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MEASUREMENT OF IONIZING RADIATION

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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MEASUREMENT OF IONIZING RADIATION

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  1. MEASUREMENT OF IONIZING RADIATION

  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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