Performance of NB-CTMFD Detector Versus Ludlum 42-49B, and Fuji NSN3 Detectors for Hard (Am-Be) and Soft (Cf-252 Fission) Energy Spectra Neutron Sources Within Lead/Concrete Shielded Configurations

Abstract

This paper presents results of neutron detection efficiency and dosimetry between a non-borated centrifugally tensioned metastable fluid detector (NB-CTMFD) configured to detect fast (>0.1 MeV) vs. He-3 based Ludlum-42-49B and the Fuji NSN3, detectors behind various levels of lead and concrete shieldin-together with MCNP code simulations to account for 3-D effects and to relate the detection sensitivity with the dose rate. The MCNP results for neutron energy spectra were validated vs. experimental measurements using the H*TMFD. While Ludlum and NSN3 operate at a fixed sensitivity, the NB-CTMFD detector offers variable sensitivity by varying the tensioned metastable negative pressure (Pneg) from 0.3 MPa to 0.7 MPa. The NB-CTMFD (configured for fast: > 0.2 MeV neutron detection) offered relative sensitivity enhancements of up to 15x greater than the Ludlum and ~5x greater than the NSN3 detector for low shielding thicknesses. For larger thicknesses, the advantage factor for NB-CTMFD unit reduces with increased fast neutron removal via down-scattering, which benefits the Ludlum and NSN3 detectors. Our companion paper compares performance with a Cf-252 spectrum using a borated CTMFD (covering dual energy bins: thermal-epithermal and fast energy ranges) wherein, it is demonstrated that the advantage factor for the CTMFD (if borated) remains elevated at the 5-10x higher level for low and large shielding thicknesses and soft and hard neutron spectra.