Workers should take extreme care when approaching high radiation areas, such as areas neighboring highly radioactive equipment or spent fuel pool, due to the risks of radiation exposure. To detect the radiation levels in those areas, it is necessary to develop a remote radiation detection system. The radiation levels surrounding the spent fuel pool are generally measured using the fixed type radiation detector system. Sometimes, the radiation levels on the water surface of the pool need to be measured using a portable radiation detector that a worker brings to the measurement point.
The LYSO crystals have intrinsic radioactivity due to the Lu-176 isotope. 176Lu is a beta-emitter primarily decaying to an excited state of 176Hf. This isotope emits gamma photons with energies of 307 keV, 202 keV, and 88 keV. The crystal’s self-emission causes the crystal to be excited and produce scintillation light. This results in a self-count of 39 cps/g. From this, it was evaluated that the intrinsic radioactivity included in the LYSO scintillator used in this study contributed to 8~10% of the total counts.
Reviewing all the measurements shows that the differences in the detection efficiencies of the fiber-optic sensors were due primarily to the geometrical arrangements of fiber-optic sensors and radiation source and polishing of the fiber-optic sensors and the connecting conditions between the scintillator and transmitting fiber. The polishing of LYSO scintillator and transmitting and the connection between them were manually performed.
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