Penetration

     Objective
      To demonstrate the interactions of alpha, beta, and gamma radiation with matter, 
      thus deducing the penetrating abilities of each radiation.

     Materials
          Radiation sources: 
              Po-210 (alpha source) 
              Sr-90 (beta source) 
              Co-60 (gamma source) 
          Geiger counter 
          Absorber set 




                                                                                                          
      
      Procedure 
       Part A 
      1. Place alpha radiation source on a source holder. 
      2. Set Geiger counter to x1 scale and turn on the power. Allow the instrument 
          to warm up for a few minutes. 
      3. Record background activity. 
      4  Insert a piece of paper between the GM tube and the source.
      5. Note the sudden decrease in count rate which is close to the background count rate.

      Part B 
      1. Replace the alpha source with the Sr-90 (beta source). 
      2. Check Geiger counter for x1 setting. 
      3. Arrange the aluminium absorbers according to thickness with the 
          least thick first. Place the first sample in the material holder. 
      4. Plot a graph for this activity. 

     Part C 
      1. Replace the beta source with Co-60 (gamma source). 
      2. Check x1 scale position on the Geiger counter. 
      3. Arrange the lead absorber according to thickness with the least thick first. 
          Place the first lead sample in the material holder.
      
     Do you know?
    1. Why allow time for the Geiger counter to warm up? 
    2. Is it necessary to take background readings every day? Explain. 
    3. What type of results would you expect if the same alpha sample was 
         doubled in quantity? 
    4. Is lead an effective shield for beta radiation? Explain. 
    5. What results would you observe if you had used aluminum for shielding beta rays? 
    6. What materials, other than lead, are effective for shielding gamma radiation? 
    7. What amount of lead is needed to reduce gamma radiation to one-half of a 
         previous intensity count? 
    8. What general statements can you make about the thickness of the absorbing 
         material on the count rates?


        

    
    Analysis

Penetraing power

     There is a great difference in the penetrating powers for alpha, beta, and gamma rays. 
     Of the three types of radiation, alpha particles are the easiest to stop. A sheet of paper 
     is all that is needed for the absorption of alpha rays. However, it may take a material with 
     a greater thickness and density to stop beta particles. Gamma rays have the most 
     penetrating powers of all three radiation sources.


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