about medical tracers

Medical tracers are mostly gamma emitters.

Because pure gamma emitters are few. Thus, some medical tracers are beta/gamma emitters, e.g. iodine-131 for thyroid uptake test. Pure gamma emitters generally are of short half-lives, e.g. technetium-99m, half-life 6 hours, flourine-18, half-life 110 mintes. They need to be produced on-site.

The detector used in detection gamma rays emitted from tracres in organs of the human body is a "gamma camera", which is a scintillation type of detecting instrumen using a large sodium-iodide crystal as the scintillator. The detection efficiency is large enough for the detection of highly penetrating gamma rays.