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Nuclear Medicine Instrumentation 242 NMT

Nuclear Medicine Instrumentation 242 NMT. Dr. Abdo Mansour Assistant Professor of radiology E-mail : a_mansour@inaya.edu.sa. Lecture No. 3 Gas detectors. Gas-Filled Detectors. Theory of Operation

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Nuclear Medicine Instrumentation 242 NMT

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  1. Nuclear Medicine Instrumentation 242 NMT Dr. AbdoMansour Assistant Professor of radiology E-mail : a_mansour@inaya.edu.sa

  2. Lecture No. 3Gas detectors

  3. Gas-Filled Detectors • Theory of Operation • Gas-filled detectors function based on measuring the ionization that radiation produces within the gas.

  4. Charges behavior

  5. Gas-Filled Detectors, cont. • The operation of a gas-filled detector is based on the ionization of gas molecules by radiation, followed by collection of the ion pairs as current with the application of a voltage between two electrodes. • The measured current is proportional to the applied voltage and the amount of radiations.

  6. Schematic diagram of a gas filled detector.

  7. Gas-Filled Detectors, cont. • As a result when the radiationinteracts with a gasatom the electron will move towards the positive electrode and the ion will move towards the negative electrode.

  8. Note: • There are several types of detectors that operate on this general principle, but they differ greatly in the details of construction and in the manner in which the radiation-produced ionization.

  9. Principles of Measurement 1- Charge Flow (Measuring Current) • A related approach is to measure the flow of the chargesthat ionizing radiation produces in a gas-filled detector. • The ions (positive charges) produced by the radiation are charged particles • Also, The free electrons (negative charges) produced by the radiation.

  10. Finally: The gas-filled detector has both a positive charges attracted to negative electrode and negative charges attracted to positive electrode.

  11. A- Ionization Chamber

  12. Ionization Chamber is the gas-filled detector has both a positiveand a negativeelectrode.

  13. The ionization chamber consists of a gas-filled detector energized by a relatively low dc voltage. • We will first of all make an estimate of the voltage pulse height generated by this type of detector.

  14. The positive and negative ions produced in the gas by the radiation move in opposite directions, positive ions toward the negative cathode and the negative ions toward the anode. • This movement of ions (charges) is an electric current, which can be detected by a sensitive meter.

  15. The current between the electrodes is a measure of the amount of incoming radiation. • The ionization chamber, is a practical instrument that functions in this way.

  16. B- Geiger counter

  17. Geiger counter • The Geiger counter is an example of Counting Pulses of Current . • The rate at which counts occur in such detectors is a direct measure of the amount of incoming radiation.

  18. The process of ionization, collection of the charges produced, and recording of the count takes place very quickly. • Time is required for the ions to reach their respective electrodes and for the detector to detect on radiation is very low.

  19. Penetration radiation and non-penetration radiation (i. e. Gamma ray has high penetration)

  20. Thank You for your Attention

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