Yields of two-nucleon-out residual products from stopped π^{-} reactions

Yields of two-nucleon-out products from stopped ..pi../sup -/ reactions in /sup 26/Mg, /sup 74/Ge, /sup 97/Mo, /sup 114/Cd, /sup 142/Ce, and /sup 174/Yb have been measured by activation techniques. These products result predominantly from pion absorption at the nuclear surface when the absorbing pair of nucleons escapes the nucleus leaving behind very little excitation energy (< or approx. =8 MeV). The ratios of the yields of the nn-out to the np-out products following stopped ..pi../sup -/ absorption increase monotonically from 6.8 for /sup 26/Mg to 18.2 for /sup 174/Yb. The data have been fitted using a pion absorption model that uses separate density distributions for neutrons and protons, and a three to five percent greater root-mean-square radius for neutrons is indicated.