Improved multisphere spectrometer system

Shonka Research Associated undertook a research program to improve the capabilities and ease of use of the Bonner sphere spectrometer system. Two key elements formed the heart of this research: replacement of the lithium iodide [LiI(Eu)] detector normally used in the spectrometer system with a spherical boron triflouride (BF3) proportional counter and exploitation of an optimized set of nested polyethylene spheres, including boron-loaded spherical shells. Use of a spherical BF3 detector offers many advantages over the LiI(Eu) crystal. The BF3 detectors are insensitive to gamma radiation. Lack of gamma sensitivity permits acquiring data with simple electronics and allows determination of neutron spectra and dose in lower neutron-to-gamma ratio fields, including background terrestrial radiation fields. The importance of the lack of gamma sensitivity is underscored by the pending changes in neutron quality factors. The nearly perfect spherical symmetry offers advantages for BF3 over LiI(Eu) detectors as well. A light pipe, which perturbs measurements, is not needed. The bare BF3 detector response is not affected by the moderation of neutrons as is the case of the organic light pipe used with LiI(Eu). The spherical symmetry permits the use of smaller diameter shells, which add to the number of response functions