Understanding the Unbound Nature of the nn-Pair in Nuclear Clusters

[malawi_glenn]

Why is the nn-pair unbound? I don't seem to find the answer in any of my textbooks =/

 

[mathman]

Why is the nn-pair unbound?

What do mean by "unbound"? If you are wondering why there is no such entity as a double neutron, there is nothing to hold two neutrons together.

 

[malawi_glenn]

That was a very good answer, not. Do you think I am that noob on physics that I have not figured it out my self? Saying that something is unbound and "there is nothing that can hold it togheter" is pretty much saying the same thing.

Someone who has studied nuclear physics who can help me? mathman seems to be a retired mathematician..

I was thinking that neutron + neutron has isopspin 1 and the deutron (the bound state of neutron + proton) has isospin 0. So does it has something to do with that?

 

[Rade]

To malawi_glenn:

While it is true that N-N pair is not "bound" in free state (as you say due to isospin constraint), this does not mean it does not exist as a nucleon cluster state in isotopes as a type of resonance:

1. The di-neutron (N-N) was suggested as a cluster structure moving around some isotopes as long ago as 1969 by L. Pauling:
http://www.pnas.org/cgi/reprint/64/3/807.pdf

2. Di-neutron cluster structure has recently been suggested in He-8 isotope (see page 8 for explanation of what is means to say N-N cluster may exist):

http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.2120v1.pdf

and here for He-8:
http://www.ujp.bitp.kiev.ua/papers/460302p.pdf[/URL]

3. Also for He-6:
[PLAIN]http://www.maik.ru/abstract/nuclphys/0/nuclphys10_0p1724abs.htm[/URL]

4. Di-neutron cluster predicted in O-18 isotope:

http://prola.aps.org/abstract/PRC/v16/i1/p475_1

5. Di-neutron long ago was predicted to be a by-product of certain fission events:
[url]http://www.nature.com/nature/journal/v165/n4201/abs/165722a0.html[/url]
but I have no idea if the experiments suggested have been conducted.

6. See also "halo nuclei" literature:

http://theory.gsi.de/hirschegg/2003/Proceedings/Al-Khalili_131.227.115.66_alkhalili.pdf
[PLAIN]http://www.ingentaconnect.com/content/maik/10637788/2000/00000063/00000010/00000965[/URL]

Hope these links are of some use to you.

 

[malawi_glenn]

Thanx, yes they can exists in cluster. But I was reffering to the analogy with the deutron only.

Thanx again, will look at the links :D