Thermoluminescence and radiation damage in bismuth germanate

Abstract

Bismuth germanate (Bi₄Ge₃O₁₂ or ‘BGO’), primarily because of its higher detection efficiency, is beginning to replace NaI(Tl) as a scintillator for detection of γ rays in several applications, including large electromagnetic calorimeters for high-energy physics experiments¹, computed tomography systems in medical physics² and γ-ray spectroscopy measurements in oil-well logging³. Although the use of BGO is increasing, the scintillation mechanism which converts incident γ-ray energy into visible light is not well understood and its efficiency (light output per unit energy of absorbed γ radiation) decreases following exposure to ultraviolet light or other radiation⁴. We have found that this ultraviolet ‘radiation damage’ is accompanied by a corresponding increase in a stored thermoluminescence signal—the first reported observation of thermoluminescence in BGO. Comparison of scintillation efficiency and thermoluminescence intensity following various exposures to ultraviolet light and after thermal annealing indicate a strong correlation between the scintillation efficiency and the electron population of the thermoluminescence traps. This should be a useful probe for investigating the scintillation mechanism of BGO.