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MEASUREMENT Of γ-RAY ENERGY SPECTRA BY A SCINTILLATION COUNTER

MEASUREMENT Of γ-RAY ENERGY SPECTRA BY A SCINTILLATION COUNTER. Presention group: 1. Zhang Yaxing 2. Van Thi Thu Trang 3. Doan Thi Hien 4. Li Chunjuan 5. Nguyen Duy Thong. Outline. Basic description Calibration Identification of unknown sources Measurement of efficiency

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MEASUREMENT Of γ-RAY ENERGY SPECTRA BY A SCINTILLATION COUNTER

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  1. MEASUREMENT Of γ-RAY ENERGY SPECTRA BY A SCINTILLATION COUNTER Presention group: 1. Zhang Yaxing 2. Van Thi Thu Trang 3. Doan Thi Hien 4. Li Chunjuan 5. Nguyen Duy Thong

  2. Outline • Basic description • Calibration • Identification of unknown sources • Measurement of efficiency • Measurement of Compton scattering

  3. Basic configuration and mechanism NaI(Ti) Scintillator visible light(~eV) -ray Photomultiplier Voltage pulse Interaction with matter Detect the light Sodium iodide dynode Control &Display PC Preamp & Amp Multi-channel analyzer Gaussian pulse Analyse the spectrum analog-to-digital conversion & Count the pulse Sort the pulses by height Amplify and shape the pulse

  4. Three major interactions Spectrum Of 137Cs 0.662MeV Photoelectron peak full energy peak Compton scattered peak Compton edge Photoelectric effect: all the energy is transferred from incident gamma ray to an electron Compton scattering: photon electron Electron-positron pair production : occur only when E > 1.022MeV

  5. Outline • Basic description • Calibration • Identification of unknown sources • Measurement of efficiency • Measurement of Compton scattering

  6. Energy-calibrated scintillation counter Why have to calibrate energy? Gamma Peak energies taken from APTEC MCA program may be not correct. We have to calibrate before using this program.

  7. How to calibrate energy? • Depending on relation between energy and channel, we can calibrate energy by measuring the pulse height spectrum of known sources (Cs-137, Co-60, Na-22). • The calibration line is linear of the form E = a*Ch + b Where: E is the energy of gamma. Ch is channel related to Energy. Using the least squares method to determine a and b factors.

  8. Spectrum of Cs-137 Low energy X radiation Back Scattering Compton scattering

  9. Co-60 gamma spectrum

  10. Na-22 gamma spectrum

  11. Data

  12. Result

  13. Equation of energy calibration From the least squares method, we get a = 0.9637  0.0213 b = 18.2019  12.2074 Thus, E = 1.9637*Ch + 18.2019

  14. Outline • Basic description • Calibration • Identification of unknown sources • Measurement of efficiency • Measurement of Compton scattering

  15. Spectrum of unknown source A1

  16. Result Calibrated energy line: E(keV) =1.9637Ch+18.2019 From the above spectrum, we get Ch = 424  E = 850.8  15.2 (keV) A1: Mn56

  17. Spectrum of unknown source B1 ch #175 361.837 keV 38753 c ch #146 304.891 keV 17031 c

  18. Spectrum of unknown source C1 ch #490 980.384 keV 2645 c ch #395 793.838 keV 3959 c ch #559 1115.88 keV 3248 c ch #716 1424.17 keV 1649 c

  19. Result Similarly, we get: B1: Ba133 C1: Eu152

  20. Graph of energy resolution depends on energy

  21. Outline • Basic description • Calibration • Identification of unknown sources • Measurement of efficiency • Measurement of Compton scattering

  22. Energy calibration for MCA

  23. Standard sources A=A0exp(-λt)

  24. Spectrum of the standard sources

  25. Spectrum of the standard sources !! the source is too weak, the measurement time is too short.

  26. Efficiency of the detector N– net count n--number of rays from the source per seccond

  27. Spectrum of the unknown sources

  28. Spectrum of the unknown sources

  29. Intensity of the unknown sources

  30. Outline • Basic description • Calibration • Identification of unknown sources • Measurement of efficiency • Measurement of Compton scattering

  31. Setup of the experiment • HV: 800 V. • Time: 600 s. • Scattering Material : Pb, Fe, Al. • Scattering Angle: 900 , 750. • Gamma Source 137Cs (Eg=661.7 KeV)

  32. Detector NaI Scattering material Gamma source (137Cs)

  33. Spectrum of 137Cs with scattering material Pb ( = 900)

  34. Spectrum of 137Cs without scattering material (q = 900)

  35. Spectrum of 137Cs after comparing 2 above spectra Compton scattering region

  36. RESULT • Compton peak :channel 137 287.2289 keV. • Compared with the result of theoretical formula

  37. Spectra with the same scattering angle (q = 900), different scattering materials

  38. Spectrum of 137Cs with scattering material Fe

  39. Spectrum of 137Cs with scattering material Pb

  40. Spectrum of 137Cs with scattering material Al

  41. Compare the Compton scattering peak channel of 3 above spectra • Theory: Ch = 137 • Spectrum: • Scattering material Fe: Ch = 138 • Scattering material Pb: Ch = 137 • Scattering material Al: Ch = 132

  42. Spectrum with the same scattering material Al, different scattering angles

  43. Spectrum of 137Cs with scattering angle 900

  44. Spectrum of 137Cs with scattering angle 750

  45. Compare the Compton scattering peak channel of 2 above spectra • Scattering Angle 900: • Spectrum: Ch = 132 • Theory: Ch = 137 • Scattering Angle 750: • Spectrum: Ch = 159 • Theory: Ch = 163

  46. Thank you very much for your attention

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