**Question 3. The bouncing neutron**

*I don't understand what's meant by a neutron bouncing on a table that you mention in the short film, could you explain this in more detail?*Irene.

Hi Irene,

Neutrons that are moving slowly enough are reflected from most surfaces. This reflection is due to the strong nuclear force and the wave-like nature of the neutron, and is similar to the total internal reflection of light at the interface between glass and air. There is a critical speed for the neutron, which depends on the material; for most materials this is about 5m/s. As long as its speed is slower than this critical speed, the neutron wave undergoes total reflection at the surface. An upper speed of 5m/s corresponds to dropping the neutron from a height less than 1.3m. So if the neutron is dropped onto a table from any height smaller than this it will bounce. There is no loss of energy at the surface and so the bounce is perfect. As it bounces, the neutron is moving in the gravitational potential of the Earth and has a set of discrete energies which we find by solving the Schrodinger equation. These discrete energies correspond to discrete frequencies which, roughly speaking, are the allowed oscillation frequencies of the neutron wave. For example, the lowest allowed frequency for the neutron in the Earth's gravity is 337Hz.

Mike