1. The problem statement, all variables and given/known data I have attached a picture of the question. A 2 Ci 137Cs source is equal to 2 x (3.7x1010 Bq) = 7.4x1010 s-1 8 hours a day, 5 days a week and for 50 weeks is a total duration in seconds of 7.2x106 s An 8 cm lead shield = 0.08 m IRR99 regulations set an effective dose limit as 20 millisieverts per year. Therefore, 10% of of their effective dose limit is 2 millisieverts = 0.02 m2s-2 2. Relevant equations None 3. The attempt at a solution [7.4x1010 s-1 x 0.08 m] / 7.2x106 s = 0.02 m2s-2 - d d = 2.4x10-5 m I jiggle the equation about in different ways but keep getting small values for d.