A radioactive material has a half life of 4.6 minutes.  After 8.1 minutes, which percentage of the original number of atoms will be left in it? Keep three significant digits.

solve for c)

9. A rock that contains 1.2x10-12 mol of 232Th (t1/2 = 1.4x1010 yr) has 4.2x105 fission tracks, each track representing the fission of one atom of 232Th. How old is the rock?

Time 0 t₁2 20₁2 3₁/12 Number of nuclides, N x 10³ 1000 750 500 90/2 10/₁2 250 125 0 12 212 312 412 512 612 7h2 8h2 9h12 10/2 Time in multiples of t₁/2 The figure shows a typical radioactive decay (amount of undecayed nucleus (N) vs. time (t)) from a heavy nucleus. Such a decay may be best expressed by an equation like : ON = N₂ (xt) ON=N₂/λt -λt ON = N₂e N = N₂ e-1/At N 1,000,000 500,000 250,000 125,000 62,500 31,250 15,625 7,813 3,906 1,953 977 412 5/₁/2 61₁2 7h2 81/2

You inherit 32 kg of cesium-136 after your roommate moves out and leaves it behind. Cesium-137 has a half-life of 30 years. If you pack it in a box and forget about it, but your grandchildren finds it in the attic 90 years from now, how much of the sample is still cesium-137?