The radius of the nucleus is related to the mass number $A$ by

Rutherford's $\alpha$-particle scattering experiment is related to the size of the ..........

Write down the results of the cathode ray discharge tube experiment.

Fill in the blanks:
$(i)$ For the discovery of neutrons,$\alpha$-particles were bombarded on a thin sheet of ......... .
$(ii)$ For the $\alpha$-particle scattering experiment,Rutherford used a gold foil of thickness ......... .
$(iii)$ The radius of an atom is approximately ......... and the radius of the nucleus is ......... .
$(iv)$ The entire positive charge of an atom is concentrated in a very small region,which is called ......... .

The penetration power of a proton is:

What is the ratio of the mass of a proton to the mass of an electron?