Experiment 2 Introduction Results Part 1 – Conduct a 3-point energy calibration

Experiment 2

Introduction

Results

Part 1 – Conduct a 3-point energy calibration of the detector

Gamma Emitter

Channel Number

Expected Gamma ray energies

Am-241

26

59.5

Na-22

76

511

188

1274.5

Part 2 – Identification of an unknown source

Channel number

Measured Energy (Kev)

Expected Energy (Kev)

Identified isotopes

99

662

661.6

Cs137

The source was identified as Cs 137, as per the founded measurement Cs 137 was spouse to have 2 peaks for the isotope but only one peak was recorded because of the low probability of

The below calculation shows the measured energy in keV

Part 3: Identify components of a gamma spectrum of a 22Na source

Spectrum Feature

Measured energy (Kev)

Theoretical energy (Kev)

X-ray peak(s)

Not observed

0.849

Backscatter peak

187.9

212.8

Positron annihilation

513.1

511

Single escape Peak

Not observed

252

Double escape peak

277.2

763

Compton edge(s)

1019

1061.2

Photo peak(s)

1272.2

1274.5

Sum Peak (s)

1762

1785.5

Theoretical components were calculated as per the below equations.

E

E

C

C

F

F

G

G

H

H

B

B

Part-4: find the energy resolution characteristics of the detector

Source

Measured Energy (Kev)

FWHM (Kev)

Energy Resolution %

Na-22

513.1

84

16.37%

Na-22

1272.2

70

5.50%

Mn-54

830

54

6.51%

Co60

1160.6

39

3.36%

Co60

1314.2

43

3.27%

Cd-109

98.4

57

57.93%

Cs-137

660.2

94

14.24%

Figure 10: illustrates the Measured energy resolution of LaBr3:Ce, LaCl3:Ce, NaI(Tl) and HPGe detectors – ENTER REFRENCE

Part-5: Efficiency calibration using pre-recorded data

Source

Measured Energy (kev)

Documented Energy (kev)

NPA Counts

Counting Duration (s)

Count Rate (s-1)

Na-22

514

511

59359

62

957.40

Na-22

1268.3

1274.5

7858

62

126.74

Mn-54

826

834.8

2767

60

46.12

Co-60

1161.1

1173

4511

61

73.95

Co-60

1300.2

1332.5

2431

61

39.85

Cd-109

97.5

88

2862

60

47.70

Cs-137

657.9

661.7

3023

60

50.38

COUNT RATE = net peak area counts / Duration

Isotope

Half life (Y/D)

Half life (s)

Decay constant (1/s) =ln2/Half life

Days from certification 1 May 2020 till 3 nov 2022

Elapsed time from certification (s)

Decay Correction (e^-λt)

Original activity (Bq) = # μ CI

Decay corrected activity (Bq)

Na-22 (Y)

2.6

8.2E+07

8.5E-09

915

7.9E+07

0.513

3.7E+04

1.9E+04

Mn-54 (D)

313

2.7E+07

2.6E-08

915

7.9E+07

0.132

3.7E+04

4.9E+03

Co-60 (Y)

5.26

1.7E+08

4.2E-09

915

7.9E+07

0.719

3.7E+04

2.7E+04

Cd-109(D)

462.6

4.0E+07

1.7E-08

915

7.9E+07

0.254

3.7E+04

9.4E+03

Cs-137 (Y)

30.07

9.5E+08

7.3E-10

915

7.9E+07

0.944

1.9E+04

1.7E+04

The decay corrected activity of 22Na is calculated below:

Isotope

Energy (kev)

Yield (%)

Count rate (1/s)

Decay corrected activity (Bq)

Absolute efficiency

Na-22

514

180

957.4

18965

0.028

Na-22

1268.1

99.94

126.7

18965

0.007

Mn-54

826

99.98

46.1

4877

0.009

Co-60

1161.1

99.97

74

26591

0.003

Co-60

1300.2

99.99

39.9

26591

0.001

Cd-109

97.5

3.61

47.7

9392

0.141

Cs-137

657.9

85.12

50.4

17461

0.003

The Absolute efficiency of 109Cd is calculated below:

Discussion:

Part 1 – Conduct a 3-point energy calibration of the detector

Q8. If the source is emitting gamma-rays at fixed energies, then why does the spectrum show count in other channels? Explain.

The spectrum can show counts in other channels due to the scattering phenomena.

Q9. Can you perform energy calibration with just one Cs-137 as a provided sample, given that this source emits a gamma-ray at 661.6 keV?

Yes, it is theoretically possible. However, it is best to use more than one known source to be able to find the best fit for the unknown data points.

Q10. Is the above calibration that you performed sufficient to accurately measure a sample which gives gamma-rays with energy ~185 keV? Explain your answer.

Yes, the above calibration is sufficient as the gamma rays of energy 185keV lied within the calibration energy range.

Part 2 – Identification of an unknown source

Q6. Specify two reasons for the difference between measured and expected energies.

Instrumental or systemic error from the detector and scattering and absorption of gamma rays.

Q7. How will you distinguish two isotopes with gamma-ray energies very close to each other, for example, one at 184.6 keV and another at 186.1 keV?

To distinguish energies that are very close as the ones mentioned in the question, it is best to use a high-resolution detector.

Part-3: Identify components of a gamma spectrum of a 22Na source

Q1. Calculate the mass of an electron using the measured value of Compton edge energy and annihilation peak energy. Report the difference of calculated values from best known value of electron mass.

Compton Edge =

Therefore, =

Difference of calculated values from best known value of electron mass = =

Part-4: find the energy resolution characteristics of the detector

Q?? Report the measured FWHM for 137Cs @ 661 keV. Compare it with the theoretically expected value for NaI detectors of around 6—8%.

The measured resolution of 137Cs was 14%. This indicates that the detector used has a lower resolution.

Part-5: Efficiency calibration using pre-recorded data

Q?? Explain the behavior of the efficiency curve in low energy and high energy regions.

From the obtained results, the efficiency curve is decreasing with energy increasing, in the high energy region. However, for the Americium the detector did not detect the low energy measurement.

Q?? Can this calibration suffice for the proposed measurement in part-1 step 10?

Yes, the calibration will suffice for a peak in the 185 kev region.

Conclusion

References