Development of a compact lanthanoid bromide γ-ray spectroscopy system with high-count-rate pulse processing and simultaneous pulse-current operation mode for in-situ non-destructive assay

A new γ-ray spectroscopy system suitable for use in intense γ-ray fields has been developed. The system comprises a compact LaBr3:Ce scintillator (3 mm × 3 mm × 3 mm), high-speed digital pulse processing, and a square-type photon multiplier tube (PMT) equipped with a transistor-loaded voltage divider circuit to all dynode stages. The relative energy resolution was ≤ 3.6% at 662 keV for dose rates of up to 2.89 Gy h-1 in a 137Cs γ-ray field and was ≤ 4.3% at 1333 keV for dose rates of up to 4.17 Gy h-1 in a 60Co γ-ray field, without the need for heavy-metal radiation shielding. Over a wide range of dose rates, the detector's supply current is more closely proportional to γ-ray intensity than to corrected count rates, suggesting simultaneous pulse-current operation. As a further demonstration, a 4.38 MBq sealed 60Co source was measured under the background γ-ray irradiation by a 137Cs source. Although the geometry between the detector and 60Co source was fixed, the background γ-ray dose rate (intensity) varied. The identification and quantification of the 60Co source remained unaffected at irradiation dose rates of up to 1.04 Gy h-1.