Question

Technetium-99m is a radioactive isotope commonly used in medicine as a radioactive tracer. A radioactive tracer is an isotope injected into the body to help create images for diagnosis of health problems. Technetium-99m has a half-life of 6 hours. If a patient receives a dose of technetium-99m one morning, about what percentage of the technetium-99m will be left in the patient's body 12 hours later?
A.

6.25%

B.

12.5%

C.

25.0%

D.

93.8%

Answer 1

After 12 hours that's two half-lives (12 ÷ 6 = 2). Remaining fraction = (1/2)^2 = 1/4 = 25.0%. Answer: C.