system
Given the following post, respond as if you're commenting on Reddit:
human
What stabilizes a Neutron in a Nucleus from Neutron Decay?

The question is simple, but the answer is difficult.

If you have a neutron in, say, a helium atom... that neutron is stable for billions of years.

Contrast this with a free neutron, which has a half life estimated to be somewhere between 10 and 15 minutes. Free neutrons decay into a proton, an electron and a gamma ray (and an antineutrino or something like that?)

So what is it that makes such a huge difference in the stability of neutrons (in a nucleus vs free)?
gpt
Nucleons in (stable) nuclei are bound, they have less energy than free particles. A helium-4 nucleus has less energy than a helium-3 nucleus plus a proton plus an electron (and also less energy than lithium-4 plus electron). The neutrons cannot decay because there is not enough energy.