/sup 148,150/Sm: A test for s-process nucleosynthesis

We have measured to a precision of approx.4.5% the neutron capture cross sections of /sup 148,149,150/Sm over the neutron energy range 4N/sub s/ (Maxwellian-averaged neutron cross section times s-process abundance) for the s-only isotopes /sup 148,150/Sm is 0.91 +- 0.03 rather than unity as predicted by the local approximation. We interpret this result as due to an s-process branching which partly bypasses 148Sm. Since the β-decay rates at the branching points are expected to be almost independent of temperature, we are able to obtain an estimate of the s-process neutron density of n/sub n/ = 1.0 +- 0.4 x 108 cm-3. The new results have also served to considerably improve the N/sub s/-systematics in the mass region Aroughly-equal145