Fission question (1 Viewer)

[ipicac]

Just wondering if any of you could explain this, maybe you've come across it:

The larger nuclei need more neutrons than protons to remain stable. So then why when adding a neutron to say uranium-235 does it explode in fission? May be something to do with the strong nuclear force ??

any help would be appreciated, thanks

 

[BlackJack]

Yes, there's an optimum ratio of protons to neutrons.
goes from 1 to 1.5 as you go up the scale. However, adding eutrons won't simpkly increase the attraction close to itself... there are also other forces involved.

(additional info) The helium nuclei is the most stable configuration and most stable atoms have groups of 2p/2n and perhaps a limited amount extra n for stablitiy.

The reason U-235 explodes is because of the other forces as well. The momentum of the neutron, when it gets absorbed into the U-235 atom would make it split in different ways... it happens. The constant interaction bewteen p & n and all that gets disrupted, etc... remember beyond a cerrtain distance the force between nucleons becomes negative? That's probably what happens when the incoming neutron attracts other nucleons to itself.

 

[ipicac]

Thanks for the help - so you are saying because the nucleons are now more tightly packed that the distance between them reduces - so the strong nuclear force becomes repulsive ?

ok thanks!

 

[BlackJack]

There's a graph somewhere... What I'm saying is not the the become so clse it becomes repulsive, but in certain arrangements, the vibration will cause an increase in distance in a part of the nucleus so that the force becomes negative. It's quite strange.

I'm thinking the extra neutron pulled/pushed a part of the nucleus away too much...
edit: the nucleus is constantly vibrating because of the binding energy, and with the addition of a neutron, it becomes even more unstable... the mechanism might be explained in university physics...

hmm... can't find the graph now.. come back later...

edit: ahh... this would be where chaos maths coms in, I think... the same effect probably causes alpha decay or something...