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Instruments for Radiation Detection and Measurement

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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 ... – PowerPoint PPT presentation

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Title: Instruments for Radiation Detection and Measurement


1
Instruments for Radiation Detectionand
Measurement
  • Lab 3 (1)

2
  • 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

3
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.

4
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
5
  • 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.

6
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

7
Geiger-Müller (GM) Counters
  • One of the most sensitive detectors

8
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

9
  • 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.

10
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
11
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