Author(s): T Yamashita, Yasuno Y, Ikedo M
Lithium or sodium doped beryllium oxide, BeO(Li: 0.5 mol%) and BeO(Na: 0.5 mol%), were found to be efficient and reliable thermoluminescent phosphors. Glow curves of both BeO(Li) and BeO(Na) have simple peaks at 180[degrees]C. The thermoluminescent spectrum shows a broad band in the ultra-violet region peaking at 330 mmicro with shoulders near 300 and 390 mmicro. Besides featuring the characteristic that this material has a photoelectric absorption equivalent to that of biological tissue, the main characteristics of the phosphors, from the point of view of dosimetry include: (1) Exposure response of BeO(Li) is linear from 1 mR to 500 R, and that of BeO(Na) is linear from 2 mR to 100 R. (2) Fading of BeO(Li) is less than 20% within the first hour and 8% within the following 30 days, and that of BeO (Na) is less than 10% within the first hour and 5% within the following 30 days. Light fading of gamma-ray exposed BeO(Li) and BeO(Na) is less than 10% for a light exposure of 300 lux for 10 min. (3) After repeated use, easy annealing (heating at 450 ~500[degrees]C for 1 ~ 10 min) removes the residual dose. (4) The thermoluminescent efficiency remains unchanged after more than 100 cycles of repeated exposure-readout operations. (5) A small amount of tribo-thermoluminescence is emittable; about 15 mR dose equivalent for dropping 10 times from a height of 1 m to concrete floor.