Moxon-Rae setup for the measurement of stellar (n,γ) rates and the example of 87Rb

A setup with Moxon-Rae detectors was optimized for measurements of (n,γ) cross sections in the keV region. The experimental technique makes use of the quasi-Maxwellian spectrum that can be obtained via the 7Li(p,n)7Be reaction and is particularly suited for the determination of Maxwellian-averaged cross sections for nucleosynthesis studies related to s-process scenarios. It allows measurements at extremely short flight paths with the time-of-flight method as an option for background reduction. The experimental determination of the efficiency with calibrated γ sources and with two-step cascades from selected resonances of the 34S(p,γ) reaction revealed new properties of the response function. The reliability of the method was first demonstrated at the example of the well-known ratio of the (n,γ) cross sections of Ta and Au, and then used for a measurement of the stellar 87Rb cross section. With this new value left-angle σv right-angle/vT=15.5±1.5 mb, a discrepancy in the previously existing data could be resolved. copyright 1996 The American Physical Society