Summary
Highlights
When people refer to harmful radiation, they typically mean ionizing radiation, which has enough energy to strip electrons from atoms. This process can break chemical bonds and cause DNA mutations, increasing cancer risk. Cell phones do not use ionizing radiation; they use radio waves that are not energetic enough to damage cells.
Particle energy is measured in electronvolts (eVs), with typical radioactive particles having energies around one megaelectronvolt (MeV). The becquerel (Bq) measures the rate of nuclear decays in a source per second. The human body naturally and safely emits several thousand becquerels constantly. The curie (Ci) is an older unit for decay rates, equivalent to 37 billion becquerels.
The absorbed dose of radiation, or how much radiation your body absorbs, is measured in grays (Gy). One gray means one kilogram of matter has absorbed one joule of radiation energy. For example, a CT scan might expose someone to a few milligrays. The rad is an older unit equivalent to 0.01 gray.
The sievert (Sv) modifies the gray to account for the different health risks posed by various types of ionizing radiation, such as alpha, beta, and gamma particles. To convert grays to sieverts, you multiply the gray value by a radiation-specific factor (e.g., 20 for alpha particles due to their higher damage potential), making it a unit directly relevant to human health. An older equivalent is the rem, where one rem equals 0.01 sieverts.
Humans are constantly exposed to natural sources of radiation, typically a few millisieverts per year. Medical scans vary in their exposure, from less than 0.01 millisieverts for an X-ray to about ten millisieverts for a full abdomen CT scan. While radiation exposure carries risks, understanding these units helps in making informed decisions and puts everyday exposure into perspective, noting that it's a constant part of life.