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Solid state detector mamita

Detectors in use

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Solid state detector mamita

  1. 1. SOLID STATE DETECTOR 1 MAMITA SAKHAKARMI B.Sc.MIT 4th BATCH 1ST YEAR Chitwan Medical College
  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
  6. 6. INORGANIC SCINTILLATORS 6
  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
  8. 8. ORGANIC SCINTILLATORS COME IN MANY FORMS 8
  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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