Performance of B-CTMFD Detector Vs Ludlum 42-49B, Fuji NSN3 Detectors for Fission Energy Spectrum Neutron Detection with the Source within Lead/concrete Shielded Configurations

Abstract

This paper presents the results of neutron detection efficiency and dosimetry between a borated centrifugally tensioned metastable fluid detector (B-CTMFD) vs He-3 Ludlum-42-49B, and, the Fuji NSN3 conducted using a Cf-252 neutron source behind lead and concrete shielding. MCNP code simulations accounted for 3-D effects and derived cpm/mic.Sv/h factors. Ludlum and NSN3 offer fixed sensitivity, but CTMFD offered on-demand sensitivity by varying its Pneg state between 0.3-0.7 MPa. The B-CTMFD demonstrated sensitivity of up to ~22x greater than Ludlum and 5x greater than NSN3, for 0-15 cm Pb shielding, and 0-30 cm concrete shielding; it overcomes the 60% detection penalty inherent in the NB-CTMF-designed only to detect fast-energy neutrons - as described in the companion (Part-1) paper. Unlike the NB-CTMFD, which used 100% DFP (C5H2F10), the B-CTMFD requires the use of an azeotropic mixture of DFP, methanol, and tri-methyl borate (TMB - using natural boron) in 80:4:16 proportion. The B-CTMFD was about 6 times more sensitive than NB-CTMFD under the most heavily shielded condition and taken together, also offered 2-energy bin neutron spectroscopic enablement, together with 22-5x higher absolute efficiency- relative sensitivity compared with the non-spectroscopic Ludlum (He-3) and NSN3 (methane-nitrogen) based detectors. From an intrinsic efficiency standpoint, the B-CTMFD operating at Pneg = 0.7 MPa state, demonstrated even superior ~103x higher intrinsic efficiency over Ludlum and NSN3.