Atoms of the same element with different mass numbers are known as $\qquad$ .

According to the Rutherford's atomic model,the electrons inside the atom are

What is the percentage of $\alpha$-particles that have more than $1^o$ scattering in the Geiger-Marsden experiment (in $\%$)?

$A$ proton is fired from very far away towards a nucleus with charge $Q=120 \ e$,where $e$ is the electronic charge. It makes a closest approach of $10 \ fm$ to the nucleus. The de Broglie wavelength (in units of $fm$) of the proton at its start is: (take the proton mass,$m_0 = (5/3) \times 10^{-27} \ kg$,$h/e = 4.2 \times 10^{-15} \ J \cdot s/C$,$\frac{1}{4 \pi \varepsilon_0} = 9 \times 10^9 \ N \cdot m^2/C^2$,$1 \ fm = 10^{-15} \ m$)

Explain Rutherford's argument for scattered $\alpha$-particles.

Which scientist proposed the plum pudding model of the atom?