STUDY OF LINEARITY OF GAMMA RAY SPECTROMETER as per the updated details

1. STUDY OF LINEARITY OF
GAMMA RAY SPECTROMETER
Jesna George
DoS in Physics
Manasagangotri

2. CONTENTS
• Scintillation detectors
• Gamma ray spectrometer
• Calibration
• Experiment

3. SCINTILLATION DETECTORS
• Detects the light emitted by a crystal
subjected to ionizing radiation
a) Organic scintillation detector.
b) Inorganic scintillation detector.
• It can be used for counting as well as for
energy analysis.

4. Gamma ray Spectrometer
• Sodium iodide scintillation spectrometer is the
most successful and popular method in
gamma ray spectroscopy.
• Thallium activated sodium iodide crystals are
used as scintillators.
• The scintillation detector is coupled to nuclear
electronic system.

6. Photomultiplier Tubes
• Made up of glass or quartz
• Photocathode
• Dynodes
• Anode

7. Single Channel Analyser
• It is a pulse-height analyser.
• Analysis is made by taking the readings for
one channel at a time.
• There are two discriminators.

8. Gamma spectrum for monoenergetic
gamma ray

9. • The observed spectrum is complex in nature.
• The various absorption processes involved are
a) Photoelectric absorption.
b) Compton effect absorption.
c) Absorption by pair production.

10. • The widening of line into a Gaussian shaped
profile is due to the statistical fluctuations in
the various processes which convert gamma
rays into an output pulse.
• The processes contribute to statistical
fluctuations are

11. • Conversion of incident gamma rays into
luminescence photons
• Light transmission and collection by
photocathode
• Conversion of light into photoelectrons
• Focussing of photoelectrons on dynodes
• Multiplication of electrons

12. Gamma ray detector should
have
• High efficiency of detection.
• Good energy resolution power.
• Linear response to electron.
• Good mechanical and electrical
stability.

13. Characteristics of energy spectrometer
• Linearity :The amplitude of the output
pulse must be directly proportional to
the original number of scintillation and
thus in turn to the energy deposited
• Stability :Gain of each dynode stage
depends on the voltage difference ,any
change in high voltage will cause a
variation in the output pulse.

14. Calibration of gamma ray
spectrometer
• We calibrate the spectrometer to 2 Mev using
the standard source 137
𝐶𝑠.
• The gain is set such that the peak count will
appear on the scale.
• The count is noted for such channel and is
checked for the peak.
• If there is any deviation we repeat the above
steps so that peak is obtained at 33 𝑟𝑑
channel.

15. • The channel around photopeak are set and
counts are noted.
• This is repeated for different sources.
• Resolution for each photopeak is determined.
• A plot of resolution versus energy is made
which should yield a straight line.

16. • Here we have two potentiometers with 10
turns each.
• One acts as ULD and other as LLD.
• ULD : 0 to 1V.
• LLD : 0 to 10V.
• For LLD-1 channel=20 keV

17. AIM
• To study the linearity of gamma ray
spectrometer using SCA and determination of
energy of unknown source.

18. APPARATUS
• Gamma ray spectrometer.
• 137
𝐶𝑠 -source
• 133
𝐵𝑎 -source
• 57
𝐶𝑜 -source
• 60
𝐶𝑜 -source
• 22
𝑁𝑎 -source
• Unknown source.

19. Isotop Energy in keV
137
𝐶𝑠 662
133
𝐵𝑎 365
60
𝐶𝑜 1170
57
𝐶𝑜 122
22
𝑁𝑎 511

20. PROCEDURE
• The energies of various gamma sources are
provided.
• Calibration of gamma ray spectrometer to
2 MeV has been done.
• 137
𝐶𝑠 is treated as the standard source the
counts per 30 second for the entire spectrum
is noted down.
• Photopeak is obtained at channel no.33.

21. • Similarly photopeak for all other known
sources are noted down.
• Then counts per 30 second for the entire
spectrum for the unknown source is recorded.
• For all these sources a graph is plotted
between counts per 30 second and channel
number.
• Thus we obtain the photopeaks.

22. • Now a plot of energy versus peak channel
number is made which will yield a straight
line.
• From this plot we can determine the energy of
the given unknown source.

