Intrinsic background radiation of LaBr₃(Ce) detector via coincidence measurements and simulations

The LaBr₃(Ce) detector has attracted much attention in recent years because of its superior characteristics compared with other scintillating materials in terms of resolution and efficiency. However, it has a relatively high intrinsic background radiation because of the naturally occurring radioisotopes in lanthanum, actinium, and their daughter nuclei. This limits its applications in low-counting rate experiments. In this study, we identified the radioactive isotopes in the ϕ3 ^{′ ′}× 3 ^{′ ′} Saint-Gobain B380 detector by a coincidence measurement using a Clover detector in a low-background shielding system. Moreover, we carried out a Geant4 simulation of the experimental spectra to evaluate the activities of the main internal radiation components. The total activity of the background radiation of B380 is determined to be 1.523 (34) Bq/cm³. The main sources include ¹³⁸La at 1.428 (34) Bq/cm³, ²⁰⁷Tl at 0.0135 (13) Bq/cm³, ²¹¹Bi at 0.0136 (15) Bq/cm³, ²¹⁵Po at 0.0135 (3) Bq/cm³, ²¹⁹Rn at 0.0125 (12) Bq/cm³, ²²³Fr at 0.0019 (11) Bq/cm³, ²²³Ra at 0.0127 (10) Bq/cm³, ²²⁷Th at 0.0158 (22) Bq/cm³, and ²²⁷Ac at 0.0135 (13) Bq/cm³. Of these, the activities of ²⁰⁷Tl, ²¹¹Po, ²¹⁵Po, ²²³Fr, and ²²⁷Ac are deduced for the first time from the secular equilibrium established in the decay chain of ²²⁷Ac.