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• Film badges are simple detectors that use photographic film to see the amount of radiation one is exposed to. The darker the film, the greater the radiation exposure.
• These badges, based on the environment will vary in thickness and material to help measure the amount of radiation exposure.
• 2 common forms of detectors – GM tube and scintillation counters. These are complex detectors that detect ioniziation due to radiation.
• The GM tube has wire electrode, glass tube, metal tube and thin window.
• The GM tube works: gas molecules ionized by radiation. Formed electrons attracted to positive wire electrode. Leads to further ionization of electrons. More ionization due to positive ions attracted to cathode. Charged particle cascade lead to short pulse that is amplified and measured. Event occurred.
• Quenching required to detect further events.

  GM tube dead time is known as quenching period. Important as discharge created by single particle. No detection until discharge is stopped.
• Scintillation – absorbing high radiation by certain materials lead to small flashes of light.

  Scintillators – has transparent NaI crystal that fluoresces when hit by radiation.

  PMT (photomultiplier tube) detects and amplifies the flash.

  Original photon energy can be found by knowing intensity of flash.
• When photon reaches the PMT cathode it causes photoelectric effect. Leads to electron ejection from photocathode.
• Photoelectron produced is sent towards first dynode that is coated with material which produces more electrons when hit. This is then sent to the second dynode where more electrons are produced. This is repeated till the electron cascade reaches anode, generating a current pulse. Shows photon detection.
• Scintillation counters used in gamma cameras
• Gamma camera – there is a large flat NaI crystal. Behind crystal there are PMT tubes hexagonally arranged. PMT detect flashes produced from crystal and radiation interaction.  Collimator used to specifically detect photon source. Collimator is thick lead sheet with many holes. Holes allows photons moving in specific direction to hit crystal. Gamma ray detection can be done from analysing which hole the photon is moving through.
• PMT are close together to minimize gaps. Made for detection and amplification of signal. Position logic circuits get the electric signals from tube and figure out where the scintillation event has occurred.
• Radioactive material is given to patient. This is absorbed by studied organ. Gamma camera placed over patient. Gives 2D image of intensity and different parts of the organ absorbed by radioactive material.
• Gamma camera imaging helps for organ function studying.
• Gamma cameras can be used to detect bone disease. Radionuclide given to patient. Higher uptake of tracer in areas affected by dieases. Produces hotspots on gamma camera images. Allows organ damage detection.
• Ideal radionucleide – short half life for minimal exposure.

  Gamma ray emmission with detectable energy. Ensures low dose.

  Non toxic
• Tc-99 is good radionuclides – short half life. Low energy gamma ray emmision. Chemical structure allows incorporation. Flexible tracer.
• Thyroid uses iodine for metabolic rate and hormonal regulation.

  Underactive thyroid takes less iodine.

  Overactive thyroid takes more iodine.
• Adminster radioactive I-123 to patient orally. Measure intensity using scintillation counter. After 24 hours compare standard I-123 to adminstered one. Thyroid counts to standard count ratio gives percentage uptake.

  30-50% normal. Greater than 50% hyperactive. Less than 30% underactive.