23. OBSERVATIONS
• 137
𝐶𝑠
Channel
Number
Counts
per 30
secs
Channel
Number
Counts
per 30
secs
Channel
Number
Counts
per 30
secs
Channel
Number
Counts
per 30
secs
3 3106 13 2822 23 1794 33 8318
4 2797 14 2645 24 1008 34 5194
5 2695 15 2429 25 571 35 1627
6 2817 16 2319 26 432 36 135
7 2872 17 2216 27 306 37 16
8 2975 18 2196 28 251 38 20
9 3636 19 2285 29 308 39 8
10 4039 20 2390 30 658 40 14
11 3795 21 2437 31 2438
12 3325 22 2353 32 6115

24. 133
𝐵𝑎
Channel number Counts per 30 secs Channel number Counts per 30 secs
9 4477 17 8884
10 3249 18 11705
11 2031 19 6152
12 1671 20 2364
13 2539 21 749
14 4543 22 507
15 5745 23 391
16 4262

25. • 60
𝐶𝑜
Channel
number
Counts per 30
secs
Ch51annel
numb42er
Counts per 30
secs
50 3141 59 50
51 2366 60 42
52 779 61 36
53 1333 62 37
54 2503 63 33
55 1319 64 25
56 251 65 21
57 55 66 26
58 42

26. • 57
𝐶𝑜
Channel
number
Counts per 30
secs
Channel
number
Counts per 30
secs
1 22 6 140
2 28 7 47
3 59 8 25
4 67 9 21
5 78 10 14

27. • 22
𝑁𝑎
Channel
number
Counts
per 30
secs
Channel
number
Counts
per 30
secs
Channel
number
Counts
per 30
secs
Channel
number
Counts
per 30
secs
22 100 33 42 44 95 55 12
23 153 34 54 45 109 56 7
24 550 35 51 46 97 57 7
25 1163 36 66 47 82 58 6
26 1263 37 71 48 41 59 5
27 497 38 72 49 35 60 5
28 122 39 78 50 90 61 1
29 67 40 81 51 53 62 0
30 44 41 88 52 150
31 51 42 82 53 201
32 62 43 87 54 62

28. • Unknown source
Chann
el no.
Count
s/30se
cs
Chann
el no.
Count
s/30
secs
Chann
el no.
Count
s/30
secs
Chann
el no.
Count
s/30
secs
Chann
el no.
Count
s/30
secs
1 1652 14 568 27 801 40 113 53 260
2 545 15 521 28 161 41 109 54 78
3 667 16 485 29 61 42 128 55 11
4 570 17 300 30 51 43 111 56 4
5 593 18 229 31 71 44 129 57 9
6 663 19 145 32 67 45 157 58 5
7 649 20 118 33 79 46 132 59 1
8 684 21 129 34 82 47 87 60 0
9 843 22 138 35 69 48 53 61 4
10 852 23 228 36 79 49 27 62 2
11 759 24 701 37 77 50 22 63 0
12 685 25 1609 38 86 51 64 64 0
13 581 26 1662 39 103 52 211

29. 𝟏𝟑𝟕
𝑪𝒔 𝟏𝟑𝟑
𝑩𝒂
-1000
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 10 20 30 40 50 0
2000
4000
6000
8000
10000
12000
14000
0 5 10 15 20 25

30. 𝟔𝟎
𝑪𝒐 𝟓𝟕
𝑪𝒐
0
500
1000
1500
2000
2500
3000
3500
40 50 60 70 80
0
20
40
60
80
100
120
140
160
0 2 4 6 8 10 12

31. 𝟐𝟐
𝑵𝒂 Unknown source
0
200
400
600
800
1000
1200
1400
0 10 20 30 40 50 60 70 -200
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 10 20 30 40 50 60 70

32. Source Energy Peak channel
137
𝐶𝑠 662 33
133
𝐵𝑎 356 18
60
𝐶𝑜 1170 54
1330 59
57
𝐶𝑜 122 6
22
𝑁𝑎 511 26
Unknown source 510 26

34. RESULT
• The plot yield a straight line which shows the
linearity of the spectrometer.
• The energy of the unknown source is 510 keV.

35. REFERENCES
• Singru R.M.,Experimental Nuclear
Physics,Wiley Eastern Pvt Ltd,Delhi,1972.
• Kapoor S.S.;Ramamurthy V.S,Nuclear
Radiation Detectors,New Age International
Publishers,Delhi,2008.
• Ghoshal S.N.,Nuclear Physics,S.Chand and
Company,Delhi,1994.

36. THANK YOU