Three radioisotopes are being discussed in a chemistry class. Technetium-99m has a half-life of 6 hours. Rubidium-87 has a half-life of 50 billion years. Which describes who would most likely use each isotope?
Answer
A
A geologist would use technetium-99m because short-life indicates an older organism, and a doctor would use rubidium-87 because it allows for a more-accurate measurement of disease.
B
A doctor would use technetium-99m because a short half-life indicates a quick measurement, and a geologist would use rubidium-87 because a longer half-life means that there is a longer time to measure old rock.
C
A doctor would use technetium-99m because a short half-life indicates a quick measurement, and an archeologist would use rubidium-87 because anything containing carbon also contains rubidium.
D
A geologist would use technetium-99m because a short half-life indicates an older organism, and an archeologist would use rubidium-87 because anything containing carbon also contains rubidium.
Explanation
Technetium-99m’s 6-hour half-life makes it useful in medical imaging: it can provide a measurement over a short period and then decay relatively quickly. Rubidium-87’s half-life of 50 billion years makes it useful to geologists for dating very old rocks. The other choices assign the isotopes to unsuitable uses or give incorrect reasoning about what their half-lives indicate.
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