Penetration power of radiation


This practical lesson covers:

  1. How to determine the penetration capabilities of alpha, beta and gamma radiation

Investigating the penetrating capabilities of alpha, beta, and gamma radiation


Aim:

To determine the penetration depths of alpha, beta and gamma radiation through various materials. 

Background information:

Radiation penetration power varies among alpha, beta, and gamma rays due to differences in their physical properties. In this practical, you will investigate the penetration depths of these three types of radiation through different materials. Using a controlled setup with a radiation detector, like a Geiger-Muller tube, you will measure radiation count rates with and without various absorbers placed between the source and detector.

Variables:

  1. Independent variable - Absorbing material  
  2. Dependent variable - Count rate
  3. Control variables - The source should remain the same distance from the absorbing materials, same source for each investigation

Equipment:

  1. Alpha source
  2. Beta source
  3. Gamma source
  4. Radiation detector (such as a Geiger-Muller tube with counter)
  5. Various materials of differing thickness (Such as paper, aluminium foil, lead)
  6. Stopwatch

Method:

  1. Connect the Geiger-Muller tube to the counter. Turn on and record the background count without a source present for 1 minute.
  2. Place the radiation source at a distance of 10cm from the Geiger-Muller tube. Record count, for 1 minute, with no absorbing material between the source and the detector.
  3. Place an absorbing material between the source and the Geiger-Muller tube and remeasure the count for 1 minute.
  4. Repeat step 3 for all absorbing materials being tested.
  5. Repeat steps 1-4 for each type of radiation source.
  6. Calculate the corrected count by subtracting the background count from the count rate for each measurement.
  7. Draw a bar graph of Corrected count vs material for each type of radiation.
  8. This experiment could also be repeated using the same material but varying the thickness of absorbing material.

Safety precautions: 

  1. Never direct radioactive sources towards someone. 
  2. Handle radioactive sources with tongs.
  3. Minimise the exposure time by only removing sources from their lead lined boxes when in use.

How does the student calculate the corrected count?

corrected count =count background count​
corrected count = background count − count
corrected count = count − background count
corrected count = count × background count

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The student records 26 as the background count after 1 minute. The student then records a count of 540 after 1 minute with the source present. Calculate the corrected count for 1 minute.

514 

26

540

566

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The student places an aluminium sheet between the source and the Geiger-Muller counter. The count in 1 minute has not changed compared to with no aluminium sheet present. The source is a emitter.

gamma

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A radioactive source has a corrected count of 125 in one minute with no absorbing material present. Three different absorbing materials are then placed between the source and the detector. Which will be the best absorber?

the material which causes the corrected count to decrease the least

the material which causes the corrected count to increase

the material which causes the corrected count to decrease the most

the material which does not change the corrected count

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Alpha, beta and gamma all have different penetrating capabilities. Put them in order of increasing penetration capability.

Beta, Alpha, Gamma

Gamma, Beta, Alpha

Alpha, Gamma, Beta

Alpha, Beta, Gamma

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