How Long Can a Neutron Survive Outside an Atom?

How long can a neutron survive outside an atom?

Neutrons are probably best known for being a chargeless component of the nucleus of all atoms other than hydrogen. In that context, they can be extremely stable—you probably noted the fact that your body wasn’t decaying around you. But pull neutrons out of that context, and they become very unhappy.

They’ll decay into a proton, an electron, and a neutrino. That decay has a half life—the time it would take half the neutrons in a large sample to decay—of a bit under 15 minutes. But just how much less isn’t clear.

That’s not for lack of measurements. We have plenty of them, many with error bars of less than three seconds. The problem is that these measurements systematically disagree.

Getting that to the point where the difference is five standard deviations—a value that physics accepts as indicating an effect is real—requires cutting down on those errors. And that’s exactly what the new US-Russian work aims to do.