(a) Draw a schematic arrangement of Geiger- Marsden experiment showing the scattering of a-particles by a thin foil of gold. Why is it that most of the a-particles go right through the foil and only a small fraction gets scattered at large angles ?
Draw the trajectory of the a-particle in the coulomb . field of a nucleus. What is the significance of impact parameter and what information can be obtained regarding the size of the nucleus ?
(b) Estimate the distance of closest approach to the nucleus (Z = 80) if a 7.7 MeV a-particle before it comes’ momentarily to rest and reverses its direction. [Delhi 2015]
For most of the a-particles, impact parameter is large, hence they suffer very small repulsion due to nucleus and go right through the foil.
(b)K.E of the a-particle = potential energy possesed by beam at distance of closest approach.