The unstable isotope nickel-59 can be used to date rocks that contain it. Nickel-59 decays into the more stable cobalt-59. The nickel isotope has a half-life of 76,000 years. Which statement about nickel-59 is true?

a) After 76,000 years, all the nickel-59 in a rock decays into cobalt-59. b) Nickel-59 can only be used to date rocks that are younger than 76,000 years. c) All the nickel-59 stabilizes after it completes one half-life period of 76,000 years. d) The amounts of nickel-59 and cobalt-59 remain the same over a half-life period. e) The amounts of nickel-59 and cobalt-59 tell how long ago the rock cooled to closure temperature.

Question

Chemistry

Mr Kitty

7 February, 11:48

The unstable isotope nickel-59 can be used to date rocks that contain it. Nickel-59 decays into the more stable cobalt-59. The nickel isotope has a half-life of 76,000 years. Which statement about nickel-59 is true?

a) After 76,000 years, all the nickel-59 in a rock decays into cobalt-59. b) Nickel-59 can only be used to date rocks that are younger than 76,000 years. c) All the nickel-59 stabilizes after it completes one half-life period of 76,000 years. d) The amounts of nickel-59 and cobalt-59 remain the same over a half-life period. e) The amounts of nickel-59 and cobalt-59 tell how long ago the rock cooled to closure temperature.

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Answers (1)

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Lindsay Downs · Answer 1

The answer is choice E. The decay of Nickel-59 into Cobalt-59 is a continuous process, and the rate of decay is proportional to the remaining amount of Nickel-59. What we observe is the relative amounts of Nickel-59 and Cobalt-59, and this is what allows us to determine the percentage of Nickel-59 that has already decayed to Cobalt-59.