利用鋁階模擬X光管的制動輻射能譜

Using an Al Step Wedge to Simulate the Brmesstrahlung Radiation Spectrum of X-rays

俞勝正(Sheng-Cheng Yu) ； 許昭興(Chao-Hsing Hsuch)

《中華放射線技術學雜誌》 29卷1期 (2005/06) Pp. 39-48

https://doi.org/10.30045/CJRT.200506.0005

摘要

欲了解X光機X光射束的特性，能找出其能譜的分布是最理想的，一般常見求能譜的方式為：使用閃爍偵測器或半導體偵測器，但由於偵測器本身無感時間的問題，入射事件發生率不能太高，克服的方式通常是將射源與偵測器的距離拉大，儀器設備(包括光闌)的擺放是一個很大的技術困擾，本文使用片匣記錄穿透標準鋁階的X光，藉由底片OD值的分布利用電腦計算尋找出最恰當的X光制動輻射能譜，此方法雖然只適合模擬制動輻射的部分尚未能得到特性輻射的分布，但由於模擬計算的結果，不管是制動輻射的分布圖或是管電流、管電壓與劑量的關係，均與教科書內所陳述的已知事實相近，因此當所要探討的事項其特性輻射並非重要影響因子時，利用鋁階配合電腦模擬計算求取X光能譜是一個簡單又可行的辦法。

關鍵字

能譜 ； 制動輻射 ； 可用射束 ； OD值 ； 模擬 ； 曲線擬合

並列摘要

To know the quality of an X-ray beam produced by an x-ray machine, the best method is to check the energy spectrum of the x ray beam. Usually, scintillation detector and semiconductor detector are used to measure the distribution of the energy flux density. But the dead time of detectors has a problem that event rates can not be too high. To avoid dead time information be lost, the distance between source and detector must be wide! However, it is very difficult to determine the accurate position of source and instrument (including diaphragm). In this paper, detector is replaced by an Al step wedge and cassette. When an Al step wedge is irradiated by X-ray, the amount of X-ray transmitted through each step of the Al step wedge are recoded by screen-film. The optical density (OD) produced on a film is measured using a densitometer, utilize the computer to simulate the bremsstrahlung radiation spectrum which can fit the OD values of the film. Although this method is suitable for bremsstrahlung radiation simulation, not for characteristic radiation, but the result of computer simulation is similar to the result stated in textbooks, such as, the spectrum of bremsstrahlung radiation or the relation between dose and tube current and tube voltage. When the influence of characteristic radiation can be negligible, it is a simple and feasible method to utilize an Al step wedge cooperated with computer simulation to get the energy spectrum of x-rays!

並列關鍵字

energy spectrum ； bremsstrahlung radiation ； useful beam ； optical density ； simulation ； data fitting