When an alpha particle is emitted from the nucleus of an atom?

During an alpha decay

Explanation:

An alpha particle is a particle consisting of 2 protons and 2 neutrons - basically it is equivalent to a nucleus of helium.

Alpha particles are emitted during alpha decays, which are one of the three types of radioactive decays (the other two being beta decay and gamma decay) in which an unstable nucleus decays emitting an alpha particle:

In the process, the original nucleus X loses 2 protons and 2 neutrons, so:

- its atomic number decreases by 2 units: Z --> Z-2

- its mass number decreases by 4 units: A --> A-4

waves moving from a fast medium to a slow medium will experience a reflection as light travels more slowly than red light. total internal reflection occurs when the critical angle is.