|Here at the Centre for Antimatter-Matter Studies we obtain our antimatter from radioactive decay.|
|We start with a version of the sodium atom called sodium-22, which has a different mass from the normal sodium atom, sodium-23.
Ordinary sodium is a common, everyday substance. It’s in the table salt (also known as sodium chloride) you put on your food.
But sodium-22 is a bit different. Because of its different mass, sodium-22 is unstable: left to itself, it gradually turns into neon-22.
It does this by giving off energy and mass, in the form of sub-atomic particles.
In other words, it’s radioactive.
Handle with care
We have to look after the radioactive sodium-22 carefully. Here at CAMS we keep it wrapped in a 5cm-thick layer of tungsten, inside a vacuum chamber.
|The vacuum chamber itself is inside an aluminium tank filled with lead shot, and this provides about another 20cm of lead shielding. (We made the lead shielding ourselves, from almost quarter of a tonne of Number Ten shotgun pellets, which we bought from the Winchester company.)
All these precautions mean that the radiation levels a metre or so away from the tank are only just higher than the naturally-occurring background.
Even so, only people with radiation safety training are allowed into the area, and we monitor the radiation exposure of everyone who works regularly in the lab.
Sodium-22 gradually decays into neon-22, by giving off sub-atomic particles. When it does this, one of the particles it gives off is a type of antimatter: a positron.We use electric and magnetic fields to capture the positrons, so we can run experiments to study how positrons react with ordinary matter.
As far as we know today, the positron is the most common form of antimatter in the Universe, and it’s the particle we use for most of our research at CAMS.