Development of single-exposure, multidetector neutron spectrometers: the NESCOFI'at'BTF project

NESCOFI'at'BTF is a 3-y project (2011-13) supported by the Scientific Commission 5 of INFN (Italy). The target is the development of neutron spectrometers similar to the Bonner spheres, in terms of response energy interval and accuracy, but able to determine the neutron spectrum in only one exposure. These devices embed multiple (10 to 30) thermal neutron detectors (TNDs) within a single moderator. Two prototypes, called Spherical Spectrometer (SP2) and cylindrical spectrometer (CYSP), have been set up. Whilst SP2 has spherical geometry and nearly isotropic response, the CYSP has cylindrical geometry and is intended to be used as a directional spectrometer. Suitable active TNDs will be embedded in the final version of the devices. The resulting instruments could be used as real-time neutron spectrometers in neutron-producing facilities. This communication describes the design criteria, numerical analysis, experimental issues, state-of-the-art and future developments connected with the development of these instruments. Two prototypal single-moderator neutron spectrometers, called SP2 and CYSP, were designed in the framework of the INFN project NESCOFI'at'BTF. They are intended to be used as isotropic or directional spectrometers, respectively. At present, the SP2 response matrix was tested with passive detectors, whilst the active version of the instrument is under fabrication. In contrast, the active CYSP is available and its response matrix was partially tested with an Am-Be source, obtaining a very satisfactory agreement. A full test of the CYSP response matrix, using reference neutron fields, is planned before the end of 2013. After the active version of both SP2 and CYSP will be set up and tested, these real-time on-line spectrometers could be replicated and distributed to third-party institutions under collaboration agreement. (authors)