CLLBC Scintillation Detector Gamma-Ray and Neutron Response Characterization: For Tagged Neutron Time-of-Flight Measurements

Sammanfattning

Scintillation detectors from the elpasolite crystal family were recently developed and made commercially available. One such material is the dual-mode scintillator CLLBC (Cs2LiLaBr4.8Cl1.2:Ce), capable of measuring both gamma rays and neutrons. The neutron detection capability spans from thermal energies up to about 10 MeV, making these detectors suitable for measurements of prompt fission neutrons. In this master's thesis, the first comprehensive characterization of CLLBC detectors is performed by determining calibration functions, energy resolutions, intrinsic timing resolutions, and gamma-ray and neutron detection efficiencies. Furthermore, the pulse shape discrimination capability of CLLBC is investigated for gamma-neutron discrimination. Tagged neutron time-of-flight measurements are conducted on 241Am9Be, by coincident detection of the 4.44 MeV gamma-ray in LaBr3 detectors and the neutron in CLLBC detectors. Three CLLBC detectors were characterized, in addition to three LaBr3:Ce and two LaBr3:Ce,Sr for comparison. For the best-performing CLLBC detector, the results indicate an energy resolution of 3.7% at 662 keV and an intrinsic timing resolution (full-width-at-half-maximum) of 1.2 ns above 1 MeV using 60Co. Moreover, a gamma-neutron separation figure-of-merit of 2.7 is obtained. Neutron detection efficiencies in the region 2-6 MeV are determined to be about 0.2% for the 6Li(n,t)4He reaction and about 1% for three types of (n,n') reactions. Two of the three investigated CLLBC detectors exhibit an energy peak asymmetry, resulting in worse performance, indicating scintillator material quality issues, and motivating further investigation. Future studies are anticipated using a prompt fission neutron spectrum for determining the neutron efficiency at a wider range of neutron energies.