Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Quantum_Vaccuum on 09/10/2007 21:11:11
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Uranium-238. It is a very stable element, with an amazing long half-life of 4.7billion years, but still radioactive. But, on the other hand, Uranium-235, an Uranium isotope, is highly reactive and with a few less nuetrons, has a half life of 12.5 million years, which i verry small in comparison that Uranium-238 has 4.7billion years. Why do so little chargless nuetrons matter so much in the radioactivity, and life of an element?
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There's a sort of sability curve for the how stable an atom is, in terms of a ratio between the number of protons and the number of neutrons. The curve is exponential I think, so a few neutrons can radically change the stability of an atom which is already unstable.
As to why this happens, I guess that it's something to do with the "strong forces" between neutrons and protons, and that it upsets the balance further?
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I'm certainly not a particle/nuclear physicist, but this is how I like to think of it.
The point of neutrons is to act as a buffer between positive charges.
Hydrogen has only one proton. It doesn't need that buffer, so entropy dictates that the neutrons will not combine with the protons.
From helium on up, there are at least two protons (which tend to repel each other) in the nucleus. Two protons right next to each other will repel each other a lot. You need something else in there to provide some extra nuclear glue and act as a buffer against each other. Initially, you need about 1 neutron per proton to provide this buffer.
Eventually, trying to pack all those positive charges into such a small region of space, you start requiring more neutrons to provide more buffering activity. This tends to happen right around calcium. After that, you start needing more than 1 neutron per proton. By the time you get past bismuth, it doesn't matter how many neutrons you put in - you still get an unstable nucleus (it's radioactive).
Dick