Abstract
熱發光劑量計CaF2:Tm（TLD-300）對不同輻射類別與能量具有不同的輝光反應特性，且有鑑別輻射類別與能量的能力。為了解其對於能量介於加馬和紫外光的低能量X射線之反應行為，本文係利用位於新竹科學園區中，全世界第三座第三代同步輻射加速器所產生的高強度低能量光子，研究TLD-300對於能量低於9 keV以下光子之回應。由於能量於1.5 keV以下的光子在空氣中衰減很快，因此實驗分成兩部份：一為能量在200至1200 eV之間的光子，於真空中照射；另一為3至9 keV，於大氣中照射。並利用Chen氏峰形法和數值曲線擬合法，進行輝光曲線動力學參數分析。實驗結果顯示，TLD-300對此能量範圍（200 eV至9 keV）的光子之反應行為與對加馬輻射的回應是迥然不同的。當光子對物質之質量衰減係數與能量吸收係數愈大，光子愈易在TLD-300表面處即被完全吸收，並形成以第二輝光峰為主的輝光曲線。其中第二輝光峰靈敏度的提升可用陷阱競爭模型作解釋。動力學參數分析發現，第二輝光峰之陷阱深度與頻率因數皆比第三輝光峰大，但第四輝光峰之陷阱深度與頻率因數為所有輝光峰中的最小者。隨著TLD表面的荷電載體濃度的增加，將會導致陷阱間的交互作用機率大大提升。The CaF2:Tm (TLD-300) has the capability to distinguish thedifferences among various types of radiation and energy withdifferent characteristic of glow curves. For studying theresponses of TLD-300 for low-energy X-ray with energies betweengamma ray and UV, low energy photon with high intensity used inour experiments were generated by the Synchrotron RadiationResearch Center (SRRC) which is located at the Hsinchu Science-Based Industrial Park. Since photons with energies below 1.5keV are seriously attenuated in the air, therefore ourexperiment were divided into two parts: the first part ofexperiment was carried out by irradiating TLDs with 200 - 1200eV photons in vacuum, and the second part with 3 - 9 keVphotons in air. The kinetic parameters were analyzed with theaid of the Chen's method and the computerized glow-curvedeconvolution as well. The experimental results revealed thefacts that the glow curves obtained for low energy photons arequiet different from that irradiated with gamma ray. If theTLD phosphor has larger mass attenuation coefficient and mass-energy absorption coefficient, then the photons are likelyabsorbed on the irradiated surface and form the second glowpeak (P2) in TL glow curves. The increase in sensitivity of P2can be interpreted with the competing traps model. The analysesof kinetic parameters, the trap depths and frequency factorsfor P2 show that they are all greater than those for P3.However, the trap depths and frequency factors of P4 are thesmallest among all the glow peaks. As the concentrations ofcharged carrier on the TLD surface are increasing, the reactionprobabilities between traps are anticipated to increase.