Inverse square law

Last revised by Dr Daniel J Bell on 01 Apr 2020

The inverse square law describes the principle of dose reduction as the distance from the source increases.

This assumes a point source. If radiation spreads over a spherical area, as the radius increases, the area over which the dose is distributed increases according to

A=4πr2

where A is the area and r is the radius of the sphere.

Therefore, the dose is proportional to the inverse of the square of the radius. Thus if you double the distance you reduce the dose by a factor of four.

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Figure 1: inverse square law
    Drag here to reorder.
  • Updating… Please wait.

     Unable to process the form. Check for errors and try again.

     Thank you for updating your details.