# Classical radius of nucleons and quarks

#### relativityfan

hi,

how do you calculate the classical radius of nucleons or quarks? do you include only the electrostatic potential energy or also some nuclear potential energy?. i have read many times that the classical radius of nucleons is lower than the classical radius of the electron, is it right?

#### Meir Achuz

Homework Helper
Gold Member
The "classical radius", usually defined as e^2//mc^2, has no physical significance.
It would be much smaller for a nucleon than an electron, but the physical radius of a
nucleon is almost 1 fm, while the electron physical radius is probably 0.

#### tom.stoer

For nucleons one can measure form factors (and structure functions); form factors are something like the Fourier transform of the corresponding density (charge, current, ...) so one can measure the radius indirectly via the charge, current, ... distributions

#### relativityfan

The "classical radius", usually defined as e^2//mc^2, has no physical significance.
It would be much smaller for a nucleon than an electron, but the physical radius of a
nucleon is almost 1 fm, while the electron physical radius is probably 0.
thank you, and how does it compare with the photon?

#### Meir Achuz

Homework Helper
Gold Member
A photon is considered a point particle.

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving