The unit of radiation is not the photon, but it is the electron itself moving with the speed of light outside or inside nuclear range when it interacts momentarily with another electron bearing the same charge on atomic level or interacts constantly on nuclear level with one of two particles bearing the opposite positive charge. The positron forming with it gamma ray or a proton forming the neutron from which beta the speedy electron is emitted. In all these cases the electron moves with $c$ speed when the interaction between it and the other charged particle takes place at a distance equaling the basic nuclear diameter $r = 2.8 \times 10^{-15}\,\text{m}$. The speed of the electron $c$ on nuclear level is exceeded when the mentioned distance $r$ is shorter than its value, being for example the nuclear radius or shorter than its value, and this explains the energy of gamma exceeding $1.02\,\text{MeV}$ or beta exceeding $0.55\,\text{MeV}$. We are going to prove this fact about the speed of light through the universal unifying constant $U$ we came to some years ago.