Atomic number: 43
Used in: medical imaging
Criticality rating: not rated
Technetium is exceedingly rare. Until 1937, it was just a hole in the periodic table. When element 43 was finally isolated, it was by the then-innovative expedient of synthesising it, rather than by digging it out of the ground.
That is because technetium, though present within uranium ores in Earth's crust, quickly falls apart through radioactive decay. What frustrated early element hunters is a boon for medical imaging. One of the element's forms, the isomer technetium-99m, has a half-life of just 6 hours – long enough for it to be injected into a patient and light up the body part of interest, but short enough to minimise radiation exposure.
Globally, around 30 million medical procedures involving technetium are performed each year. But two new Canadian reactors which were to secure supplies of technetium and other medical isotopes have been mothballed. So it questionable whether these procedures can continue at the same rate. For now, a handful of ageing reactors supplies the world's hospitals.