5.

82Pb28 is the stable nal daughter of the radioactive series whose parent is 9Th23'2 (see gure below). The half-life of the parent is 1.4 x 1010 yr. A piece of thorium ore containing 1 kg of 90Th232 is found to also contain 200 g of Hszm. (3) Assuming that all of the 82Pb208 in the rock came from the decay of 90Thm, and that none of it has been lost, calculate the age of the rock; that is, calculate how many years have passed since thorium was concentrated in the minerals in the me" and the equilibrium decay began. 92 .- _ ' --EiIII\" 80 _ ____ H aim II. I'- 78 III IIIIIIIEEEE 124 126 128 130 132 134 136 138 140 142 144 Nub- (b) There are a total of six 0: particles emitted in the decay of the radioactive series. Assuming that a negligible number of them could have escaped from the rock because it is so thick, calculate how much helium originating from the ct decays should be in the rock (c) The rst daughter of the series, 88Ram, decays with half life 5. 7 years into the second daughter 89Acw'. Calculate how much \"Rang should be in the rock