FANT is the acronym of Enhanced Thermal Neutron Source (Fuente Ampliada de Neutrones Térmicos, 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是增强的热中子源（的缩写˚F uente甲mpliada德Ñ eutrones Ť érmicos，西班牙文）。这是一个高密度聚乙烯减速剂和同位素中子源的平行六面体盒。减速器具有圆柱形的辐射室，在辐射室中获得了相当均匀的热中子通量。FANT设计以前已经过优化，中子光谱是通过MCNP6.1代码通过蒙特卡洛计算来估算的。为了检查FANT热中子场的特性，已使用装有⁶个小⁶的Bonner球光谱仪在辐照室内的参考点进行了测量。LiI（Eu）热中子探测器。为了展开中子谱，使用具有UTA4响应矩阵和NSDann Ver 4.0代码的BUNKIUT。已经发现了一些问题，并提出了有关在狭窄空间内使用大型BSS的建议，以及有关NSDann代码展开此类光谱的能力的建议。但是，结果证实，FANT中的缓和过程非常有效，并且可以获得有用的热中子注量速率。