The inverse square law is a law that relates the intensity with respect to the distance of the radiation source. The easy way to think about it is that every time you double the distance from the radiation source, you have to decrease the intensity of radiation by 1/4th.
The formula for the inverse square law is:
Intensity1/Intensity2=(Distance2/Distance1)^2
One easy way to visualize this is to take a look at a light bulb. As you move closer to the light bulb, the light gets brighter and brighter; however, as you get further away from the light, it gets less intense and dimmer. This plays a big role in radiation safety because it demonstrates that as you move further way from the radiation, the smaller the dosage will be.
X-ray X-pert 