The 10B (n,alpha0)7Li and 10B (n,alpaha1gamma)7Li Alpha-Particle Angular Distributions for En < 1 MeV

The 10B(n,alpha0)7Li and 10B (n,alpaha1gamma)7Li 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. A twin Frisch-grid ionization chamber has been used with two very thin 94% 10B-enriched samples mounted back-to-back on the common cathode. With this type of charge particle detector it is possible to measure the angular distribution of the alpha particles in a close to 2x2p solid angle, with a clear separation of the alpha-particle yields from both reaction channels: alpha-emission to the 7Li ground state {alpha0} and to its first excited state {alpha1}. Hence, for the first time nearly the full solid angle at all incident neutron energies investigated has been covered. A strong angular anisotropy was observed and is discussed in the frame of the compound nucleus reaction mechanism. The alpha-particle center-of-mass angular distributions have been used for calculating the branching ratio 10B(n,alpha0)/10B(n,alpha1gamma). Both data sets were entered into the IAEA Coordinated Research Project on "Improvement of the Standard Cross-Sections for Light Elements" and used for compiling the ENDF/B-VII evaluation data-file for this reaction.

HAMBSCH Franz-Josef;  RUSKOV Ivan; 

2009-08-07

AMER NUCLEAR SOC

JRC41487

0029-5639,