A straightforward theory of $\alpha$-particle scattering from a thin metal foil is based on the four assumptions listed below. Which assumption is exact and is not an approximation?
- AEach $\alpha$-particle interacts with just one nucleus.
- BThe $\alpha$-particles lose no kinetic energy when they are deflected.
- CThe metal nuclei do not recoil.
- DTotal momentum is conserved.