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MEASUREMENT OF IONIZING RADIATION. Measurement of Ionizing Radiation. Objectives Familiarization with Detection Mechanisms Identify the Correct Instrument for the Job. Detection Mechanisms. Gas Filled Detectors Scintillation Semiconductor. Gas Ionization Regions.

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  2. Measurement of Ionizing Radiation • Objectives • Familiarization with Detection Mechanisms • Identify the Correct Instrument for the Job

  3. Detection Mechanisms • Gas Filled Detectors • Scintillation • Semiconductor

  4. Gas Ionization Regions • Pulse Amplitude vs. Applied Voltage • Ion Saturation • Proportional/Limited Proportional • Geiger-Mueller

  5. Pulse Amplitude vs. Applied Voltage GM Ion Proportional

  6. Ion Saturation Detectors • Common Detectors • Pocket Dosimeter • Ion Chamber • Pressurized Ion Chamber

  7. Pocket Dosimeter • Uses Charge Integration • Exposure Readout With Quartz Fiber Electroscope • Gamma/X-ray Only • Inexpensive • Poor Accuracy

  8. Ion Chamber • Directly Quantifies Exposure Rate • Linear Energy Response • Gamma/X-ray/Beta(with window)

  9. Pressurized Ion Chamber • Extremely Sensitive • Gamma/X-ray • High Background • Can be Expensive

  10. Proportional Region Detectors • Common Detector • Gas Flow Proportional Counter

  11. Gas Flow Proportional Counter • Can Integrate Source and Gas • Spectroscopy • Alpha/Beta/Low-Energy Gamma/X-ray • Can be Expensive

  12. Geiger-Mueller Region Detectors • Common Detector • Geiger Tube/G-M Counter

  13. Geiger Tube • Pulse Amplitude Does Not Vary With Initiating Event • Output is Normally CPM • Non-Linear Energy Response • Can be Calibrated in Exposure Units • Alpha/Beta/Gamma/X-ray Depending on Window and Fill Gas

  14. Scintillation • Visible Light Produced After Excitation of a Substance • A Good Scintillator Converts a Large Fraction of Incident Radiation Energy Into Prompt Fluorescence

  15. Scintillation • Zinc Sulfide used for alpha • Plastics and liquids used for Beta • Organic and inorganic crystals for x and gamma • Liquids used for all currently

  16. Scintillation Detectors • Common Detectors • Solid Scintillator • Sodium Iodide, NaI • Thin Crystal NaI • Plastic • Liquid Scintillation Counter

  17. Solid Scintillation Detectors • Thick Crystal Sodium Iodide • Extremely Sensitive • Used for Quantification and Identification • Gamma/High-Energy X-ray Only • Expensive • Poor Resolution

  18. Solid Scintillation Detectors • Thin Crystal Sodium Iodide • Good Sensitivity at Low-Energies • Low-Energy Gamma/X-ray Only • Highly Energy Dependent • High Background

  19. Solid Scintillation Detectors • Plastic Scintillator • Can be made into a Large-Volume Detector • Alpha/Beta/Gamma • Inexpensive • Low Light Output/Self-absorption a Problem

  20. Liquid Scintillation Counting • Sample Integrated With Scintillator • Can be Highly Efficient • Widely Used for Low-Energy Beta Counting • Alpha/Beta • Quenching a Problem

  21. Semiconductors • Electron-hole Pairs Created in a Semiconductor by a Charged Particle Generate the Signal

  22. Solid-State Detectors • Common Detectors • Silicon Diode • Lithium Drifted Silicon • High Purity Germanium

  23. Silicon Diode • Charged Particle Spectroscopy • Superior Energy Resolution • Alpha/Heavy Ions • Limited to Small Sizes • Susceptible to Performance Degradation

  24. Lithium Drifted Silicon • Low-Energy Photon Spectroscopy • Beta/Electron Detection and Spectroscopy • Superior Energy Resolution • Low-Energy Gamma/X-ray/Beta/Electrons • Must be Cooled With Liquid Nitrogen • Susceptible to Performance Degradation

  25. High Purity Germanium Detector • Gamma Ray Spectroscopy • Superior Energy Resolution • Gamma • Must be Cooled with Liquid Nitrogen • Susceptible to Performance Degradation

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