The study of the miniature plastic scintillating fiber detector ─ A dosimeter for small field radiotherapy application

• Main Authors: Liao Hsin-fa, 廖信發
• Other Authors: Yuan Liq-Ji
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/67004676340468207861

碩士 === 國立清華大學 === 原子科學系 === 90 === The purpose of this study is trying to develop a miniature plastic scintillation fiber detecting system used for radiation measurement. The fluorescence light released promptly from the scintillator under the ionizing radiation exposed, therefore, the dose rate can be evaluated by its intensity of the light emitted. The work of the developed detecting system consists mainly (1) to develop a high impendence of high amplification current amplifier, which could convert the very low current signal into readable voltage output, and (2) to construct the detector of opto-electric device, which the Bicron type BCF-20 plastic scintillating fiber of 1 mm × 5 mm L was used as the detection probe to integrate with a 10 m long plastic optic fiber as the light transmission medium, and the opto-electric converting device was either by a photomultiplier tube or a photodiode. The experiments divided into two groups. One has photomultiplier-coupled of optic fiber system and the other has photodiode-coupled one. Of the group content two different type probe, one was clad with thin sheet of pure gold and the other was bared. The results show the detection sensitivity were no significantly difference between the gold clad and bared one. The photomultiplier-coupled device is suitable to determine the dose rate below 350 cGy/min, and the photodiode-coupled one is suitable only for the dose rate above 5 Gy/min. In small field cone beam experiments, which carried out of the dose profile measurements of different depth in water phantom. Our developed system shows much better performance than the conventional ion chamber, especially in the region of penumbra not only has excellent spatial resolution but also has accurate of dose gradient.