Neutronium

[Jay-qu]

I was just doing some physics questions and then it occurred to me that it was odd that I had never thought of the case of a nucleus that contains no protons - just neutrons. I thought hmm what would be a good name for this - and so typed Neutronium into google, lo and behold I actually got some hits :confused:

 

Although it does come under various names (neutrium, polyneutron) the basic premise is the same - its not observed in nature.. why is this? I thought it would form a rather stable system, what does the proton do to make the system more stable?

 

Once we get this first bit out of the way we can talk about neutron stars :cup:

 

J

[sanctus]

I don't know why on the spot, but about neutron stars, if I remember right, the name is misleading: neutron stars are stars which resist collapse into a black hole via the neutron pressure...

[Qfwfq]

I thought it would form a rather stable system, what does the proton do to make the system more stable?

Actually even a single neutron isn't very stable, half life is only about a quarter hour. For the exact whys and wherefores you need to reach weak and strong nuclear interactions. The single neutron decays by weak interaction, giving a proton, electron and neutrino. Similarly, after an atomic nucleus beta decays it has one less neutron and one more proton.

[Jay-qu]

So what dictates that a nucleus will decay via either beta- or beta+? I know its so it reaches the so called stability line, but what makes that line stabe?

[Jay-qu]

After some reading I came accross a few terms that I have never heard before.. one been 'magic numbers' - number of nucleons that make a particularily stable nuclide [2,8,20,28..] and a proposed shell model for the nucleus.

 

Does anyone understand the concept of magic numbers and knows where they come from?

[InfiniteNow]

I cannot say I fully understand it, but have you looked at the following?

 

Shell Model of Nucleus - Magic Numbers

 

[Jay-qu]

Yeah I have, its in our atomic physics 201 notes.. but Im struggling to make sense of why when you see these numbers fall out the end, it means they are more stable states :confused:

[Guest Lambus]

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[Qfwfq]

Does anyone understand the concept of magic numbers and knows where they come from?

Well I've never taken actual nuke courses but AFAIK it's analogous to the noble elements in the periodic table.

[Jay-qu]

apparently its not.. Ca-40 and Ni-48 are two counter examples of that

 

You are talking about the shells been full no? Those are a different set of magic numbers.. 2,8,18..

[Guest Lambus]

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[Qfwfq]

apparently its not.. Ca-40 and Ni-48 are two counter examples of that

If you meant that about my point, I didn't mean that nuclei with the magic numbers must be the noble gasses. The number of electrons (=Z) isn't the same as the numer of nucleons (>Z), also the degeneracy removals don't seem to have the same crossovers and I wouldn't expect them to, either.

[Jay-qu]

I see.. it could take a while to get my head around this stuff. But im begginning to think that Im hitting the limit of understanding without learning more about the strong force (if not the limit of everyones understanding..)

[Qfwfq]

Har! Some folks have investigated these things pretty deeply but certainly QCD is as sticky as ya could expect it to be with all those gluons glitching around in it. It's just about past (current?) computational capabilities but not beyond understanding. ;)

[Guest Lambus]

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[Qfwfq]

Er, despite the note

The English used in this article may not be easy for everybody to understand.

I think the English in that page is ordinary enough.

 

However (although my studies of QCD were a bit on the basic side) I'm under the impression that whoever wrote that wiki got a few of the facts a bit scrambled up.

[Jay-qu]

[risidual strong force] is what holds the nucleus of an atom together.

 

this sounds somewhat the same as:

 

[the nuclear force] is responsible for binding of protons and neutrons into atomic nuclei

 

so whats the difference?