I am trying to do a simple calculation on radiation propagation using Cs-137 as an example. Cs-137 has the following properties: Activity = 3.400e+15 Bq/kg Decay energy = 188.096e-12 J (1.174 MeV) This results in 639.526e+03 J/s of radiation, which is then inversly proportional to the distance from the source (or is it squared...I think that was for intensity...?). But...this is at distance 0, so it doesn't work. Could I perhaps somehow use the cross-sectional area of the nuclei? I have a PDF document with algorithms for more accurately calculating radiation propagation, with the specific distance propagated and taking into account absorption by a medium etc., but first I would like to understand the basics. Primarily the inversly proportional thingy, as the energies aren't reference distance at 1 m (or any other reference distance), but at s=0. From there on I should then be able to calculate the absorbed dose, and then the equivalent dose.