Characterization of CLLBC scintillation detector response to γ-rays and neutrons

The dual-mode elpasolite scintillation material CLLBC ($\mathrm{Cs}$ ₂ $\mathrm{LiLaBr}$ _4.8 $\mathrm{Cl}$ _1.2:Ce) is capable of measuring both $\gamma$-rays and neutrons. The neutron detection capability spans from thermal energies up to about 10 MeV, making these detectors attractive options for studying prompt fission neutron spectra (PFNS). In this work, a comprehensive characterization of CLLBC detectors is performed. Three CLLBC detectors were characterized, in addition to three $\mathrm{LaBr}$ ₃:Ce and two $\mathrm{LaBr}$ ₃:Ce,Sr for comparison. For the best-performing CLLBC detector, the results indicate an energy resolution of 3.7% at $E_{\gamma }=662$ keV and an intrinsic timing resolution of 1.2 ns (FWHM) above $E_{\gamma }=1\mathrm{MeV}$ using ⁶⁰Co. A $\gamma$-neutron separation figure-of-merit of 2.7 is obtained by means of pulse-shape discrimination. Tagged neutron time-of-flight measurements were conducted using a ²⁴¹Am⁹Be neutron source, by coincident detection of the 4.44 MeV $\gamma$-ray and the neutron, to determine the intrinsic neutron detection efficiency between 2–6 MeV. Neutron detection efficiencies of about 0.2% for the ⁶Li(n,t)⁴He reaction and 1% for three types of (n,n′) reactions were obtained. Two of three investigated CLLBC detectors exhibit an energy peak asymmetry, resulting in worse performance, indicating scintillator quality issues and motivating further investigation. Future studies are anticipated using the ²⁵²Cf(sf) prompt fission neutron spectrum to determine neutron efficiencies for a wider range of neutron energies. Although observed in a previous study, neutron detection via ³⁵Cl(n,p)³⁵S was not identified in this work but is planned to be determined using quasi-monoenergetic neutrons generated at the JRC MONNET facility.