Assessment of LaBr3(Ce) scintillators system for measuring nuclear resonance fluorescence excitations near 2 MeV

Nuclear resonance florescence (NRF) is a powerful tool for non-destructive assaying of nuclear materials. Detection system is a key issue for investigating nuclear materials using this technique. For a long time, Ge detectors were used because they have an excellent energy resolution but also have drawbacks of high cost and slow response time. On the other hand, LaBr₃(Ce) detectors have high response speed and high detection efficiency as well as easy for assembly. However, a drawback of LaBr₃(Ce) crystals comes from the unavoidable internal background levels near 2 MeV. This regime has great importance because it is very rich with ²³⁵U and ²³⁹Pu levels. We tested two different volume scintillators with 2.13 MeV quasi-monochromatic gamma-ray beam from the laser Compton backscattering (LCS) in National Institute of Advanced Industrial Science and Technology (AIST). We could clearly detect the NRF excitation level from ¹¹B at 2.13 MeV. For this level, the energy resolution for the small LaBr₃ (Ce) detector was 1.8% (FWHM), and 2.4% (FWHM) for the large LaBr₃(Ce) detector. Potential of this scintillator for non-destructive assay of nuclear material identification is discussed in the light of our results.