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Instruments for Radiation Detection and Measurement Lab # 3 (1) • In nuclear medicine it is important to ascertain the – Presence – Type – Intensity – Energy of radiations emitted by radionuclides • Two commonly used devices – Gas-filled detectors – Scintillation detectors Gas-Filled Detectors • The operation of a gas-filled detector is based on the ionization of gas molecules by radiations, followed by collection of the ion pairs as current with the application of a voltage between two electrodes. • The measured current is primarily proportional to the applied voltage and the amount of radiations. collection of the ion pairs as current with the application of a voltage between two electrodes ionization of gas molecules by radiations The measured current is primarily proportional to the applied voltage and the amount of radiations. • The two most commonly used gas-filled detectors are •At higher voltages 1000 to 1200 V, – Ionizationfrom chambers counters used becomes forfrom measuring high the current •At• Cutie-Pie a lower voltages 50 to intensity radiation sources, such as output identical regardless 300from V, only the primary ion of x-ray machines how many ion pairs pairs formed by the initial • Dose calibrators measures the activityare of radiopharmaceuticals produced by the radiation are collected. incident radiation. – Geiger-Müller (GM) counters. Dose Calibrators • one of the most essential instruments for measuring the activity of radionuclides – Cylindrically shaped – Sealed chamber with a central well – Filled with argon and traces of halogen at high pressure Geiger-Müller (GM) Counters • One of the most sensitive detectors Scintillation Detecting Instruments • g-ray detecting equipment • Most commonly used: – well counters – Thyroid probes – g or scintillation • All these instruments are g-ray detecting devices • Consist of: • Collimator (excluding well counter) • Sodium iodide detector • Photomultiplier tube • Preamplifier • Pulse height analyzer • Display or Storage • Scintillation detectors consist of scintilator emitting flashes of light after absorbing gamma or x radiation. The light photons produced are then converted to an electrical pulse by means of a photomultiplier tube. The pulse is amplified by a linear amplifier, sorted by a pulse-height analyzer and then registred as a count. Different solid or liquid scintillators are used for different types of radiation. In nuclear medicine, sodium iodide solid crystals with a trace of thallium NaI(Tl) are used for gamma and x ray detection. The light photons will strike the photocathode of a g rays from a source interact in the sodium iodide photomultiplier The pulse is first amplified by a preamplifier and then by a linear amplifier detector and light photons are emitted. (PM) tube and a pulse is generated at the end of the PM tube.