Experiment – 1

(This should be carried out only by RADLab software)

Objective : Study of Geiger-Muller Counter characteristics curve and counting statistics by -ray

source.

Sources : -ray source

Scope of Expt : It has two part

(A) Draw the operational characteristics curve of the counter, showing threshold, operating voltage and

the onset of break-down. There should be at least 30-50 points on the curve.

(B) Study the distribution curve of the counts from radioactive decay. Find mean value and standard

deviation ().Take at least 300 ~ 350 points.

Theory : Write theory for GM counter in details. Read various literatures given to you or from books and

internet etc.

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-1. You need the following items. 1) A Gamma-ray source 2) A GM tube 3) High Voltage source 4) A counter Now go to Administration, then click on “Create Experiment”

Now, Select Experiment Type :

o Gamma Experiment Now

Now, Select Source Type :

o Cs-137 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 Geiger Muller Now How does a GM tube 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 instrument. 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 NIM Module :

o HV Supplier o Counter

Now You can select / choose multiple NIM module just by

pressing ctrl + NIM Module

You can give Experimental Name : Expt 1 Also choose Experimental Sheet as text : Expt 1 A documentation file in .html is not available

currently for Expt 1 and in future we shall make it. In

that case you can upload / choose the other option i.e

Experiment Sheet (as html).

> Next

Now, verify your selection i.e Detector, Source, NIM Modules etc. Now

Now go to File --> Select Experiment --> Expt 1 Now After that click on You can transfer all of them to your work bench just by clicking on “Cs-137” then clicking on “work bench”. Transfer all the four (4) instruments to your work bench.

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

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).

Finish

Select

Instrument

Cables

Run

A) Operational characteristics curve of GM Tube.

(i) Set counting time for 1000 unit (it’s not exact unit of second) or more. (ii) Clear the counter so that it should show 0. (ii) Set your source in line with GM tube. (iii) Set your HV to 0.0 kV by turning the HV key. Don’t forget to switch ON HV supply. (iv) Now go to view and click on Draw particle path (this is optional). (v) Now RUN. Note your counts. This is RUN-1 (vi) Repeat the same for RUN-2 and note down your counts. (vii) Increase your HV in a step (see the step size for different region) and take RUN-1 and RUN-2. Note it down in your record. (viii) Repeat (vii) in a step of 0.1 kV [from 0 to 0.75 kV], step of 0.01 [from 0.75 kV to 0.95 kV], step of 0.1 kV [from 1.0 kV t 3.0 kV]. (vii) Make proper table and draw the graph.

HV

(kV)

No of Counts Average

Counts

HV No of Counts Average

Counts Run-1 Run-2 Run-

1

Run-2

0 Step : 0.05

0.1 1.0

0.2 1.05 Step : 0.1 1.10

0.75 Step : 0.05

0.76 2.0 Step : 0.01 Step : 0.05

0.94 Step : 0.05

0.95 3.0

Plot characteristic graph of GM Tube:

B) Study of distribution curve of the counts :

(i) Set operating voltage as HV = 0.96 kV (or you can keep middle of the flat portion of graph)

(ii) Set counting time for 100 unit (it’s not exact unit of second) or more. Set no. of run as 1. (iii) Start counting and note down the counts. (iv) Repeat (iii) atleast 300 to 350 times. More events its better. (v) Make a table: No of counts for a bin size vs Frequency of counts. Use origin to choose the bin size.

(vii) Plot No of counts vs Frequency of counts and fit it with a Gaussian distribution for a large events.

It should be a normal distribution (discrete due to events) but one can fit a continuous function for large

event number.

F(x) =

No of Counts

Frequency Of counts

No of Counts

Frequency Of counts

539 10 546 42

540 12 547 36

541 15 548 27

542 22 549 24

543 26 550 17

544 35 551 14

545 40 552 11