Transcript 幻灯片 1 - 大阪大学

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
1
Outline
Basic description
 Calibration
 Identification of unknown sources
 Measurement of efficiency
 Measurement of Compton scattering

2
Basic configuration and mechanism

-ray
visible light(~eV)
Photomultiplier
Interaction with matter
Detect the light
Sodium iodide
dynode
Multi-channel
analyzer
Gaussian pulse
Analyse the spectrum analog-to-digital conversion
&
Count the pulse
Sort the pulses by height
Voltage pulse
Control
&Display
PC
NaI(Ti)
Scintillator
Preamp
&
Amp
Amplify and shape the pulse
3
Three major interactions
Spectrum
Of 137Cs
0.662MeV
Photoelectron peak
full energy peak
Compton
scattered peak

Ee  E  E '
Compton edge
Photoelectric effect: all the energy is transferred from incident gamma ray to an electron
Compton scattering:

photon
electron
E ' 
E
1  (1  cos)
E
mec2
Electron-positron pair production : occur only when E > 1.022MeV
Ee  E  E '
4
Outline
Basic description
 Calibration
 Identification of unknown sources
 Measurement of efficiency
 Measurement of Compton scattering

5
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.
6
How to calibrate energy?
Depending on relation between energy and
channel, we can calibrate energy by measuring
the pulse height spectrum of known sources (Cs137, 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.

7
Spectrum of Cs-137
Low energy X radiation
Back Scattering
Compton scattering
8
Co-60 gamma spectrum
9
Na-22 gamma spectrum
10
Data
Ch
328
586
668
643
E (keV)
661.7
1173.3
1332.5
1274.5
11
Result
E(KeV)
1600
1200
800
400
0
200
300
400
500
600
700
Ch
12
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
13
Outline
Basic description
 Calibration
 Identification of unknown sources
 Measurement of efficiency
 Measurement of Compton scattering

14
Spectrum of unknown source A1
15
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
16
Spectrum of unknown source B1
ch #175
361.837 keV
38753 c
ch #146
304.891 keV
17031 c
17
Spectrum of unknown source C1
ch #395
ch #490
793.838 keV
980.384 keV
3959 c
2645 c
ch #559
1115.88 keV
ch #716
3248 c
1424.17 keV
1649 c
18
Result
Similarly, we get:
B1: Ba133
C1: Eu152
19
Energy Resolution (%)
Graph of energy resolution depends on
energy
10
9.5
9
8.5
8
7.5
7
6.5
6
5.5
5
500
y = 294.43x -0.5573
700
900
1100
1300
1500
Energy (keV)
20
Outline
Basic description
 Calibration
 Identification of unknown sources
 Measurement of efficiency
 Measurement of Compton scattering

21
Energy calibration for MCA
1600
y = 1.9743x + 3.7987
2
R = 0.9998
1400
1200
1000
800
600
400
200
0
0
200
400
600
800
22
Standard sources
source
22
Na-472
Eγ/keV
A0/kBq
(2007.04.1)
λ/s-1
t/d
A/kBq
(2009.02.25)
1274.5
6.71
2.62
8.38736E-09
697
4.0491
72.1
5.26
4.17773E-09
697
56.0625
410
30.174
7.28272E-10
697
392.4072
1/2
T/y
1173.3
60
Co-1204
1332.5
137
Cs-2576
661.7
A=A0exp(-λt)
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Spectrum of the standard sources
1600
137
dem o
1400
dem o
1200
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
800
800
600
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem
60
o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
Co
background
dem o
dem o
GaussFit
of counts
GaussFit of counts
GaussFit
of counts
dem o
dem o
700
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
400
600
200
500
0
0
100
200
300
channel
400
500
600
counts
counts
1000
Cs d e m o
dem o
background
GaussFit
of counts
dem o
dem o
400
300
200
100
0
0
100
200
300
400
500
600
700
800
900
1000
channel
24
Spectrum of the standard sources
counts
300
dem o
dem o
dem o
dem o
dem o
background
22
Na
dem o
dem o
Gaussfit of counts
250
dem o
dem o
dem o
200
dem o
dem o
dem o
dem o
dem o
150
dem o
dem o
dem o
dem o
dem o
100
dem o
dem o
dem o
dem o
dem o
50
dem o
dem o
dem o
dem o
dem o
0
0
100
200
300
400
500
600
700
800
900
1000
channel
!! the source is too weak,
the measurement time is too short.
25
Efficiency of the detector
0.30
effenciency
0.26
0.24
dem o
dem o
dem o
experiment
Polynomial Fit of effenciency
2
dem o
d-4.14285e-4x+0.50958
em o
dem o
y=1.16016e-7x
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
0.28
N
net
 

n
I
N– net count
0.22
n--number of rays from
0.20
the source per seccond
0.18
0.16
0.14
600
700
800
900
1000
1100
1200
1300
1400
energy/keV
26
Spectrum of the unknown sources
2000
1800
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
1600
dem o
background
54
a1( Mn)
dem o
Gaussfit
of counts
1400
1000
500
800
600
dem o
400
dem o
dem o
dem o
dem o
dem o
dem o
dem o
400
dem o
0
0
100
200
300
400
channel
500
600
700
300
800
dem o
background
54
a2( Mn)
dem o
GaussFit of counts
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
200
counts
counts
1200
200
100
0
0
200
400
600
800
channel
27
Spectrum of the unknown sources
40000
dem o
dem o
background
133
b1( Ba)
GaussFit
of counts
dem o
dem o
GaussFit of counts
GaussFit
of counts
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
dem o
counts
30000
20000
10000
0
0
200
400
channel
28
Intensity of the unknown sources
source
Eγ/keV
Iγ(%)
ε
Iγ/kBq
54
Mn-a1
834.84
100.00%
24.46%
223.83
54
Mn-a2
834.84
100.00%
24.46%
34.20
53.16
2.20%
48.79%
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%
133
Ba-b1
576.13
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Outline
Basic description
 Calibration
 Identification of unknown sources
 Measurement of efficiency
 Measurement of Compton scattering

30
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)

31
Detector NaI
Scattering material
Gamma source (137Cs)
32
Spectrum of 137Cs with
scattering material Pb ( = 900)
33
Spectrum of 137Cs without
scattering material (q = 900)
34
Spectrum of 137Cs after comparing 2 above spectra
Compton scattering region
35
RESULT


Compton peak :channel 137
287.2289 keV.
Compared with the result of theoretical formula
E' 
E
E
1  1  cos
m0c 2
 288 keV
36
Spectra with the same scattering
angle (q = 900), different
scattering materials
37
Spectrum of 137Cs with scattering material Fe
38
Spectrum of 137Cs with scattering material Pb
39
Spectrum of 137Cs with scattering material Al
40
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
41
Spectrum with the same scattering
material Al, different scattering angles
42
Spectrum of 137Cs with scattering angle 900
43
Spectrum of 137Cs with scattering angle 750
44
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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