Claim: The amount of repulsion varies from nucleus to nucleus, where the total repulsion can be expressed in four parameters which are known as the Racah parameters.
Evidence: The amount of repulsion varies from atom to atom, depending upon the number and spin of the electrons and the orbitals they occupy. 
The total repulsion can be expressed in terms of three parameters A, B and C which are known as the Racah parameters after Giulio Racah, who first described them.