You’re being exposed to radiation -- but it’s the amount that counts

Everyone is exposed to some radiation. It’s the level of exposure that determines whether there’s any harmful effect.

But how much radiation is a lot? Here are a few numbers for comparison.

(A microsievert is a unit that measures the biological effects of radiation.)

• Limit on whole-body exposure for a radiation worker for one year: 50,000 microsieverts
• One year’s worth of exposure to natural radiation from soil, cosmic rays and other sources: 3,000 microsieverts
• One chest X-ray: 100 microsieverts
• One dental X-ray: 40-150 microsieverts
• One mammogram: 700 microsieverts
• CT scan (abdomen): 8,000 microsieverts
• Full-body airport X-ray scanner: 0.0148 microsieverts
• Airplane flight from New York to Los Angeles: 30-40 microsieverts
• Smoking a pack a day for one year: 80,000 microsieverts
• Average dose to people living within 10 miles of 1979 Three Mile Island accident: 80 microsieverts
• Average radiation dose to evacuees from areas highly contaminated by the Chernobyl disaster: 33,000 microsieverts (Of 600,000 of the most-affected people, cancer risk went up by a few percentage points -- perhaps eventually representing an extra 4,000 fatal cancers on top of the 100,000 fatal cancers otherwise expected.)

Sources: TSA (APL report); CDC; FDA; NRC; ANS; IAEA; Wright State University in Dayton, Ohio