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 Measurement of Compton scattering

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

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

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

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.

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.

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

Co-60 gamma spectrum

Na-22 gamma spectrum

Data Ch E (keV) 328 661.7 586 1173.3 668 1332.5 643 1274.5

Result

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

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

Spectrum of unknown source A1

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

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

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

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

Graph of energy resolution depends on energy

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

Energy calibration for MCA

Standard sources A=A0exp(-λt) source Eγ/keV A0/kBq (2007.04.1) 1/2T/y t/d A/kBq (2009.02.25) 22Na-472 1274.5 6.71 2.62 8.38736E-09 697 4.0491 60Co-1204 1173.3 72.1 5.26 4.17773E-09 56.0625 1332.5 137Cs-2576 661.7 410 30.174 7.28272E-10 392.4072 A=A0exp(-λt)

Spectrum of the standard sources

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

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

Spectrum of the unknown sources

Spectrum of the unknown sources

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%

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

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)

Detector NaI Scattering material Gamma source (137Cs)

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

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

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

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

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

Spectrum of 137Cs with scattering material Fe

Spectrum of 137Cs with scattering material Pb

Spectrum of 137Cs with scattering material Al

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

Spectrum with the same scattering material Al, different scattering angles

Spectrum of 137Cs with scattering angle 900

Spectrum of 137Cs with scattering angle 750

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

Thank you very much for your attention