Instruments for Radiation Detection and Measurement

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Instruments for Radiation Detectionand
Measurement

• Lab 3 (1)

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• 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

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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.

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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.
ionization of gas molecules by radiations
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• The two most commonly used gas-filled detectors
  are
• Ionization chambers
• Cutie-Pie counters used for measuring high
  intensity radiation sources, such as output from
  x-ray machines
• Dose calibrators measures the activity of
  radiopharmaceuticals
• Geiger-Müller (GM) counters.

• At higher voltages from 1000 to 1200 V, the
  current becomes identical regardless of how many
  ion pairs are produced by the incident radiation.

• At a lower voltages from 50 to 300 V, only the
  primary ion pairs formed by the initial radiation
  are collected.

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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

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Geiger-Müller (GM) Counters

• One of the most sensitive detectors

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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

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• 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.

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The light photons will strike the photocathode of
a photomultiplier (PM) tube and a pulse is
generated at the end of the PM tube.
g rays from a source interact in the sodium
iodide detector and light photons are emitted.
The pulse is first amplified by a preamplifier
and then by a linear amplifier
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