Measurements of high energy neutron spectra with a bonner sphere extension (BSE) measurement system

In our current work, the MCNPX code was used to investigate design modifications to increase the high- energy neutron response of the standard Bonner spheres with cost as a consideration. The system selected uses the existing commercially available BSS as a basis and then extends it by adding concentric shells of Cu, Pb, and W which are used in various combinations with the existing spheres. The design incorporates passive and active detection techniques, namely ¹⁹⁷Au activation foils and the standard Ludlum ⁶LiI(Eu) scintillator. The modeled BSE was fabricated and tested at LANSCE facility. The additional detector spheres provide a more accurate measure of the neutron spectra in the energy regions above 10-MeV than the BSS system alone. Overall, the BSE system investigated herein has been found to be a versatile high and low flux detector having sensitivity over 13 decades in energy while maintaining a nearly isotropic angular response. An inexpensive Bonner Sphere Extension to an existing BSS has been successfully used to measure high-energy neutron spectrum. This system can be used for various measurement applications.