What makes Uranium-235 ideal for nuclear fission? Why not use another element all together?
In: Physics
Think of atoms as towers made of jenga blocks. You are trying to collapse them (split them up) by throwing a single block at the stack.
Some arrangements, like all the blocks laid flat on the table, can’t easily collapse. They’re as low as they can go already, so splitting them up actually takes energy.
Others might be closer to a normal stack of blocks. Sure, you could knock it over, but it’s not a sure thing and sounds like a lot of work. And since at the end of the day you need one tower to fall into the next and so on (chain reaction) this doesn’t work for you either.
But what if we could arrange a tower, balanced on top of a single block? Surely no matter how you hit it, it would fall. And the pieces of that one should hit similar arrangements nearby.
This is why we pick U-235. It’s unstable enough to fission easily when we need it to, but stable enough that it doesn’t simply decay into other elements in the time it takes to refine. It also has a long-ish decay chain, yielding lots of useable energy (the analogy doesn’t work for this part.)
Reactors have been proposed and/or implemented with other elements, notably thorium, but they are not the prevalent design.
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