Safe radiation dose

What is a safe radiation dose? The best answer is “It depends”. Though some puritans may argue that there is no safe dose!

There is no universally acceptable safe dose. For radiation workers, Atomic Energy Regulatory Board (AERB) wants the annual dose to be “as low as reasonably achievable” (ALARA); also it should not exceed 30 millisievert (mSv) excluding the dose due to natural background radiation and medical exposure, if any. AERB dose limit at 30mSv is lower than 50 mSv prescribed by USA (Sv is a unit of biologically effective dose. One Sv corresponds to a radiation energy absorption of one joule per kg; millisievert is one thousandth of a Sv). I have received about 0.9mSv while recovering a lost radiation source used in industry.

During the Fukushima accident one worker received 106mSv. Dose to recovery workers are not published so far.

For members of the public, the dose limit is one mSv. Pregnant workers may continue to work but the dose to the foetus should not exceed one mSv. In medically justified procedures the following doses in mSv may be considered as safe. Cardiac CT scan 12; angioplasty (a life-saving procedure involving removal of blocks in blood vessels)on an average 400; at times even 1000mSv; treatment of hyperthyroidism, 100,000; radiation treatment of cancer 60,000 mSv to part of the body. In all cases doses must be ALARA without losing medical benefits.

 In USA, the dose limit for an astronaut is 250mSv per mission. In an off-site radiation emergency, sheltering and administration of stable iodine may start at a minimum dose of 20 mSv; evacuation is mandated at 100mSv.

The average natural background radiation dose is 2.4mSv annually. In England & Wales, residents of over 100,000 to 200,000 homes are exposed to more than 10mSv annually from radon, a radioactive gas found in nature. The maximum value is more than 100mSv. Millions of persons in countries with temperate weather receive doses ranging from 5 to10 mSv from radon decay products

Thus, we accept different values of doses as safe and acceptable, depending on circumstances. One need not lose sleep over receiving a few tens of mSv, if the occasion demands it.