Transcript Instruments for Radi..

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.