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Solid state detector mamita

Detectors in use

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Solid state detector mamita

  2. 2. DETECTORS An instrument responsible for detection of ionizing radiations by interacting with matter or to measure radiation or to do both. Types  Gas filled detector  Solid state detector 2 •
  3. 3. SOLID STATE DETECTOR This consists of the solid materials with fluorescence, phosphorescence and semiconducting properties. Types  Scintillation Detector  Thermo luminescent dosimeter  Semiconductor Detector 3
  4. 4. Scintillation detectors:  Detectors based on scintillation (light emission) Working Principle 4
  5. 5. Types  Inorganic crystals  Organic crystals  Inorganic crystals  Generally, high atomic number and high density materials  NaI, CsI, Lithium glasses, ZnS  Commonly used for gamma-ray detection  High light yield (60,000/ Mev)  Can’t be used in liquid form.  Low decay time about 1 microsecond 5
  7. 7. Organic crystals  low atomic numbers, relatively low density.  Low light yield (1000photons/ Mev)-power signal  Can be used in both liquid and solid form.  Economic  Fast decay time about 10 nanosecond  Commonly used for Beta particles detection E.g. trans-stilbene, Anthracene, Naphthalene etc. Generally, in our department inorganic crystals are used because of their high at. no. n high densities that make them good x-ray n gamma ray detector. 7
  9. 9. THERMO LUMINESCENT DOSIMETER 9 • TLD is excellent personnel and environmental dosimeter. • It is based on Thermoluminescence.
  10. 10. Measurement of Thermoluminescence 10
  11. 11.  “Captures” radiation dose information in a crystal matrix.  Releases light when heated, light intensity proportional to radiation dose absorbed.  Information destroyed when processed.  Should be annealed before reused.  1 1
  12. 12. TYPES OF TLD MATERIAL Commonly used LiF:Mg,Ti, LiF:Mg,Cu,P and Li2B4O7:Mn, because of their tissue equivalence. Most widely used is LiF.  Atomic no. is 8.2 that is nearly tissue equivalent (7.4 for soft tissue)  LiF is relatively sensitive and can measure as low as 5 mRad with modest accuracy.  CaF2 has higher effective atomic no. (z= 16.3)  TLDs are available in various forms (e.g. powder, chips, rods and ribbons).  Can be expensive (reusable chips) 12
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  15. 15. Glow curve : graph obtained by plotting phosphor temperature (ºC) against intensity of emitted light. 15 Phosphor temperature (C) EmittedLightIntensity
  16. 16. Practical consideration :  Must be calibrated before use.  Since the response of the TLD material is affected by their previous radiation history and thermal history, the material must be annealed to removed residual effect.  Should be worn at chest position.  Changed in every 3 months.  Should be stored away from light, radiation and dust when it is not used.  Should not be used beside concern personnel. 16
  17. 17. SEMICONDUCTOR DETECTOR  Detector of choice of very high resolution energy measurement  Response that varies linearly with the energy deposited in the detector and doesn't depend upon the type of radiation that deposits the energy  Negligible absorption of energy  Small detector size 17
  18. 18. 18  Act as a solid state ionization chamber.  Operation depends on having either an excess of electrons or an excess of holes
  19. 19. Semiconductor Detectors 19
  20. 20. 20  Common materials of choice Silicon and Geranium  Generally, used for the detection of alpha and beta particles.  Light radiation can be detected in semiconductors through release of charges across the band gap  Higher energy radiation can be expected to do so at much higher efficiencies.  A metal-oxide semiconductor field effect transistor (MOSFET) is a miniature silicon transistor.  Use as vivo dosimeter in rectum and urinary bladder
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