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
