Wielding proton beams and lasers, physicists have for the first time unlocked one of the key secrets of the rarest naturally occurring element on Earth: astatine.

It's so rare that until recently, researchers had never managed to gather enough of it to test how it interacts with electrons.

That's a problem, in part because one of its radioactive isotopes, astatine-211 has the potential to be useful in cancer therapies.

But researchers weren't sure how likely it is to attract electrons and form negative ions, which could be harmful to healthy cells.

For this effort, the researchers fired the protons at a target made of atoms of thorium, an unstable element with 90 protons?

Focused light can knock around the electrons on an atom, allowing researchers to make precise measurements of their behavior.

Together, those two numbers form a complete picture of how the heavy, rare element interacts with electrons.

Astatine-211 releases alpha particles as it decays, radioactive barbs made up of protons and neutrons that can kill cancer cells.

But determining how to use radioactive astatine salts in cancer therapies demands a deep understanding of how the element creates negative ions.

As astatine snags electrons from molecules in healthy cells in the body, it turns them into negative ions, which can harm healthy cells.