A nuclear stress test utilizes a gamma-emitting radioisotope such as thallium-201 to follow the flow of blood through the heart - first at rest, and then under stress. The first-order rate constant for the decay of thallium-201 is 9.5 x 10^-3 hr^-1. Calculate how long it takes for the amount of thallium-201 to fall to 5.0% of its original value.

Question

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The half-life of thallium-201 is:t1/2 = ln(2) / k = ln(2) / (9.5 x 10^-3 hr^-1) = 73 hrTo fall to 5.0% of its original value, it will take 3 half-lives:3 x 73 hr = 219 hr

A Nuclear Stress Test Utilizes a Gamma-Emitting Radioisotope Such as Thallium-201