Explain me what the nuclear isospin is?

[ghery]

Hello:
Can you please explain me what the nuclear isospin is?. Is it a new kind of angular momentum?, and how was it detected ?

Regards

 

[malawi_glenn]

Nuclear isospin is a symmetry property of the nucleons; proton and neutron. The isospin says that the proton and neutron have same strong interaction. One regards the nucleons as spin-up or spin-down in an abstract space called isospin space. And this space follows the same algebra as the spin-space for spin1/2 particles like the electron.

So the proton is usally assign to be the spin-up state in the isospin space, and the neutron with the spin-down state.

You can also have isospin for the u- and d-quarks, the consituents of the nucleons. Here is a good summary if you don't want to buy a textbook: http://en.wikipedia.org/wiki/Isospin

 

[lasm2000]

If you are comfortable with quantum mechanics and spinors then the chapter on Gordon Baym's Lectures on Quantum Mechanics should really set the issue, there is an even more accesible discussion in David Park's book (I think is called Introduction to Quantum Theory). Otherwise the article in wikipedia is rather clear.

 

[julian]

It was right after the discovery of the neutron in 1932, the strong similarity between the proton and the neutron led nuclear physicists to interpret both particles as two states of the same particle! The masses of the proton and the neutron are nearly equal. There is a small difference but this was put down to the different electromagnetic interaction of the two particles. Thus the two particle's masses, to a good approximation, were taken to be equal with respect to the strong interaction.

The variable which distinguishes between the proton and the neutron only takes on two states - just like the spin of certain particles! This led to describing the situation by the same maths as that which describes the quantum mechanics of spin 1/2 particles!

ian

 

[julian]

I think in chapter 10 of the third volume of the Feynman lectures he explains that any two state systme, whatever the original physical situation, it is formally equivalent to a spin-half problem. That's where the spin in isospin comes from - so it doesn't have anything to do with angular momentm

ian