Find out how a particle accelerator will be used to make rare isotopes used for nuclear medicine.
Technetium 99m sounds like something in a bad fifties science fiction film that would be injected into someone to give them psychic powers, or 12 hours, or both. This goes double when it’s combined with the ominous phrase ‘nuclear medicine’. Together they call to mind a hapless tourist being held down by a hulking orderly named Nurse Mugsy while a guy with salt and pepper hair and a lab coat brandishes a glowing syringe and talks about how the only way humans will survive the coming nuclear winter is by spiking the water supply with technetium 99m. It may or may not be raining, depending on the sensibilities of the director.
The realities of nuclear medicine aren’t that much brighter. Technetium 99m and nuclear medicine are not fun things to experience. The isotope is radioactive, and throws off x-rays from inside a person’s body. X-rays go through flesh like it’s not even there, so the technetium 99m inside a person is measurable from outside of the person’s body. In medicine it is often added to a chemical that will attach itself to tumours or growths inside a person. That chemical attaches itself to the tumour, and technetium 99m’s x-rays allow doctors to see how big a tumour is without having to cut that person open. Being a human x-ray projector is much, much better.
Seriously, though, technetium is both massively useful and massively used. The problem is, x-rays are not thrown off because an element is planning to stick around. They are tossed out as an unstable atom becomes more stable, and the isotope technetium 99m doesn’t have a long shelf life. This means that the has to be a way of getting it. Nuclear reactors are able to produce it, but they are not the safest things around.
Canada, perhaps encouraged by the fact that the Large Hadron Collider did not turn out to be a doomsday device, has come up with a plan to build a particle accelerator in order to make and harvest technetium 99m. The accelerator will hurl a stream of electrons at a metal target. Once at the target, the electrons will either swerve off course or stop dead in their tracks in the comical fashion of Wyle E Coyote, after he has been fired at a wall in a Warner Brothers cartoon.
‘Bremsstrahlung’ comes to us courtesy of the Germans, who are fresh off their win with schadenfreude and looking for other compound words to popularise. It means ‘braking energy’. When the electrons swerve off course or stop at the target, they lose momentum, thus losing energy. Any hippie will tell us that, like, energy goes on forever, man, and can never really be lost, and of course hippies are never wrong. To conserve energy, some photons are produced to make up for the energy lost by the electrons. The electrons whizzing by also mess with the electromagnetic fields at the target, producing even more photons.
These photons form another beam which hits another target, this one made of heavy elements. These elements break down, producing rare isotopes. Those isotopes, including technetium 99m are harvested and used in nuclear medicine. Possibly also by a nurse named Mugsy. People will call their kids anything these days.
Top image of facility for rare isotope beams at at Michigan State.