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Published byRoland Williams Modified over 9 years ago
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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
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Outline Basic description Calibration
Identification of unknown sources Measurement of efficiency Measurement of Compton scattering
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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
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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
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Outline Basic description Calibration
Identification of unknown sources Measurement of efficiency Measurement of Compton scattering
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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.
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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.
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Spectrum of Cs-137 Low energy X radiation Back Scattering
Compton scattering
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Co-60 gamma spectrum
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Na-22 gamma spectrum
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Data Ch E (keV) 328 661.7 586 1173.3 668 1332.5 643 1274.5
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Result
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Equation of energy calibration
From the least squares method, we get a = b = Thus, E = *Ch
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Outline Basic description Calibration
Identification of unknown sources Measurement of efficiency Measurement of Compton scattering
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Spectrum of unknown source A1
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Result Calibrated energy line: E(keV) =1.9637Ch+18.2019
From the above spectrum, we get Ch = 424 E = 15.2 (keV) A1: Mn56
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Spectrum of unknown source B1
ch #175 keV 38753 c ch #146 keV 17031 c
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Spectrum of unknown source C1
ch #395 keV 3959 c ch #490 keV 2645 c ch #559 keV 3248 c ch #716 keV 1649 c
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Result Similarly, we get: B1: Ba133 C1: Eu152
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Graph of energy resolution depends on energy
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Outline Basic description Calibration
Identification of unknown sources Measurement of efficiency Measurement of Compton scattering
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Energy calibration for MCA
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Standard sources A=A0exp(-λt) source Eγ/keV A0/kBq (2007.04.1) 1/2T/y
t/d A/kBq ( ) 22Na-472 1274.5 6.71 2.62 E-09 697 4.0491 60Co-1204 1173.3 72.1 5.26 E-09 1332.5 137Cs-2576 661.7 410 30.174 E-10 A=A0exp(-λt)
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Spectrum of the standard sources
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Spectrum of the standard sources
!! the source is too weak, the measurement time is too short.
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Efficiency of the detector
N– net count n--number of rays from the source per seccond
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Spectrum of the unknown sources
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Spectrum of the unknown sources
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Intensity of the unknown sources
Eγ/keV Iγ(%) ε Iγ/kBq 54Mn-a1 834.84 100.00% 24.46% 223.83 54Mn-a2 34.20 133Ba-b1 53.16 2.20% 48.79% 576.13 79.61 2.62% 47.73% 81.00 34.11% 47.68% 160.61 0.65% 44.60% 223.24 0.45% 42.29% 276.40 7.15% 40.39% 302.85 18.30% 39.48% 356.01 61.94% 37.68% 383.85 8.91% 36.77%
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Outline Basic description Calibration
Identification of unknown sources Measurement of efficiency Measurement of Compton scattering
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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)
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Detector NaI Scattering material Gamma source (137Cs)
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Spectrum of 137Cs with scattering material Pb ( = 900)
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Spectrum of 137Cs without scattering material (q = 900)
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Spectrum of 137Cs after comparing 2 above spectra
Compton scattering region
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RESULT Compton peak :channel 137 287.2289 keV.
Compared with the result of theoretical formula
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Spectra with the same scattering angle (q = 900), different scattering materials
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Spectrum of 137Cs with scattering material Fe
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Spectrum of 137Cs with scattering material Pb
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Spectrum of 137Cs with scattering material Al
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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
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Spectrum with the same scattering material Al, different scattering angles
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Spectrum of 137Cs with scattering angle 900
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Spectrum of 137Cs with scattering angle 750
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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
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Thank you very much for your attention
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