Study on the γ + X, γ + β, γ + α Coincidence Summing Effects of the Intrinsic Background Instrument Spectrum of a LaBr₃(Ce) Scintillation Counter

The energy resolution of a LaBr₃(Ce) scintillation counter can reach 2.7% (662 keV) at room temperature. As a radiation measuring device, it has remarkably good characteristics. However, the LaBr₃(Ce) crystal has its own intrinsic radioactivity background, which mainly comes from ¹³⁸La and from ²²⁷Ac and its daughters. ¹³⁸La can emit β, γ and X-rays through β and γ decay; ²²⁷Ac and its daughters can emit α, β and γ-rays through a, β and γ decay. α, β and X-ray energy are characteristic while β-ray energy is continuous. The energy of α, β and X-rays is mainly deposited in the crystal unless the α, β and X-rays at the edge of the crystal can escape from the crystal. Therefore, the α, β, γ and X-rays generated by the intrinsic radioactivity of the crystal are superimposed on the instrument spectrum, which makes the instrument spectrum more complicated and produces the coincidence summing effects of γ + X, γ + β and γ + α.In this research, the GEANT4.9.5 software package was used to simulate the spectra of α, β, γ and X-rays. On the basis of a combination of fitting decomposition and reconstruction, the simulation spectrum of the LaBr₃(Ce) self-radioactive background was obtained accurately and was verified by using physical experiments.