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

12. Result

13. Equation of energy calibration
From the least squares method, we get
a = 
b = 
Thus,
E = *Ch

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 =  15.2 (keV)
A1: Mn56

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

18. 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

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) 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)

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
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%

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