Question

After the initial cleanup effort at Three Mile Island, approximately 400,000 gallons of radioactive water remained in the basement of the containment building of the Three Mile Island Unit 2 nuclear plant. The principal sources of this radioactivity were Cs-137 at 156 μCi/cm^3 (5.772000 MBq) and Cs-134 at 26 μCi/cm^3 (0.962 MBq). How many atoms per cm^3 of these radionuclides were in the water at that time?

The answer is about 1.78 billion years, but I don't know how to solve for it.

Answer 1

After the initial cleanup effort at Three Mile Island approximately 400,000 gallons of radioactive water remained in the basement of the containment building of the Three Mile Island unit 2 nuclear plant.

Given that:

Volume of the left = 400,000 gallons

we find there are 9. 032 × 10¹³ atoms per Cm ^{​​​​3}