p43_063 - atoms was N U = N U + N Pb = 1 . 06 10 19 + 6 ....

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
63. (a) The mass of a 238 U atom is (238 u)(1 . 661 × 10 24 g / u) = 3 . 95 × 10 22 g, so the number of uranium atoms in the rock is N U =(4 . 20 × 10 3 g) / (3 . 95 × 10 22 g) = 1 . 06 × 10 19 .T h em a s so fa 206 Pb atom is (206 u)(1 . 661 × 10 24 g) = 3 . 42 × 10 22 g, so the number of lead atoms in the rock is N Pb =(2 . 135 × 10 3 g) / (3 . 42 × 10 22 g) = 6 . 24
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: atoms was N U = N U + N Pb = 1 . 06 10 19 + 6 . 24 10 18 = 1 . 68 10 19 . (c) We use N U = N U e t where is the disintegration constant for the decay. It is related to the half-life T 1 / 2 by = (ln 2) /T 1 / 2 . Thus t = 1 ln N U N U = T 1 / 2 ln 2 ln N U N U = 4 . 47 10 9 y ln 2 ln 1 . 06 10 19 1 . 68 10 19 = 2 . 97 10 9 y ....
View Full Document

Ask a homework question - tutors are online