The 10B(n,α0)7Li and 10B(n,α1γ)7Li alpha-particle angular distributions, branching ratios and cross-sections measurements for En <3 MeV

The B-10(n,alpha(0))Li-7 and B-10(n,alpha(1)gamma)Li-7 angular distributions have been measured at the GELINA time-of-flight spectrometer in the incident neutron energy range from 0.1 keV to 1 MeV by means of a twin Frisch-grid ionization chamber. With this type of detector it is possible to measure the angular distribution of the charged reaction fragments in a close to 2x2 pi solid angle with similar to 100% efficiency and a clear separation of both reaction channels: emission to the Li-7 ground state (alpha(0)) or to its first excited state (alpha(1)). A strong angular anisotropy was observed at similar to 520 keV. In order to extend the energy range up to 2.5-3 MeV and to measure, also, the reaction cross sections, a double twin Frisch-grid ionization chamber was constructed. It is loaded with two very thin 94% B-10-enriched samples, mounted back-to-back with U-235 samples on the common cathodes. New data acquisition, visualization and analysis software is used in a new set of long-term measurements, which are still going on.