An isotope of Tc having a half-life of 6.0 h is used in bone scans. If a certain amount of this Tc is injected into the body, how long does it take for its initial decay rate to decrease BY 99%?
A) 0.060 h
B) 3.3 h
C) 33 h
D) 40 h
E) slightly more than a month

Question

Quizplus · Accepted Answer

The decay rate decreases by 99% when only 1% of the original remains. This corresponds to about 6.64 half-lives (since (1/2)^6.64 ≈ 0.01). Multiplying 6.64 by the half-life of 6.0 h gives approximately 40 h.

An Isotope of Tc Having a Half-Life of 6