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.