Polycrystalline Bismuth Filters for the Filter Analyzer Neutron Spectrometer (FANS)

摘要

This planned cooperation stems from a research project that aims to fill a requirement for polycrystalline Bismuth filters for application in the Filter Analyzer Neutron Spectrometer (FANS) that is currently installed at BT4 in the NCNR. The size and shape of the desired filters is a straightforward geometric matter, best described by a truncated pyramid with a 2 fold axis (unlike Cheops, which has a 4-fold axis and is not truncated). There is no final design available, but the path to that, however time consuming, is straightforward. The currently adopted fabrication method is cold pressing of granular Bismuth, which considering the melting temperature of Bismuth - in metallurgical terms - is probably close to a "hot" process, thus opening up the possibility that recrystallization takes place at room temperature. The base materials utilized: 200 mesh powder, 100 mesh powder, and water quenched maggot shaped/sized granules. All base metals are specified to be 99.9% bismuth or better.