EFFECT OF VALENCE NUCLEONS ON RMS CHARGE RADII AND SURFACE THICKNESS

The nucleonic promiscuity factor P = N(p)N(n)/(N(p) + N(n)), where N(p)(N(n)) is the number of valence protons (neutrons) or holes, is shown to be a useful and physically meaningful parameter in the description of RMS charge radii. The introduction of P in the radius formula R almost-equal-to R(c) + 0.07P/R(c) (R(c); droplet model 'closed-shell radius') reduces the x2/n' value by a factor of three. The empirically found mass number dependence of the P-dependent contribution to radii is in agreement with the qualitative theoretical expectation for the average strength of the isoscalar p-n interaction. A significant correlation between surface diffusity and promiscuity as well as between diffusity and radius is pointed out.