A person moves 1 meter to 2 meters from an unshielded Cesium-137 source made of cesium chloride. What percent reduction of radiation exposure will the person experience?
A 50.0%
B 75.0%
C 87.5%
D 88.9%
Correct answer B. The dose of radiation received by a person during a specific amount of time from an unshielded source of radiation that emits gamma rays or X-rays is inversely proportional to the square of distance between the person and the source. This is based on the inverse square law that is further described in the below online reference. The dose of radiation absorbed by the person 2 meters away from the source is decreased to 25% (75% reduction) from what it would have been at 1 meter assuming the duration of exposure is unchanged.
References:
Radiation Safety by J. S. Ballard.https://openoregon.pressbooks.pub/radsafety130/chapter/inverse-square-law/ (Accessed on 2/6/2023. is licensed under a Creative Commons Attribution 4.0 International License)
Wikipedia Web Portal. Inverse Square Law. https://en.wikipedia.org/wiki/Inverse-square_law. Accessed on 2/6/2023 “The inverse-square law generally applies when some force energy or other conserved quantity is evenly radiated outward from a point source in three-dimensional space. Since the surface area of a sphere (which is 4πr2) is proportional to the square of the radius as the emitted radiation gets farther from the source it is spread out over an area that is increasing in proportion to the square of the distance from the source. Hence the intensity of radiation passing through any unit area (directly facing the point source) is inversely proportional to the square of the distance from the point source.”
Contributed by: Jonathan Meadows DO MS MPH DTM