Here’s a short overview of the three types of radioactive emissions:

Alpha:

• Helium nucleus (two protons and two neutrons)
• Mass: 4 atomic mass units, charge: +2, ~5% light speed
• Emitted when a nucleus is too big and unstable (result is more tightly bound and has lower energy), e.g. Uranium 238 and Radium 226
• Most ionizing
  • Therefore, highly dangerous.
  • However, the particle is large and loses energy rapidly, resulting in it being very short range and easily blocked by layers like skin or paper. Only dangerous if inhaled or ingested.
• Smoke alarms

Beta:

• High energy electron or positron
• Mass: tiny, charge -1, ~99% light speed
• Emitted when a nucleus has too many neutrons (e.g. Nitrogen 14), it turns one into proton
• Less ionizing
  • Loses energy slower: higher range, harder to stop.
  • About 2cm through living tissue, 3mm aluminium
• Thickness detectors for QA of thin materials (like paper), tracers (PET scan)

Gamma:

• Photon
• Mass: 0, charge: 0, 100% light speed.
• Emitted when a nucleus has too much energy
• Tens of cm through living tissue, halved in intensity by 1.2cm lead
• Least ionizing, but most harmful by exposure (due to high penetration)
• Medical imaging (PET scan: after beta positrons collide with body electrons, gamma is emitted and detected)