Title: Instruments for Radiation Detection and Measurement
1Instruments for Radiation Detectionand
Measurement
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
3Gas-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.
4collection 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.
6Dose 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
7Geiger-Müller (GM) Counters
- One of the most sensitive detectors
8Scintillation 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.
10The 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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