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Efficiency Calibration Curve
Make an efficiency calibration curve, where the counting efficiency is given as a function of
γ energy. In table 1 the measured nuclei is listed with
γ energy, number of counts, uncertainty in the number of counts and the counting time. The measurements was performed 27th March 2003.
table 1 : measurement data from standard γ-calibartion sources, measured 6. oct 2006.
|
Nuclide
|
Energy (keV)
|
Counts
|
Uncertainty
|
Real Time (s)
|
137Cs
|
661.66
|
161681
|
432
|
210
|
|
|
|
|
|
133Ba
|
80.997
|
99426
|
408
|
380
|
|
276.398
|
13284
|
150
|
380
|
|
302.853
|
31734
|
202
|
380
|
|
356.017
|
92291
|
322
|
380
|
|
|
|
|
|
241Am
|
59.54
|
407142
|
766
|
376
|
|
|
|
|
|
60Co
|
1173.237
|
14039
|
137
|
189
|
|
1332.501
|
12822
|
121
|
189
|
|
|
|
|
|
54Mn
|
834.84
|
317
|
26
|
1268.56
|
|
|
|
|
|
152Eu
|
121.78
|
486526
|
1031
|
1111
|
|
244.698
|
82174
|
519
|
1111
|
|
344.279
|
211766
|
625
|
1111
|
|
778.9
|
48601
|
396
|
1111
|
|
295.939
|
4076
|
245
|
1111
|
|
964.079
|
45298
|
359
|
1111
|
|
1408.006
|
47191
|
237
|
1111
|
A table of the
γ intensities, I
γ, can be found
Gamma-Energy Standards
To calculate the efficiency you need to know the amount of activity in the sources. Table 2 lists the amount of activity at the time of purchase. You must correct these number based upon the age and half life of the sources.
table 2: activety of standards
|
Nuclide:
|
activety:
|
Date
|
60Co
|
10.57 μCi
|
1. oct 1988
|
133Ba
|
6.09 μCi
|
1. oct 1988
|
54Mn
|
367 kBq
|
1. apr 1996
|
137Cs
|
11.5 μCi
|
1. oct 1988
|
241An
|
11.56 μCi
|
1. oct 1988
|
152Eu
|
3.71 μCi
|
1.apr 2004
|
Determination of Unknown Sample
In table 3 the analysis results of the unknown, n-irradiated sample is shown. Use the results to :
- Determine which metal the sample consist of. Use the identified γ-ray energies to do this. if you need a database you can use this one
- Determine the absolute amount of the metal. Use the counts measured in table 3 and the efficiency curve you made in exercise 3B. Use at least two different γ lines to do this, we recommend Eγ = 222.08 keV and Eγ 1 MeV. The neutron flux was 105 n/(s cm2) during the irradiation, and the irradiation time was 18 days. The sample was measured directly after the irradiation.
Table 3: Results from spectroscopy of unknown sample
|
Photo Peak no.
|
Energy (keV
|
Net Count
|
Uncertainty
|
FWHM (keV
|
1
|
67.63
|
166011
|
1885
|
0.44
|
2
|
100.26
|
79985
|
902
|
1.00
|
3
|
152.56
|
34987
|
401
|
1.16
|
4
|
222.08
|
29011
|
335
|
1.52
|
5
|
511
|
210890
|
2385
|
2.24
|
6
|
1121.14
|
32098
|
391
|
1.67
|
7
|
1188.7
|
14563
|
173
|
1.17
|
8
|
1221.28
|
23825
|
265
|
2.01
|