Neutron spectra from Neutron Standards Laboratory (LPN/CIEMAT) sources with two Bonner sphere spectrometers

Abstract The Neutron Standards Laboratory (LPN: Laboratorio de Patrones Neutronicos) of the Ionizing Radiation Metrology Laboratory (LMRI) of the CIEMAT (Centro de Investigaciones Energeticas Medioambientales y Tecnologicas) has two calibration neutron sources, 241 Am-Be and 252 Cf. Studies to verify the shielding of the facility and to characterize the neutron field in the irradiation room have been carried out using Monte Carlo methods. However, spectral measurements were not performed yet. In this study, we measured the total and direct neutron spectra of both calibration neutron sources. Two different Bonner Sphere Spectrometers (BSS) systems were allocated to 115 cm from the sources, on the calibration bench, with and without the shadow cones (SC). From the count rates obtained with both BSS systems (BSS- 6 LiI and BSS- 3 He), the total neutron spectrum and direct neutron spectrum were unfolded. Total and direct spectra obtained for the 241 Am-Be and 252 Cf sources with the MCNPX and different BSS systems, unfold codes and response matrices presented similar shape and are consistent with each other.