, (ii) cs ba na
TRANSCRIPT
Experiment – 4
(This should be carried out only by RADLab software)
Objective: Analysis of -ray energy spectra with Multi-Channel Analyzer (MCA).
Sources: -ray source = (i) Co60
, (ii) Cs137
, (iii) Ba133
, and (iv) Na22
Detectors: (i) NaI(Tl) 2x2, (ii) NaI(Tl) 3x3, (iii) NaI(Tl) 5x5, (iv) NaI(Tl) 7x7, (v) NaI(Tl) 2x2
Well-Type, (vi) CdZnTe, (vii) BgO, (viii) HpGe.
Scope of the Expt:
This experiment has two major parts:
Part-A: (i) To Calibrate the MCA by a known radio-active source i.e Co60
with a NaI(Tl) 2x2
detector. (ii) To Find out the -ray energies of unknown sources like (a) Cs137
, (b) Ba133
, and (c)
Na22
using the same NaI(Tl)2x2 detector.
Part-B: (i) Finding detector resolution and (ii) photo-peak efficiency of different type of
detectors [ (a) NaI(Tl) 2x2, (b) NaI(Tl) 3x3, (c) NaI(Tl) 5x5, (d) NaI(Tl) 7x7, (e) NaI(Tl) 2x2
Well-Type, (f) CdZnTe, (g) BgO, (h) HpGe ] at 1.173 Mev and 1.332 Mev using Co60
radio-
active source.
Theory : Write necessary theory for -ray interaction with matter. Decay of -ray sources like
Co60
, Cs137
, Ba133
, and Na22
. Write about scintillation detector, photo-multiplier tube etc.. Here
is a table describing source energy with % of intensity.
Table - Source Energy with % of Intensity
Sl.
No
Nuclide Symbol Half Life Intensity Energy (MeV)
1. Sodium Na22
2.6 Years
100 % 1.275
e- e+
Annihilation 0.511
2. Cobalt Co60
5.27 Years 100 % 1.173
100 % 1.332
3. Cesium Cs137
30 Years 100 % 0.662
4. Barium Ba133
10.66 Years
8 % 0.382
34 % 0.08
69 % 0.356
14 % 0.302
7 % 0.276
How to setup experiment in RADLab :
Go to the folder called "RADlab" under "Program Files"
Right click on "run.bat" and "Run as Administrator". REDLab will start and it will show User Login icon.
Give User Login Creditential : Use “New User” to create your own ID and Password. Or use the following dafult ID and Password. User Name: demo Password: demo
Now, you can construct your Expt-4. You need the following items.
1) -ray Sources
Co-60
Cs-137
Ba-133
Na-22
2) -ray detectors
NaI(Tl) 2x2
NaI(Tl) 3x3
NaI(Tl) 5x5
NaI(Tl) 7x7
NaI(Tl) 2x2 Well-Type
CdZnTe
BgO
HpGe 3) High Voltage source (0 – 3000 V) 4) Pre-amplifier 5) Amplifier 6) Multi Channel Analyzer (SCA) Now go to Administration, then click on “Create Experiment”
Now, Select Experiment Type :
o Gamma Experiment Now
Now, Select Source Type :
o Co-60 o Cs-137 o Ba-133 o Na-22
You can select / choose multiple source just by pressing ctrl +
source Now All sources are designed with Monte Carlo Simulation. Monte
Carlo Simulation is a mathematical technique that generates
random variables for modeling uncertainty of a certain system.
The random variables or inputs are modeled on the basis of
probability distributions such as normal distribution to be
followed in a typical radioactive source.
Now, Select Detectors :
o NaI(Tl) 2x2 o NaI(Tl) 3x3 o NaI(Tl) 5x5 o NaI(Tl) 7x7 o NaI(Tl) 2x2 Well-Type o CdZnTe o BgO o HpGe
You can select / choose multiple detector just by pressing ctrl +
detector type. Now How does a NaI(Tl) work ? To know more read supplied
literatures or from reference books or from internet sources.
You can also read about all detectors, modules etc. from Help of RADLab as shown below. It has a nice description about all instruments. Otherwise follow reference Books.
> Next
> Next
> Next
Radiation Detection and Measurement; By G. F. Knoll
Nuclear Radiation Detection, Measurements and Analysis; By K. M. Varier
Nuclear Radiation Detectors; By S. S. Kapoor and V. S. Ramamurthy
Now, Select required NIM Modules :
o Amplifier o PreAmplifier o HV Supplier o MCA
Now You can select / choose multiple NIM module just by
pressing ctrl + NIM Module
You can give Experiment Name : Expt 4 Also choose Experiment Sheet as text : Expt 4 A documentation file in .html is not available
currently for Expt 4 and in future we shall make it. In
that case you can upload / choose the other option i.e
Experiment Sheet (as html).
