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Introduction to Health Physics Chapter 10 Health Physics Instrumentation

Introduction to Health Physics Chapter 10 Health Physics Instrumentation. Basic principles. Minimizing exposure time Maximizing distance from the radiation source Shielding the radiation source. Basic principles. Time Distance Point source Shielding. Basic principles. Distance

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Introduction to Health Physics Chapter 10 Health Physics Instrumentation

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  1. Introduction to Health PhysicsChapter 10Health Physics Instrumentation

  2. Basic principles • Minimizing exposure time • Maximizing distance from the radiation source • Shielding the radiation source

  3. Basic principles • Time • Distance • Point source • Shielding

  4. Basic principles • Distance • Point source; Example 10.1

  5. Basic principles • Distance • Line Source; Example 10.2

  6. Basic principles • Distance • Plane Source; Example 10.3

  7. Basic principles • Distance • Volume Source

  8. Basic principles • Shielding • underestimates the required shield thickness • a significant number of photons may be scattered by the shield into the detector

  9. Basic principles • Shielding • broad beam and narrow beam attenuation of Co-60 gamma rays by concrete

  10. Basic principles • Shielding

  11. Basic principles • Shielding • When such data are not available, a shield thickness for conditions of poor geometry may be estimated by • The buildup factor, B, which is always greater than 1

  12. Basic principles • Shielding

  13. 主 屏 蔽 次屏蔽 X光機屏蔽 結 構 屏 蔽 防護套管

  14. PROBLEMS

  15. 防護套管：由製造商提供 • 診斷用X光機：診斷型X光管之滲漏輻射在距靶一公尺處，每小時不得超過100毫侖琴。 • 治療用X光機：(<500kV)治療型X光管之滲漏輻射在距靶一公尺處，每小時不得超過1侖琴。(>500kV)治療型X光管之滲漏輻射在距靶一公尺處，每小時不得超過原始輻射在距靶一公尺處之1/1000。

  16. 週工作負荷, W 使用因數, U 曝露, X 管制區或非管制區 最大許可曝露, P 佔用因數, T 結構屏蔽：由使用者設計 穿透率 K=P/X

  17. 佔用因數：間距數少 全部佔用 部分佔用 偶而佔用

  18. 使用因數：只考慮一台機器 X光有用射束(useful beam)朝向某一主屏蔽方向之時間分率

  19. (人)劑量限度 • 年 • 工作人員： 20 mSv/yr • 一般人： 1 mSv/yr • 週 • 工作人員： 0.4 mSv/wk • 一般人： 0.02 mSv/wk

  20. (機)劑量約束 NCRP-147採用之週劑量約束為： 　　管制區：0.1 mSv / wk 　　非管制區：0.02 mSv / wk

  21. 空氣克馬度量位置

  22. 佔用因數：針對最大曝露者 每週時數 40 20 8 5 2 1

  23. PROBLEMS

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