The standard branching ratio ¹⁰B(n, α₀) to ¹⁰B(n, α₁)

Abstract

The ¹⁰B(n, α) standard cross sections have received considerable attention in recent years due to their relatively poor database available at higher incident neutron energies (above 100 keV) and the problems they caused in the ENDF/B-VI standards evaluation process. In view of a forthcoming new evaluation of the standard cross sections and the demand from the standards sub-group of the WPEC, IRMM has conducted a new measurement of the branching ratio.

A Frisch gridded ionization chamber has been used as detector to measure the α-particles from the reaction. The advantage of this set-up is the nearly full coverage of the 2π angular cone. The ¹⁰B-samples (~30 μg/cm²) have been prepared by our sample preparation group. Our GELINA white spectrum neutron source has been used to deliver the neutrons in the energy region from eV to 1 MeV.

The preliminary data analysis seems at a first glance to be in better agreement with the ENDF/B-VI evaluation than with the most recent measurement of the branching ratio by Weston and Todd. Also the angular distribution has been measured over the full neutron energy range showing strong fluctuations of the anisotropy for the first exited state transition ¹⁰B(n, α₁γ) above about 300 keV incident neutron energy.

Keywords:

• boron 10
• branching ratio
• angular distribution