Three Principles of Radiation Safety

  1. Time
    1. Radiation exposure is a linear relationship
    2. Time and exposure are directly related
    3. The longer a person is exposed, the greater the amount of radiation received
    4. Therefore, the more efficient the technologist is when working in a radiation area the less he/she will receive.
    5. Application of time and radiation exposure
      1. Example: 100 mR/hr is being emitted from a radiation source within the work area. If the technologist normally takes 30 minutes to complete his/her task in the work area, then 50 mR is the amount of exposure. However, if the technologist reduces the amount time in the radiation area to 15 minutes, then the total exposure is 25 mR/hr
      2. Calculation to the above statement
        1. (100mr/hr)/(60 minutes/1hr) = 1.67 mr/minute
        2. 30 minutes of exposure = 1.67 * 30 = 50 mr total exposure
        3. 15 minutes of exposure = 1.67 * 15 = 25 mr total exposure
  2. Distance
    1. Radiation exposure can be reduced by increase the distance from the source of radiation. This can be explained by the application of the inverse square law

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    2. Inverse Square Law
      1. A source of radiation or intensity (I) at a distance (D) from a radioactive source has an "inverse square" relationship
      2. Example: At a distance (D) of 1 meter, a source of radiation (I) emits 100 mr/hr. If you increase the distance 1 meter to a distance of 2 meters, then the amount of radiation (i) decreases to 1/4 or 25 mr/hr. Appropriately stated, "The source of radiation decreases inversely square to its point source."
      3. Applying the inverse square relationship shows that the new distance of 2 meters is first inverted to 1/2 and then squared 1/4. This results in a reduction of exposure to 1/4 of the original amount at 2 meter. Therefore, amount be emitted is reduced to 25 mr/hr when the distance is doubled
      4. Inverse Square Law Formula
        1. I(D)2 = i(d)
        2. Where I is the original amount of radiation and D is the original distance
        3. And where i is the new intensity and d is the new distance
        4. The following calculation is applied
          1. I(D)2 = i(d)2
          2. (100 mr/hr) (1 meter)2 = (I) (2)2
          3. 25 mr/hr = I
        5. Additional Example
          1. At one meter, Ted the Technologist reads that the activity level from a source is 40 mR/hr. What is the activity reading at 2 meters away from the source?
          2. I = 40 mR/hr, D = 1 meter, d = 2 meters, i = ?
          3. 40 mR/hr * (1 m)2 = i * (2 m)2
          4. 40 mR(m)/hr = i * 4 m
          5. 10 mR/hr = i
          6. Answer: The activity level at 2 meters from the source is 10 mR/hr
        6. Conclusion: Whenever possible, a technologist should increase his/her distance when working with a radiation source.
  3. Shielding - Refer to your previous lecture on Attenuation

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