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

Abstract

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 138 La and from 227 Ac and its daughters. 138 La can emit β, γ and X-rays through β and γ decay; 227 Ac and its daughters can emit α, β and γ-rays through α, β and γ decay. α, γ 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.

Characterization of a Fiber Optic Radiation Sensor Prototype for Nuclear Dismantling

“…For the investigation of the energy resolution of the measuring system, measurements with radioactive sources of the nuclides 137 Cs and 22 Na were performed by placing the gamma-ray sources next to the sensor. The gamma-ray emission energies of 22 Na are E γ 511 keV of the annihilation radiation of the emitted positrons and E γ 1275 keV and the gamma-ray emission energy of 137 Cs is E γ 662 keV.…”

“…In the measurement where the sensor is placed behind a lead block, only a small amount of scintillation light should be generated. Measurements with both setups are performed with a 137 Cs source with an activity of 21 kBq and a 22 Na source with an activity of 1.0 MBq. Additionally, a background measurement without a radiation source is performed.…”

“…For the measurements with the 137 Cs source and the 22 Na source, the number of background events with the value of N Back 778 is subtracted. Furthermore, the ratio NCe NSc of the estimation of the number of Cerenkov light pulses N Ce to the number of scintillation light pulses N Sc is determined.…”

“…Figure 11: The concrete shielding distance between sensor and 22 Na source with an activity of 1.3 MBq can be estimated from the energy distribution by the shielding distance parameter β. The concrete shielding distance l β is determined with this analysis method from the spectroscopic measurement.…”

“…The described evaluation method was performed for this measurements by using the energy region from 600 keV to 800 keV as the full energy events and the energy region from 200 keV to 450 keV as the energy region of Compton scattered events. Like in the investigation with the 22 Na source a linear dependency of the shielding distance parameter can be implemented for concrete shielding distances from 1.2 cm to 6 cm, which can be seen in Fig. 12.…”