The half-life of cobalt-60 is 5.3 years, while that of strontium-90 is about 29

Question

The half-life of cobalt-60 is 5.3 years, while that of strontium-90 is about 29 years. Suppose you have samples of both isotopes, and that they initially have the same activity (number of decays per second). What must be true of the numbers of cobalt-60 and strontium-90 nuclei in these samples?

A) There are more strontium-90 than cobalt-60 nuclei.

B) There are equal numbers of cobalt-60 and strontium-90 nuclei.

C) There are more cobalt-60 than strontium-90 nuclei.

D) It is not possible to compare numbers of nuclei without knowing the masses of the samples.

Explanation / Answer

activity = lambda N

lambda = ln(2)/halflife

so smaller halflife means bigger lambda

so cobalt has more colbalt

C)

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