text: The first estimate of a nuclear charge radius was made by Hans Geiger and Ernest Marsden in 1909, under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester, UK. The famous experiment involved the scattering of α-particles by gold foil, with some of the particles being scattered through angles of more than 90°, that is coming back to the same side of the foil as the α-source. Rutherford put an upper limit on the radius of the gold nucleus of 34 femtometres.
  Later studies found an empirical relation between the charge radius and the mass number, A, for heavier nuclei (A > 20):
  :R ≈ rA
  where the empirical constant r of 1.2–1.5 fm can be interpreted as the Compton wavelength of the proton. This gives a charge radius for the gold nucleus (A = 197) of about 7.69 fm.