Where do the neutrons come from when hydrogen turns into helium in nuclear fusion?

Answer 1

In fusion engines we call stars, protons, which are hydrogen nuclei, are forced together and fused to create helium. This happens in early stellar life with the small- to medium-sized stars. When the protons are forced together, the first step involves fusing a pair of protons together with the weak interaction or weak nuclear force mediating the change of a proton into a neutron. Deuterium, or heavy hydrogen, is created. When deuterium reacts with a proton and the pair of particles are fused, a helium-3 nucleus is formed. From there, the reaction possibilities increase and we view what could occur along branches. This is the proton-proton chain reaction that is the basic process in stellar nucleosynthesis. The key to understanding these reactions is the knowledge of the ability of a proton to transform into a neutron through mediation by the weak nuclear force.

Answer 2

When nuclear fusion occurs in the proton-proton reaction, two hydrogen-1 nuclei, (two protons) fuse, and one of the protons will immediately undergo beta decay and become a neutron. That results in the production of a hydrogen-2 nucleus (a neutron and a proton), which we know as deuterium. Next, the deuterium will fuse with another hydrogen-1 nucleus (a proton), and this will create a light helium nucleus (helium-3). Then two He-3 nuclei fuse and create a helium-4 (He-4) nucleus and two hydrogen-1 nuclei.

There are a couple of other routes through which hydrogen can fuse to end up with helium, but this one is probably the "simplest" of them. A link can be found below to review this information and find out about the other options regarding fusion to create helium.

Answer 3

In nuclear fusion, when hydrogen atoms fuse to form helium, some of the protons in the hydrogen nuclei are converted into neutrons through the weak nuclear force. This process is called beta-plus decay or positron emission, where a proton transforms into a neutron, emitting a positron and a neutrino. The newly formed helium nucleus contains the original protons from the hydrogen nuclei and the additional neutrons created during the fusion process.