SOLVED: Point sources of gamma radiation follow the inverse square law, which states that the intensity of the radiation decreases in proportion to the inverse of the distance from the source squared.
How Much Radiation Does it Take to Kill You? - Dan's Wild Wild Science Journal - AGU Blogosphere
South gamma radiation exposure calculator, cardboard - Hocker Incorporated
Student Highlight: An Analysis of Radiation Dosimetry in Hulk | RAMP Website