Atoms can undergo processes that result in

• [[$\alpha$]] radiation, which gives out helium-4 nucleii (which are bundles of two protons and two neutrons)
• [[$\beta^-$]] radiation, which gives out an electron and an antineutrino (the antiparticle of a neutrino)
• [[$\beta^+$]] radiation, which gives out a positron (antiparticle of an electron) and a neutrino
• [[$\gamma$]] radiation, which gives out photons (particles of electromagnetic radiation) of high energy

Fun fact: if a particle (like an electron) meets up with its antiparticle (a positron), both particles get annihilated, resulting in energy
[[$$E = 2mc^2$$]]
In the case of an electron and a positron, the energy released by this annihilation is of around [[$8\cdot 10^{-14}$]]. So, a gram of electrons and positrons being annihilated equals [[$4\cdot 10^{26}$]] joules of instant energy.

The amount of atoms [[$\Delta N$]] undergoing nuclear reactions in a unit of time [[$\Delta t$]] is proportional to the amount [[$N$]] of atoms that have not reacted yet. Mathematically:
[[$$\frac{\Delta N}{\Delta t} = -\lambda N$$]]
for a constant [[$\lambda$]].