How Many Atoms per Cubic Centimeter Are in Radioactive Water After Cleanup?

[NucE]

Homework Statement

"After cleanup at 3 mile island approximately 400,000 gal of radioactive water remained in the basement of the contaminated building. The principle sources of radioactivity were 137 Cs at 156E-6 Ci/cubic cm. How many atoms per cubic cm were in the water ?

Homework Equations

Not sure...

The Attempt at a Solution

6.022E23 * 156E-6/137 = 6.86E17

 

[mgb_phys]

It's a little more complicated than that.

A Curie (Ci) is 3.7E10 decays/second - so there are 156E-6 * 3.7E10 decays/sec/cc.

Then you need the activity or half-life of Cs137 to know what chance there is of a decay in a second for one atom, or alternatively how many atoms there needs to be to give the above overall decay rate.