A detection system for (n,n′) reaction studies of astrophysical interest

We have constructed a new system to measure the (n,n) and/or (n,n′) reaction cross sections of a nucleus in the neutron energy range from a few to 100 keV using four 6Li-glass scintillation detectors for nuclear astrophysics interest. The detectors were enveloped in borated-polyethylene blocks to attenuate any neutron background caused by the scattering of neutrons from the 7Li(p,n)7Be reaction by various materials in the measurement room. We discriminated true events due to the low-energy (n,n) and/or (n,n′) reactions from the neutron background and the high-energy γ-rays background from the 7Li(p,γ)8Be reaction with a pulse-height selection and a time-of-flight method, and thus obtained a background-subtracted neutron spectrum with a good signal-to-noise ratio. The use of the four detectors of the same size was crucial to construct the new system with high reliability, since we could compare the background-subtracted events taken by one detector with those of other detectors to minimize any possible systematic uncertainties contained in the events. Through detailed studies of the neutron background and of the 186Os(n,n)186Os and 197Au(n,n)197Au reactions, we could show the high sensitivity of the present system.