Branching ratio to the 803 keV level in Po 210 α decay

Precise knowledge of the branching ratio in the α decay of Po210 is important for accurate measurement of the Bi209(n,γ)Bi210g cross section, the reaction involved in the termination of the astrophysical s process. The branching ratio was determined from independent measurements of α and γ spectra of bismuth samples simultaneously irradiated by neutrons near the core of the Soreq research reactor (IRR1). The branching ratio was found to be (1.15±0.09)×10-5, consistent with the results of several measurements performed six decades ago. As a by-product value the Bi209(n,γ)Bi210g thermal cross section was measured to be 21.6±1.1 mb.