In a nuclear reactor heavy nuclei is not used as moderators because

The period of revolution of an electron revolving in nth orbit of $$\mathrm{H}$$-atom is proportional to

Angular momentum of an electron in hydrogen atom is $$\frac{3 h}{2 \pi}$$ ($$h$$ is the Planck's constant). The KE of the electron is

A beam of fast moving alpha particles were directed towards a thin film of gold. The parts $$A, B$$ and $$C$$ of the transmitted and reflected beams corresponding to the incident parts $$A, B$$ and $$C$$ of the beam are shown in the adjoining diagram. The number of alpha particles in