Simplify the following text for a Grade 8 native English-speaking person.
Original: The diameter of the nucleus is in the range of for hydrogen ( the diameter of a single proton ) to about for the heaviest atoms , such as uranium .
Simplified: The size ( diameter ) of the nucleus is between 1.6 fm ( 10-15 m ) ( for a proton in light hydrogen ) to about 15 fm ( for the heaviest atoms , such as uranium ) .