# Pauli exclusion regarding nucleons

• dimwatt
In summary, the conversation discusses the concept of deuteron being an isosinglet and its relation to the isotriplet that includes pp and nn. The speaker also brings up the question about how atoms like He3, which has two protons bound in the nucleus, do not violate Pauli exclusion. The answer lies in the fact that the deuteron is a 3S1 state where the nucleons have the same spin, while in He3, the spins of the two protons are opposite. This allows for the two protons to be in a bound state without violating Pauli exclusion.
dimwatt
I think this is more or less a quick question.

So deuteron (pn) is an isosinglet in the state $|00> =\frac{1}{\sqrt{2}}(pn-np)$ since it cannot be part of the isotriplet that includes pp and nn, since these violate pauli exclusion. That's fine.

So how is it that we can have atoms like $He^3=ppn$? How does this not violate Pauli exclusion with two protons bound in the nucleus (both with isospin state $|\frac{1}{2} \frac{1}{2}>$). It makes some sense if I think of this as a bound state of a proton and deuteron, with the deuteron being a sort of "nucleon" in its own right, where we combine $p(pn)=p(d)=|\frac{1}{2} \frac{1}{2}> |00>$, but I can't seem to reconcile that with the fact that there are still two identical nucleons (the protons) in a bound state, which sounds like it should violate Pauli exclusion for the same reason as before. What have I misunderstood?

dimwatt said:
What have I misunderstood?
Spin. The deuteron is a 3S1 state, which means the nucleons are both in the same spin state. In He3 on the other hand, the spins of the two protons are opposite.

## 1. What is the Pauli exclusion principle regarding nucleons?

The Pauli exclusion principle states that no two nucleons (protons or neutrons) can occupy the same quantum state simultaneously. This means that in an atom, each nucleon must have a unique combination of quantum numbers, including spin, orbital, and energy level.

## 2. How does the Pauli exclusion principle affect the stability of atoms?

The Pauli exclusion principle contributes to the stability of atoms by preventing nucleons from occupying the same state and thus avoiding repulsive forces between them. This allows atoms to maintain their shape and structure.

## 3. How does the Pauli exclusion principle relate to the periodic table of elements?

The Pauli exclusion principle plays a crucial role in determining the electron configuration of atoms and their placement in the periodic table. This principle dictates the maximum number of electrons allowed in each energy level and orbital, which directly affects an element's chemical properties.

## 4. Are there any exceptions to the Pauli exclusion principle?

While the Pauli exclusion principle holds true for most cases, there are a few exceptions, such as in heavy elements where relativistic effects come into play. These effects can cause the energy levels of electrons to overlap, allowing for more electrons to occupy the same state.

## 5. How does the Pauli exclusion principle impact nuclear reactions?

The Pauli exclusion principle plays a significant role in nuclear reactions by limiting the number of nucleons that can occupy the same state and determining which reactions are possible. This principle also helps to explain the stability of certain isotopes and the process of radioactive decay.

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