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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-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