# Lithium fission

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1. May 16, 2015

### Stephanus

Dear PF Forum,
But there is one thing that intriguing me.
This is one of the reactions that produces tritium.
n + $_3^6$Li -> $_2^4$He + $_1^3$H + 4.8 Mev
What is this reaction called?
1. Fusion? If yes, why it's called fusion?
2. Fission?
3. Other?
Because from here, it looks like a fission to me.
Shooting a neutron to an atom that splits it into two smaller atom.
If this is fission,
Lithium is very far away from iron, right? Shouldn't it absorb massive energy? Why does it produce energy, instead?

Thanks

2. May 17, 2015

### e.bar.goum

It depends on how technical you want to be. I'd call it "neutron capture followed by breakup". Naming reactions like this gets tricky, unless the dynamics are well understood. You don't normally use the word fusion for neutron capture, and you don't generally use the word fission for such a system. Fusion followed by fission also are defined by a certain characteristic timescale,

It produces energy because of the mass difference between the entrance and exit channels. You're probably confused because you're viewing it as a one-step process. Instead consider each part of "neutron capture" and "followed by breakup" separately. n+6Li -> 7Li has positive Q-value of 7.3 MeV, and the subsequent breakup of 7Li into cluster constituents costs about 2.5 MeV, thus giving you 4.8 MeV out at the end.

Last edited: May 17, 2015
3. May 17, 2015

### Staff: Mentor

It is also an odd/odd nucleus (with 3 neutrons and 3 protons), which needs a lot of energy to form. That also means you can release energy by forming the well-bound He-4 nucleus and having the rest emitted as tritium. For those small nuclei, things are a bit more complicated.

Naming is difficult for those reactions.