Types of radiation

• Alpha rays (α): Alpha rays are streams of positively charged particles made up of two neutrons and two protons (helium nucleus). In the natural world, alpha rays are given off by radium 226. In air, the particles cannot travel more than a few centimeters.
• Beta rays (β): Beta rays are streams of electrons. In air, the particles can travel several dozen centimeters in a zigzag pattern.
• Gamma rays (γ): Gamma rays, the most penetrating type of radiation, are electromagnetic waves. They can pass through the human body. X-rays that are used in X-ray machines are also electromagnetic waves.

Radiation units

• Becquerel (Bq): The becquerel (Bq) is the unit of radioactivity. The radioactivity of a substance measured in becquerels is the number of its nuclei that decay each second.
• Gray (Gy) and Sievert (Sv): These units express the effect of radiation. The gray expresses the amount of radioactive energy received, while the sievert expresses the effect on a human being. Normally the gray and the sievert are used to express quantities per hour; the units are Gy/h and Sv/h, respectively.