The distance between protons inside an atomic nucleus varies depending on the element and the isotope of the atom. In general, protons in the nucleus are extremely close together compared to their size.
The size of a proton is typically measured in femtometers (1 femtometer = 10^(-15) meters). The approximate size of a proton is about 0.8 to 0.9 femtometers. However, the actual distance between protons within a nucleus can be smaller than the size of an individual proton.
The nucleus of an atom is held together by the strong nuclear force, which is one of the fundamental forces of nature. This force overcomes the electrostatic repulsion between protons due to their positive charges. The strong nuclear force acts over a very short range, typically only a few femtometers.
In larger nuclei, the protons are tightly packed together, and the distance between them can be on the order of a few femtometers. However, as the number of protons increases, the electrostatic repulsion between them becomes stronger, requiring more neutrons to stabilize the nucleus.
It's important to note that the density and arrangement of protons within a nucleus are complex, and the specific distances between individual protons can vary. The concept of a fixed distance between protons is an approximation to describe the overall structure and behavior of atomic nuclei.