Now, verify your selection i.e Detector, Source, NIM Modules etc. Now
Now go to File --> Select Experiment --> Expt 3 Now After that click on You can transfer all of them to your work bench just by clicking on “Co-60” then clicking on “work bench”. Transfer required instruments to your work bench.
> Next
Finish
Select
Instrument
After that click on You can connect the cables to your modules available in “work bench”. Use the appropriate cables as mentioned below
Red Cable : HV Signal Cable
Gray Cable : Signal Cable
Violate Cable : PreAmp Power Cable
Now you have all your required Source, Detector, NIM Modules, and Cables in your work bench. Now connect the cables as described below. Carry out the experiment with the designed parameters. You can click on to start the experiment (use the parameters).
A) Part-A Experiment
Set Parameters:
i) HV Supply: Set the appropriate voltage (0.90 kV) to NaI(Tl)2x2 detector.
ii) Amplifier Gain: Set Course Gain = 50 and Fine Gain = 50.
iii) Source –Detector distance: x = 3.048..cm , y = 0.00 cm
Cables
Run
iv) MCA Setting:
Click this icon to show the MCA output in a different frame.
Click on “Edit” and select “Start and Stop via main control”.
Click this icon to clear data.
Click on “Edit” then “Setup” and select “Real Time” and put 600 and set. This will set 600 sec as
counting time and after the completion the MCA will stop automatically.
Now start experiment by clicking RUN in main panel.
A. Calibration and Determination of Cs137
peak
You have already chosen Co60
which has two photo peak in order to perform this calibration. The
first and second photo peaks of Co60
comes at certain channels which corresponded to the
energies of 1.173 MeV and 1.332 MeV respectively. Find the channel numbers of the peaks by
fitting a Gaussian profile to the peak and get the centroid of the peaks. Then calibrate by using
the following formula. The Energy of any unknown peak can be found by:
where EA is the energy (1.173 MeV) of the first point used for calibration at channel no. A. EB is
the energy (1.332 MeV) of the second point used for calibration at channel no. B.
Use the same calibration to find the unknown energy peak(s) of Cs137
, Ba133
, and Na22
.
Energy = Energy of unknown peak of Cs137
, Ba133
, or Na22
,
Channel number = Channel number of unknown peak of Cs137
, Ba133
, or Na22
The Co60
spectrum
The following two reference points from the spectrum of Co60
are used for calibration. Fit the
individual peak of the spectra by a Gaussian fit to get the centroid as channel number.
1st peak centroid = Ch. No. 1435.26 = 1.173 MeV
2nd
peak centroid = Ch. No. 1636.34 = 1.332 MeV
The Cs137
spectrum
Now clear the data from MCA and replace the Co60
source by the Cs137
source to find out its
energies.
Fit the peak of the spectra by a Gaussian fit to get the centroid as channel number. Then use the
above calibration to find the energy of Cs137
peak.
Now in the similar way find out the unknown energies of Ba133
and Na22
radio active sources.
Always use the same calibration with respect to Co60
energies. Compare the energies with the
supplied standard values (see Table, theory section).
B1. Photo peak efficiency
Photo-peak efficiency is defined as the ratio of the area under the peak to that of the area of the
whole spectrum.
Area 1.17 MeV peak 1.33 MeV peak the whole spectrum
Counts 66080 62156 901383
Efficiency 0.0733 0.0690 -
B2. Determination of resolution of different detectors at 1.173 Mev and 1.332 Mev.
Now use Co60
as source and take different detectors. Use the following HV supply, amplifier
gain, and measure for t = 600 sec in the MCA. Find out the photo peak efficiency as mentioned
above. Keep source-detector distance as 3.048 cm always. Do peak fitting and find out the
FWHM of the two peaks of Co60. The resolution of the detector at energy, E is defined as
You can find after peak fitting the following for each detector to determine the energy resolution:
E1, ΔE1 and R1 are for the first Cobalt peak (1.172 Mev).
E2, ΔE2 and R2 are for the second Cobalt peak (1.332 Mev).
Sl.
No
Detector
Type
HV (kV)
Supply
Amp. Gain Photo peak efficiency Energy Resolution @ Course Fine 1.173 Mev 1.332 Mev 1.173 Mev 1.332 Mev
1 NaI(Tl)
2x2
0.90 70 0
2 NaI(Tl)
3x3 1.20 50 50
3 NaI(Tl)
5x5 1.50 50 50
4 NaI(Tl)
7x7 2.00 50 50
5 NaI(Tl)
2x2 Well-
type
0.90 50 50
6 CdZnTe 0.70 150 0 7 BgO 1.20 130 50 8 HpGe 1.10 230 0
Conclusion: Write down your conclusion on the above observations. Which type of detector is
good for counts and which one is right choice for high resolution etc.