1 MEASUREMENT Of γ-RAY ENERGY SPECTRA BY A SCINTILLATION COUNTER Presention group: 1. Zhang Yaxing...
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Transcript of 1 MEASUREMENT Of γ-RAY ENERGY SPECTRA BY A SCINTILLATION COUNTER Presention group: 1. Zhang Yaxing...
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
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Basic configuration and mechanism-ray NaI(Ti)
Scintillator visible light(~eV)
Photomultiplier
Preamp&
Amp
Voltage pulse
Gaussian pulseMulti-channel analyzer
Control &Display
PC
Interaction with matter Detect the light
Amplify and shape the pulseanalog-to-digital conversion
&Count the pulse
Sort the pulses by height
Sodium iodide dynode
Analyse the spectrum
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Photoelectron peakfull energy peak
Compton edge
Compton scattered peak
Three major interactions
2ecm
E)cos1(1
E'E
Photoelectric effect: all the energy is transferred from incident gamma ray to an electron
Compton scattering:
Spectrum Of 137Cs
0.662MeV
Electron-positron pair production : occur only when E > 1.022MeV
photon
electron
' EEEe
' EEEe
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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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Low energy X radiation
Back Scattering Compton scattering
Spectrum of Cs-137
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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
0
400
800
1200
1600
200 300 400 500 600 700
Ch
E(KeV)
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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
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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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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
Result
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Spectrum of unknown source B1
ch #146
304.891 keV
17031 c
ch #175
361.837 keV
38753 c
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Spectrum of unknown source C1
ch #716
1424.17 keV
1649 c
ch #559
1115.88 keV
3248 c
ch #490
980.384 keV
2645 c
ch #395
793.838 keV
3959 c
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Result
Similarly, we get:
B1: Ba133
C1: Eu152
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Graph of energy resolution depends on energy
y = 294.43x-0.5573
55.5
66.5
77.5
88.5
99.510
500 700 900 1100 1300 1500
Energy (keV)
En
erg
y R
eso
luti
on
(%
)
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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
y = 1. 9743x + 3. 7987R2 = 0. 9998
0
200
400
600
800
1000
1200
1400
1600
0 200 400 600 800
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Standard sources
source Eγ/keV A0/kBq (2007.04.1)
1/2T/y λ/s-1 t/dA/kBq
(2009.02.25)
22Na-472 1274.5 6.71 2.62 8.38736E-09 697 4.0491
60Co-12041173.3
72.1 5.26 4.17773E-09 697 56.0625 1332.5
137Cs-2576 661.7 410 30.174 7.28272E-10 697 392.4072
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
I
net
n
N
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
source Eγ/keV Iγ(%) ε Iγ/kBq
54Mn-a1 834.84 100.00% 24.46% 223.83
54Mn-a2 834.84 100.00% 24.46% 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 (E=661.7 KeV)
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Gamma source (137Cs)
Scattering material
Detector NaI
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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
keV288
cm
Ecos11
EE
20
'
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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