Radiation Detection SYSTEM Flashcards
– material that produces signal as a result of energy deposition
-Electrical Charge
• Light
• Chemically change molecules
Detector
– emission of visible light by inorganic crystals and some organic molecules
Radioluminescence
– measures absorbed dose or absorbed dose rate
Dosimeter
- signal is proportional to energy of photon or particle
Spectrometer
– counts number of particles or photons interacting with
detector
Counter
2 types of Detectors
GAS FILLED DETECTORS
SCINTILLATION DETECTORS
___DETECTORS - those that depend on
excitation.
SCINTILLATION
DETECTORS - Those that depend on ionization in which ionization is translated into electric current or impulses
GAS FILLED
Detectors
➢ Radiation is sensed by detecting the ionization of gas
molecules produced by deposition of energy
Gas – Filled
One important approach to radiation detection is the use of an
ionization chamber.
. A ___ is created between two electrodes, but no current flows in the absence of exposure of the chamber to radiation
potential difference
Gas- Filled Detetors- Commonly used gases: ___, ___, ___, ___
Helium, Neon, Argon, and Hydrogen.
Gas – Filled Detectors
➢ The interaction of ionizing radiation with the gas in the chamber creates ___,&___, which move to the electrodes and produced
electrical curren
positive and negative ions
3 Types Of Gas-filled
Detectors
- Proportional Counters
- Ionization Chamber (IC)
- Gieger-Mueller Counters
•Are very sensitive type of personnel
monitoring device
•Provides an instantaneous reading, but must
be recalibrated daily
•Capable of only a predetermined range
•Resembles a fountain pen
•Inside the dosimeter is an ionization chamber
•Normally used only in emergency situation
(diagnostic) in which an immediate reading is
necessary
POCKET DOSIMETERS or Pen Dosimeter
(Gas-filled Detector)
❖ Used to determine the amount
of radioactivity in syringes or
vials
Dose Calibrator
do not have wide application in clinical nuclear medicine.
They are used in research to detect alpha and beta particles
Proportional Counters
One characteristic of proportional counters that makes them particularly useful is their ability to distinguish______
between alpha and beta radiation.
(Gas-filled Detector)
❖ an instrument for detecting and measuring the
intensity of ionizing radiation
❖ Used as a survey meter
Geiger-Mueller Counter
is used for contamination control in nuclear medicine laboratories. They are not particularly useful as dosimeters because they are
difficult to calibrate for varying condition of radiation.
Geiger counter
is one of the example of GM counter.
Survey meter
✓ When ionizing particles passthrough
certain crystals, flashes of light or
scintillation is emitted.
✓ The amount of light emitted is
proportional to the amount of energy
absorbed by the material.
Scintillation Detectors
This type of detectoris the most
commonly used detectorin nuclear
medicine.
Scintillation Detectors
Two Non-imaging devices They are based on the scintillator.
- Routinely used in the nuclear
medicine clinic
- Well Counter
- thyroid probe
Consist of a NaI-crystal with a hole drilled on it.
Measures very small amounts of radioactivity
(kBq)
Used for both radiation protection and clinical protocols
Used to test for small amounts of removable
radioactivity from working surfaces where
radioactivity has been handled or from the
sealed sources. (e,g. calibration sources
Well Counter
THYROID PROBE:
Consist of a ___ on a stand with the
associated counting electronics
The patient is administered a small amount of
___.
Probe: placed at a certain distance from the
thyroid.
Iodine Thyroid Uptake: can be estimated from the
measurements.
NaI-crystal
radioactive iodine
A special piece of equipment used to transform
gamma rays into images that provide
information about the function, primarily, and
anatomy of the organ system being studied.
Gamma Camera
• A device capable of acquiring nuclear medicine
images in various formats
Gamma Camera
• A device that uses the emission of light from a
crystal struck by gamma rays to produce an
image of distribution of radioactive material in a
body organ.
Gamma Camera
Gamma Camera
___
Introduced by ___
Year:
Scintillation or Anger Camera
Hal Anger
(1958)
Gamma Camera System:
Collimator
b. Scintillation crystals
c. Light pipes
d. Photomultiplier tube
e. Pulse Height Analyzer
• Is an electronic device used to determine which portion of the detected spectrum is used to create images.
Pulse Height Analyzer(PHA)
Required to determine the directionality of the
detected event.
Defines the geometric field of view of the
gamma camera crystal
Used to confine the elements of a beam within
an assigned solid angle
Shielding device used to limit the angle of the
entry of radiation.
Collimator
Collimator
Composition:
Location:
Lead (Pb)
at the face of the
detectors
4 types of collimator
Pinhole
Multihole
Parallel hole
Converging multihole
The simplest form of collimator
It consist of a single, small hole or
aperture located a set distance (20 cm)
from the surface.
Image Magnification:
a. Occurs if the objects are closer to the
aperture.
b. Important when imaging small objects
with a large FOV
Pinhole
Pinhole Aperture diameter:
4-6 mm
Pinhole Spatial Resolution: determined by the ___
a. Diameter of aperture
b. Distance from both of the object
c. NaI crystal aperture
collimator
This type of collimator provides the best spatial
resolution and the lowest sensitivity of any
collimator used in nuclear medicine
Pinhole
Consist of a very large number of
parallel holes with absorptive septa
between holes. (limiting the amount of
septal penetration to less than of 5%)
Multihole
Most commonly used type
Provides substantiality better
geometric sensitivity compared to the
pinhole collimator because the object
is viewed through many small holes.
Multihole
Hole of multihole shape
Hexagonal
Multihole Thinner septa: required for
those collimators designed for
low energy photons (<___ kEv)
200
No magnification occurs
with this type of collimator
Hole Diameter: 1mm
Hole length: 20 mm
Parallel hole Collimator
Provides both enhanced spatial
resolution and improved
sensitivity.
Used for imaging smaller
objects (similar to pinhole)
using a camera with a large
FOV.
Used to achieve magnified
image with slightly improved
spatial resolution
Converging Collimator
Scintillation crystals Most commonly used in
gamma cameras.
Thallium activated Sodium
Chloride (NaI) Crystal
is the most fragile
component of the gamma
camera
NaI
A sensitive element used to
detect ionizing radiation by
observing the emission of
light photons induced in a
material.
Scintillation detector
: the process in which some crystalline materials emit a
large number of light photons upon absorption of ionizing radiation
Scintillation
Scintillate: to emit light ___
photons
” is the most important type of radiation detector used in nuclear medicine
scintillation detector/counter
A disk optically transparent
material that helps direct
photons from crystals into the
PMT’s.
• A tube-like structure attached to
the scintillation crystals to
convey the emitted light to the
PMT.
LIGHT PIPE
Consist about 60-100
photomultiplier tube
Photomultiplier tube array
an electronic tube that convert light
photons into electric pulses.
PMT
3 parts of PMT
- Photocathode
- Dynode
- Anode (collecting anode
The main difference between a proportional counter and basic
ionization chamber is greater applied voltage between ___
electrodes
is used for contamination control in nuclear medicine
laboratories. They are not particularly useful as dosimeters because they are
difficult to calibrate for varying condition of radiation
Geiger counter
