Branching ratio to the 803 keV level in Po210α decay

Precise knowledge of the branching ratio in the alpha decay of Po-210 is important for accurate measurement of the Bi-209(n, gamma)Bi-210g cross section, the reaction involved in the termination of the astrophysical s process. The branching ratio was determined from independent measurements of alpha and gamma 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) x 10(-5), consistent with the results of several measurements performed six decades ago. As a by-product value the Bi-209(n, gamma)Bi-210g thermal cross section was measured to be 21.6 +/- 1.1 mb.