I am pretty sure the sun fuses just standard one proton hydrogen. So why do we need to use deuterium and tritium for our bombs?
In: Physics
We use those because they fuse more easily. Technically you can fuse ANY element that is lighter than iron and gain energy from it, but for example to fuse carbon you need MUCH more extreme conditions than for hydrogen fusion.
Protium (standard hydrogen) has MUCH more coulomb force per weight (1 charge per particle), wich means the initial force required to get them close enough together for fusion is a multiple of the force needed to push bigger particles with the same charge together.
It’s a bit like “playing billard with magnetically repulsive balls”. The lighter the balls are the harder it is to get them to actually collide
>I am pretty sure the sun fuses just standard one proton hydrogen.
It in fact does not! the proton-proton chain reaction (also referred to as the p-p cycle) is how stars of similar mass to our own sun get their “start”. As a proto star, the first “thing” that starts to happen is the fusion of two protons to form a deuterium isotop, which releases a small positron and a neutrino, converting one of the protons to a neutron.
The deuterium formation process is a critical step in proto-star development.
Larger stars develop differently, largely because the intense gravitational force is strong enough to overcome the Coulomb barrier.
The sun actually does a 2 step process
It fuses 2 protons, which almost immediately beta decays into dueterium.
After that, it either fuses a proton with dueterium to make helium-3 or fuses 2 dueterium into ordinary helium-4
By starting with heavy hydrogen, we can skip that first step which makes the reaction easier to get going
Technically, you don’t. Practically, however, the required energies are much, much lower if you start at heavy hydrogen than hydrogen-1.
In the Sun, the initial fusion of Hydrogen-1 does not create helium-2 (which is incredibly unstable due to the repelling “electromagnetic force” on protons being able to overcome the attractive “strong force” when no neutron is present). Instead, when 2 Hydrogen-1 fuse they turn into Hydrogen-2, releasing a neutrino and a positron. This requires a lot of input energy and we are not currently capable of doing it on large scales.
The next step is that Hydrogen-2 and Hydrogen-1 fuse into Helium-3, which is stable, and releases gamma radiation as a result. This is where we start for hydrogen bombs, because the input energy required is much lower, and the energy output is quite high. Two Helium-3 then fuse into a Helium-4, releasing 2 Hydrogen-1 in the process, to finish the fusion reaction as completed within the sun. This last step is not done in nuclear bombs at a large scale as the explosion tends to scatter material before it reaches this stage.
Tritium and Deuterium are much more likely to react than just H-1. So reactions run quicker.
Most importantly, they’re abundant. Deuterium is present in sea water, and tritium is made when lithium decays in the incredibly intense neutron bombardment. So by making the fuel lithium – deuteride, you have all the components in one solid form.
It skips a step. The way the Sun fuses actually does involve making heavy hydrogen on the way to making helium, so by starting at heavy hydrogen we skip a step and can save a ton of energy by noting having to fuse it.
Fusion doesn’t really work with just standard hydrogen on earth. The nuclear reaction for it almost always looks like:
>
H + H -> He-2 (with a half life of about 0) -> H + H
To get deuterium you need the He-2 to beta decay, which is governed by the weak force. This is extremely unlikely to occur and only happens in the sun because there is so much hydrogen present. On average a proton takes ~9 billion years to make it past this step.
We don’t have enough hydrogen on earth to rely on this process, so we need to skip this step and just start with the Deuterium.
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