1. The problem statement, all variables and given/known data Some people are standing at a distance of 3 m from an unshielded 60Co γ-ray source of activity 10^9 Bq. What radiation dose rate are they receiving? (Each disintegration of 60Co produces a β particle of 0.3 MeV maximum energy with a range 0.8 m in air, and two γ rays, one of 1.2 MeV and one of 1.3 MeV, in quick cascade). 2. Relevant equations dDose/dt = AE/r^2 A = activity E = energy of photons r = distance from source 3. The attempt at a solution I'm at a bit of a loose end with this question as i've not been given any guidance - perhaps someone could suggest a relevant website to explain? Due to the Beta particle travelling only 0.8m does this mean it doesn't reach the people standing 3m away? or does it decay into other particles? Do i at some point calculate the flux of the rays? as i put the r^2 term in as i assumed it to be like a point source and diverging away (thus a 1/r^2 relation) Thanks for any help and guidance on this question!