# Nuclear physics question

## Homework Statement

A rock contains three 207Pb nuclei for every 235U nucleus. Determine the age of the rock assuming all of the 207Pb was formed through the decay of uranium. (The half life of 235U is 0.71x109).

N=N0e-λt

## The Attempt at a Solution

So the decay constant is ln 2/T1/2=9.76x10-10. So

N0 = 1 e(9.76x10-10)t

But the problem is I don't know how to find N0, the remaining nuclei. How could I find it using the information given? They just say there are 3 Pb's for every uranium nucleus... How do we find the amount decayed so we can subtract it from the total to get the remaining N0?

SteamKing
Staff Emeritus