Experimental characterization of FANT, a new thermal neutron source.

FANT is the acronym of Enhanced Thermal Neutron Source (F uente A mpliada de N eutrones T érmicos , in Spanish). This is a parallelepiped box of high-density polyethylene moderator and an isotopic neutron source. The moderator has a cylindrical irradiation chamber where a rather uniform thermal neutron flux is obtained. The FANT design was previously optimized and the neutron spectra were estimated by Monte Carlo calculations with the MCNP6.1 code. To check the characteristics of the FANT thermal neutron field, measurements have been performed at the reference point inside the irradiation chamber with a Bonner sphere spectrometer holding a small 6LiI(Eu) thermal neutron detector. To unfold the neutron spectrum BUNKIUT with UTA4 response matrix and NSDann Ver 4.0 codes were used. Some issues have been found and recommendations are made about the use of large BSS inside narrow spaces, and about the capacity of NSDann code to unfold these kind of spectra. However, the results confirm that the moderation process in FANT is very effective and allows obtaining useful thermal neutron fluence rates. • FANT is a thermal neutron source based on 241Am/9Be source inside HDPE cavity. • Neutrons from a241Am/9Be source are moderated and scattered in the system. • Designed by Monte Carlo to increase the thermal neutron flux. • Bonner Spheres Spectrometer (BSS) used to determine the neutron spectrum. • BUNKIUT (UTA4) and NSDann Ver 4.0 spectral unfolding codes used. [ABSTRACT FROM AUTHOR]