Physical protection - nuclear radiation

Protocol for measurement of nuclear radiation

Safety rules:

• Place the source in an appropriate container (i.e. nuclear radiation – lead container)
• Use the source only during the experiment; immediately after the experiment place it back in the safety container
• Do not touch the active part of the source (the isotope emits gamma radiation)
• Assure a maximum distance between you and source (keep the source as far as possible from your body)

Materials:

• Scintillation counter
• PC; MS DOS operating system; poisson.exe
• Radioactive source in a lead container
• Shields: Pb, Al, Cu, plastic

Procedure:

A. Performing the measurements:

1. connect the interface to the PC (red led ON)

2. start „poisson.exe”

• <F3> = select the maximum number of measurements
• <F4> = select the timegate

3. draw a table for all your measurements:

4. measure the natural found of radiation and write the values in your table; this value will subtracted from all measured values.

• <F1> = start/ stop new measurement (it is shown the graph with no of pulses for each measurement)
• <ESC> = back to the main menu
• <F6> = evaluate in graph (measurements are shown as a histogram)
• <F4> = set on the graph the mean values
• <ALT> + <F4> = show on the screen the mean values

5. place the source under the detector.

Attention! The source should not be moved from the initial place, in order to keep the same distance betweent the source and the detector for all the measurements

6. measure the number of pulses for the source without any shield and write the values in your table

7. measure the number of pulses for the source covered with the following shields: Pb, Al, Cu, plastic; write the values in your table

8. measure the number of pulses for thicker shield of lead: 2xPb, 3xPb and 4xPb; write the values in your table

9. place back the source in the safety container

B. Calculate the shield effectiveness

1. calculate the effective number of pulses from the source without and with shielding:

Effective no of pulses = [(no of pulses from source ± shield) – NF]

where, NF = natural found

2. calculate the shield effectiveness using the following formula:

E = [(N₀ – N_shield)/ N₀] x 100

where, N = number of pulses from the source with shielding, N₀ = number of pulses from the source without shielding

3. write the obtained value in your table.

C. Calculate the attenuation coefficient, μ in the case of lead shielding against nuclear radiation

1. plot the number of pulses from the source with lead shielding against the thickness of lead shield according to the exponential decay law

2. identify half-value thickness, T_H corresponding to N₀/2 value

3. calculate the attenuation coefficient, μ using the following formula:

μ = ln2/ T_H

ln2 = 0.693