Sunday 28 August 2011

Radiation (2)

Where was I? Previously I worked out that my exposure to radiation in the air over the five months to 20 August may be 1.19 mSv, or 2.1 mSv for the year up to 11 March 2012. But that's not the whole story. I have to add in internal radiation (what I breathe in or take in from food), and radiation from medical and other sources. Today I'll look at the latter.

If you do a search for 'Radiation Calculation' you'll find all sorts of American sites which are a lot of fun - add 1 millirem if you sleep with someone, 1 millirem if you use a computer or watch TV -  but the US works in rems and millirems (10 millirems to 1 microsievert). This is really too complicated. I can't cope with that so I'm going to stick to Japanese and European sources and the sievert.

Radiation in Japan from medical sources is said to be three times the world average (lots of scans). However, my tally since March is zero (haven't had time even to go to the dentist) but I'd better add in some for the total to next March. I'll be having a chest X-ray in the company medical in October, so that's 0.1  mSv. Koriyama City has sent me a coupon for a free mammogram - 2 mSv, a very high figure, and let's add 0.03 mSv for a dental X-ray. So that's 2.13 mSv for medical, bringing the total so far to  4.23 mSv for the year to 11 March 2012.

Done quite a bit of flying in my life. Visited the UK in May and July. The National Institute of Radiological Sciences (Japan) has a thing called a JISCARD where you select the year and month you travelled and it will calculate the cosmic radiation you received: 49 μSv to London and 46 μSv for the return journey. Let's multiply that by three to include a planned trip at Christmas. Total  0.285 mSv. (BTW a friend whose husband is a pilot tells me the staff are constantly monitored.) So that ups my estimated total exposure in the year to 11 March 2012 to  4.515 mSv/year.

I've taken another look at that figure for a mammogram. NHS Direct (the UK government website) gives a figure of 2 to 5 mSv with the usual explanations about the background radiation we live with all the time and the risk of getting breast cancer outweighing the risk of the test. I'm sure that's right under normal circumstances. It's hard for an amateur to know what figures to use and I'm sure there are lots of different kinds of mammograms. My coupon is valid until the end of January next year. I'm going to have to look into this. Maybe I'll go and visit City Hall (which issued the ticket) and see what they have to say.

Next time, the trickier question of internal radiation. The big one.

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