Expert: Expert - 8/27/2009

Question
Is there space between the protons and neutrons in the nucleolus? If so,and hypothetically if we could, what effect would changing the size of that space have.

Answer
> Is there space between the protons and neutrons in the nucleolus?

First a definition: protons and neutrons are collectively called "nucleons."

The question you ask (basically) gets down to two questions:
1) what is the size of a nucleon?
2) what is the distance between nucleons within the nucleus?

If the size of a nucleon is much smaller than the average distance between them, then we could say there is "space" between the nucleons. It would seem that it would be easy to measure both these quantities, and then we would know.

The problem arises that, when we look at very small things (like nucleons), quantum mechanical effects take over, and concepts like "size" become meaningless.

www.physlink.com/education/AskExperts/ae570.cfm

At these small sizes, we don't directly measure structure, we measure how much electrons are scattered in collisions with nucleons.

http://www.desy.de/f/hera/engl/chap1.html
http://prola.aps.org/abstract/PR/v103/i5/p1454_1

We can realiably state that the nucleus of an atom is about one fento-meter in diameter. We can also state that the "size" of a nucleon is about one-tenth that. The problem comes in that this is about as far as we can go. Hofstader's scattering measurments only told us the difference between a proton's electrical charge distribution and a point charge distribution. But does that mean the proton is actually that "size?" At these small sizes, charge distribution is all we can determine.

Within a nucleus, we can't determine if this charge distribution is altered by the strong force. So we can't tell if the "size" of a nucleon within a nucleus is larger, smaller, or the same size. Thus we can't determine if changing the distance between nucleons -- if such a concept has any meaning -- would make any difference.

Scientists have determined that certain numbers of nucleons within a nucleus are more stable than other numbers. We THINK this has something to do with some structure within a nucleus, but we haven't yet determined what that structure might be. The strong nuclear force disappears for objects further apart than a nucleus, so it's very hard to do any experiments with it.

We're still working on it. Perhaps some future scientists will develop an explanation for why some numbers are more stable than others.