It is about the dosimeters and its working

1. DOSIMETER
DR.JAYAPANDIYAN

2. TOPICS TO BE COVERED
❑ Introduction
❑ Pocket dosimeter
❑ Thermoluminescent dosimeter
❑ Solid state detector
❑Advantages
❑Disadvantages

3. DOSIMETER
▪Dosimeter is an instrument used to
measure and monitor exposure of
ionizing radiation over a period of
time .
▪Radiation exposure is measured in
gray(Gy).
Film badge
TLD BADGE

4. POCKET DOSIMETER
❑ A pocket dosimeter is a small, portable
device used to measure and monitor
radiation exposure in real time.
❑ It measures radiation exposure of x
rays and gamma rays .
❑ Pocket dosimeters are typically
compact and lightweight, fitting easily in
a pocket .
Pocket dosimeter

5. PRINCIPLE
▪Pocket dosimeters works on the principle of ionization to
measure radiation
▪As ionizing radiation passes through the dosimeter, it creates
ions in the surrounding gas.
▪Ionized particles generate an electrical signal proportional to the
radiation level.
▪The signal is amplified and converted into a measurable
radiation dose.

6. Components of Dosimeter
1.Eye piece lens
2.Scale
3.Objective lens
4.Ionization Chamber
5.Movable fiber
6.Bellows
7.Charging Contact pin
8.Clip

7. WORKING
▪The gas filling
The chamber contains a specific gas that is easily ionized by
radiation.
▪Radiation Interaction
Radiation enters the chamber, interacting with the gas and causing
ionization.
▪Electrodes
Electrodes are used to collect ionized particles , creating an
electrical current.

8. STEPS INVOLVED
❑ Exposure
The dosimeter is worn in a pocket or clipped to clothing for
accurate exposure measurement.
❑ Reading
The display shows the accumulated radiation dose, often in units
like mSv.
❑ Calibration
Regular calibration is required to ensure the accuracy of the
device's readings.

9. ADVANTAGES
⮚Compact and Portable
⮚ Real-time reading
⮚Easy to use
⮚Rechargeable and resettable

10. LIMITATIONS
⮚Limited sensitivity for certain types of radiation, such as beta
particles and neutrons.
⮚Accuracy may be compromised by high radiation levels that
saturate the detector.
⮚Requires calibration and periodic maintenance to ensure
reliability.

11. APPLICATIONS
▪Nuclear Power Plants
Workers are monitored to ensure their exposure stays within safe
limits.
▪Medical Facilities
Used by healthcare professionals working with radioactive
materials.
▪Research Laboratories
Essential for researchers handling radioactive materials.
▪Environmental Monitoring
Used to measure radiation levels in areas potentially affected by
radioactive sources.

12. THERMOLUMINESCENT DOSIMETER
❑A TLD is a passive radiation monitoring
device that measures ionizing radiation
including x ray, gamma and beta
radiation.
❑It was invented by Professor Farrington
Daniels in 1994 .

13. PRINCIPLE
▪TLD works on the principle of thermoluminescence .
▪It works by trapping electrons from ionizing radiation and
releasing them as light when heated.

14. CONSTRUCTION OF TLD
It contains the following:
i. TLD Card consists of three disc each which are
clipped over nickel aluminium card.
i. the discs are made of a thermoluminescent
material nearly tissue equivalent
ii. the discs are 0.8 mm thick and have a 1.35 cm
diameter
ii. Filters against each disc
i. top: aluminium and copper
ii. middle: perspex
iii. lower: open
Card is enclosed by a plastic wrapper

15. THERMOLUMINESCENT MATERIALS
Some of the commonly used materials are
• Lithium fluoride
• Calcium fluoride
• Calcium Sulfate
• Lithium borate
The choice of thermoluminescent material depends on the specific
application , the radiation type and energy range involved.

16. WORKING
▪A TLD typically consists of a small chip of thermoluminescent
material, enclosed in a protective container.
▪When exposed to ionizing radiation, the material absorbs energy
and traps electrons within its crystal lattice.
▪As the material is heated, the trapped electrons are released, and
they recombine with holes, emitting light.
▪ The intensity of the emitted light is proportional to the absorbed
radiation dose.
▪ The process of heating and reading is typically automated in modern
TLDs allowing for efficient and accurate radiation dose
measurements.

17. TLD READER
A typical basic TLD reader contains the
following components:
• Heater - Raises the temperature of the TL
material and light is emitted.
• Photomultiplier tube – Detects the
emitted light and converts it into electrical
signal.
• Amplifier – Amplifies the electrical
signal.
• Meter/Recorder. Recorder is able to
display and record data.
TLD READER

18. ADVANTAGES
• High Sensitivity
• Wide Energy Response
• Dose Accumulation
• Reusability
• Convenient

19. LIMITATIONS
• Require calibration and correction factors for accurate dose
measurements.
• Time-consuming and require specialized equipment.
• Environmental Factors such as humidity and light exposure, can
affect the dosimeter's response and accuracy.

20. SOLID STATE DETECTORS
❑A solid-state detector is a device that uses solid
materials(Semiconductors) to detect and measure ionizing radiation,
such as gamma rays, X-rays, and charged particles.
❑ These detectors operate by converting the energy from incoming
radiation into electrical signals, which can then be processed and
analyzed.
.

21. PRINCIPLE
▪The fundamental principle behind their operation is creation of
electron-hole pairs when radiation interacts with the detector
material.
INCOMING
RADIATION

22. WORKING
1.Radiation Interaction: When an incident photon interacts with the detector
material, it deposits its energy in the semiconductor.
2.Charge Carrier Generation: The energy deposited creates a number of
electron-hole pairs proportional to the incident radiation's energy.
3.Charge Carrier Drift: The generated charge carriers are then driven by an
applied electric field towards opposite electrodes, resulting in a current flow.
4.Signal Amplification: The collected charge carriers are amplified enhancing
the signal strength for better detection and analysis.
5.Signal Processing: The amplified signal is then processed, digitized, and
analyzed to extract information about the incident radiation, such as its energy,
arrival time, and spatial location.

24. TYPES OF SEMICONDUCTOR MATERIALS
• SILICON
• GERMENIUM
• CADMIUM ZINC TELLURIDE AND CADMIUM TELLURIDE

25. ADVANTAGES
• High Sensitivity
• Good Energy Resolution
• Fast Response Time
• Compact Size
• Low Power Consumption
• Versatility

26. LIMITATIONS
• Radiation Damage
• Temperature Dependence
• Limited Radiation Range
• More Expensive
• Noise

27. APPLICATIONS
1.Medical Imaging
 X-ray detectors in radiography PET and SPECT scanners for nuclear medicine imaging.
2.Nuclear and Particle Physics
 Energy measurement of particles using silicon or germanium detectors.
3.Radiation Monitoring
 Personal dosimeters for workers in nuclear facilities.
4.Space Science
 Gamma-ray and X-ray detectors for astronomical observations.
5.Security and Defense
 Baggage scanners at airports (X-ray detectors).
6.Research and Development
 Semiconductor research for studying defects and properties.

28. THANK YOU