Dosimeter used in Radio Imaging Technology
- 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.
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