2. OUT LINES
Abstract.
Introduction.
Scintillation .
Scintillation detector.
Components of Scintillation detector.
Principle of Operation.
Applications of Scintillation detector.
Advantages and disadvantages.
Conclusion.
References.
3. ABSTRACT
The scintillation detector is one of the most often and widely
used particle detection devices in nuclear and particle
physics today.
It makes use of the fact that certain materials when struck
by a nuclear particle or radiation, emit a small flash of light,
i.e. a scintillation. When coupled to an amplifying device
such as a photomultiplier, these scintillations can be
converted into electrical pulses which can then be analyzed
and counted electronically to give information concerning
the incident radiation.
4. INTRODUCTION
In 1903 Sir William Crookes invented the first inorganic
scintillation detector, a Zinc sulfide screen which produced
weak scintillations when struck by alpha particles. 1
These scintillations could be viewed by the naked eye in a
dark room. It was used by Geiger and Marsden in their
experiments with alpha particles.1
Not so practical, fell In disuse with the arrival of gaseous
ionization instruments.1
Then in 1944 Curran and Baker replaced the naked eye with
the photomultiplier tube and revived the use of scintillations.
Still nowadays scintillation detectors are widely used and
highly reliable and conveniently available.1
5. 1.SCINTLLATION
Certain materials, when struck by radiation, emit a
small flash of light, a scintillation.1
2. SCINTTILATION DETECTOR
A device for detecting and counting scintillations
produced by ionizing radiation.2
6. 2.1 SCINTTILATION DETECTOR
COMPONENTS
In general, a scintillation detector consists of:
2.1.1 SCINTILLATOR
2.1.2 PHOTODETECTOR
See figure 1
FIG.1. Scintillation detector
Photodetector
7. 2.1.1 SCINTILLATOR:
is any transparent material that can release a
photon in the ultraviolet or visible-light range, when
an excited electron in the scintillator returns to its
ground state.3 See figure 2.
Types of Scintillator4
FIG.2. Scintillator.
8. CHARACTERISTICS OF INORGANIC SCINTILLATORS
Inorganic scintillators are characterized by high density, high atomic
number, and pulse decay times of approximately 1 microsecond.4
They exhibit high efficiency for detection of gamma rays.
Inorganic crystals can be cut to small sizes and arranged to provide
position sensitivity. This feature is widely used in medical imaging to
detect X-ray or gamma rays.4
Inorganic scintillators are better at detecting gamma rays and X-rays
than organic scintillators. This is due to their high density and atomic
number which gives a high electron density.4
9. CHARACTERISTICS OF ORGANIC SCINTILLATORS
In general, organic scintillators have fast decay times
(approximately 10 nanoseconds).4
Pure organic crystals. This type of crystal is frequently used in
the detection of beta particels.4
liquid organic solutions. Liquid organic solutions are produced
by dissolving an organic scintillator in a solvent.4
Plastic scintillators. Plastic phosphors are made by adding
scintillation chemicals to a plastic matrix. The plastic has a high
hydrogen content, therefore, it is useful for fast neutron
detectors.4
10. 2.1.2 PHOTODETECTOR
A sensitive photodetector (usually a photomultiplier tube
(PMT)), which converts the light to an electrical signal
and electronics to process this signal.3
See figure 3.
FIG.3. photomultiplier tube
11. 2.2 SCINTILLATION DETECTOR – PRINCIPLE OF
OPERATION.
Ionizing radiation enters the scintillator a. This cause
electrons to be raised to an excited state. The excited
atoms of the scintillator material de-excite and rapidly
emit a photon in the visible (or near-visible) light range.
The quantity is proportional to the energy deposited by
the ionizing particle.4
The light strikes the photocathode, releasing at most
one photoelectron per photon(photoelectric effect). Using
a voltage potential, this group of primary electrons is
accelerated and strike the first dynode with enough
energy to release additional electrons.4 see figure 4 FIG.4. Scintillation
Detector
12. These secondary electrons are attracted and strike a second dynode
releasing more electrons. This process occurs in the photomultiplier
tube. Each subsequent dynode impact releases further electrons, and
so there is a current amplifying effect at each dynode stage. Each stage
is at a higher potential than the previous to provide the accelerating
field. Primary signal is multiplied.4
At the final dynode, sufficient electrons are available to produce a
pulse of sufficient magnitude for further amplification. This pulse carries
information about the energy of the original incident radiation. The
number of such pulses per unit time also gives information about the
intensity of the radiation.4
13. scintillation counters can be used to detect alpha, beta,
gamma radiation. They can be used also for detection of
neutrons.3
Radiation protection, assay of radioactive materials and
physics research because they can be made inexpensively yet
with good efficiency, and can measure both the intensity and
the energy of incident radiation.3
Hospitals all over the world have gamma cameras based on
the scintillation effect and, therefore, they are also called
scintillation cameras.3
2.3 APPLICATIONS OF SCINTILLATION DETECTOR
14. ADVANTAGES OF SCINTILLATION COUNTERS
Efficiency and the high precision and counting rates that are
possible. These latter attributes are a consequence of the
extremely short duration of the light flashes, from about 10-9
seconds in (organic scintillators) to 10-6 seconds in (inorganic
scintillators).4
The general ease of sample preparation.4
Ability to detect samples of many types, solid, liquid,
suspensions and gels.4
15. DISADVANTAGES OF SCINTILLATION COUNTERS
High voltage is required.4
A disadvantage of some inorganic crystals, is their
hygroscopicity, a property which requires them to be
housed in an airtight container to protect them from
moisture.4
Background radiation.3
Need for cooling system, because temperature affects
counting efficiency.3
16. CONCLUSION
Scintillation detectors are used to detect all types of
radiation, including gamma ray, electrons, neutrons,
alpha particles, and neutrinos. Efficient detection of these
particles depends on how well and how quickly they lose
energy in the scintillation medium. These factors are
characterized by the stopping power of the material,
which depends not only on the atomic weights of the
material but also on their densities.
17. REFERENCES
1 D.Green, Scintillation detector, WWW Document
( https://www.nbi.dk/~xella/lecture_16Feb2009.pdf)
2 https://medical-dictionary.thefreedictionary.com/scintillation+counter
3 N.cnnor, Scintillation detector detention, WWW Document
( https://www.radiation-dosimetry.org/what-is-scintillation-counter-scintillation-detector-
definition/).
4 F.K.Glenn, Scintillation Counter – Principle of Operation, WWW Document
(https://www.nuclear-power.net/nuclear-engineering/radiation-detection/scintillation-
counter-scintillation-detector/scintillation-counter-principle-of-operation)
ACKNOWLEDGEMENTS
I am thankful to Dr. Issam Ashqar, who has guided me through out
this course and made this project better.
