Chapter 17 · Radioactivity and Nuclear Chemistry
17.11Radioactivity in Medicine
9 min · two checks
Predict
Why would a physician choose a short-lived isotope as a tracer?
The idea
- Contrast imaging tracers with radiotherapy.
- Explain the half-life tradeoff.
Isotope scanning puts a chemically chosen tracer where the body is doing something of interest — accumulating in bone, being taken up by an active thyroid, tagging a sugar that busy cells consume. The radiation leaving the body is detected and turned into a map. Technetium-99m is a workhorse because it emits gamma rays that leave the body and can be counted, and its half-life is about six hours. PET scans use positron emitters; the positron and an electron annihilate and produce a pair of gamma rays.
Radiotherapy uses radiation to kill tissue, usually cancer, either from a beam outside the body or from a source placed near the tumor. The goal is a dose that cancer cells, which divide often, handle worse than surrounding tissue. Shielding and aim are the whole art. None of these uses change the nuclear rules you already learned. They choose an isotope whose emission, chemistry, and half-life match the job, and they treat the dose as a quantity to calculate rather than a glow to admire.
Keep these
- Tracers report location. Therapy deposits a killing dose.
- A useful tracer emits something detectable and does not linger.
- Half-life, chemistry, and emission type are chosen together.