2 = 24.2 +/- 0.4 mu s and can be used to improve our knowledge of the structure of the two Pb-205 stat es.