Tuesday/ the milliSievert

In none of the reporting on television of the dangers of exposure to radiation from a nuclear power plant have I seen any explanation of how radiation is measured, and what levels of radiation would actually be dangerous.

So first things first.   Radiation dose equivalent exposure is measured in milliSivert (1 mSv = 10⁻³ Sv) or microSievert (1 μSv = 10⁻⁶ Sv).

Here are some examples of typical doses –

• Dental Radiography : 0.005 mSv
• Mammogram : 3 mSv
• Average dose to people living within 16km of Three Mile Island accident : 0.08 mSv; maximum dose: 1 mSv
• Approximated  radiation exposure at Fukushima Dai-Ichi Nuclear Power station within 20km: 0.023 mSv or 23μsv; 30km radius: 4μsv (on 03-16-2011 as per NHK World report – may change as this item is active)
• Immediately after the Chernobyl disaster, some 24,000 people living within 9 miles (15 km) of the plant – residents of nearby Pripyat – received an average dose of 450 mSv before they were evacuated.

In most countries the current maximum permissible dose to radiation workers is 20 mSv per year averaged over five years, with a maximum of 50 mSv in any one year.   A term that is used for nuclear workers is to aim for levels that are ‘As low as is reasonably achievable’, abbreviated as  ALARA.

This is not where the radiation story ends, though.    We are all bombarded with radiation from the environment, from food and from medical procedures (picture from World Nuclear Association’s website).    I get more of it when I fly (of course, airline pilots get even more), and I get radiated when I walk through the full-body scanner at airport security.    (The TSA admitted just today that a recent series of tests of these scanners produced levels 10 times higher than expected .. so they’re following up with more tests).