eli5 where does the neutron come from when creating helium in fusion?

Question

I keep seeing things about how protons turn into neutrons but that makes no sense to me. How can the quarks of a proton seemingly change and turn into a neutron? I have a project and I need to know this for both neutron stars and nuclear fusion

In: 3

Answer 1

For fusion reactions here on earth, it is already present in the hydrogen fuel. The most common, and easiest to achieve, fusion reaction is deuterium and tritium. Deuterium is hydrogen, but with a neutron along with the proton, and tritium is hydrogen, but with two neutrons in the nucleus. The fusion reaction is (1p 1n) + (1p 2n) = (2p 2n) + 1n. 2 protons and 3 neutrons in, 2 protons and 3 neutrons out.