66PE

Problem

Data from the appendices and the periodic table may be needed for these problems.

Unreasonable Results A nuclear physicist finds 1.0 µg of 236 U in a piece of uranium ore and assumes it is primordial since its half-life is 2.3×107 y . (a) Calculate the amount of 236 U that would had to have been on Earth when it formed 4.5×109 y ago for 1.0 µg to be left today. (b) What is unreasonable about this result? (c) What assumption is responsible?

Solution 66PE

- initial mass of Uranium is 7.7 x 1049 kg
- The initial mass of the Uranium is extremely large that seems unreasonable because that much mass is even greater than the entire Milky Way galaxy.
- The assumed half life is very small and hence responsible for the unreasonable result. The half life of the U-236 must be larger than the assumed value.