There are many units used to measure radiation. I will be using the units called micro-Seiverts (which is techno-geek for 1 millionth of a Seivert and is abbreviated “uSv“). The unit is written with a greek letter “mu” (which translates to the letter “m”). Since there is no Greek on my keyboard I’m going to use the letter “u”, which sort of looks like “mu”. Why don’t I use an actual “m”? Because that actually stands for milli-Seivert. A milli-Seivert is one thousandth of a Seivert or 1000 micro-Seiverts.
Sorry, if some of you know all this already. I’m writing this for aircrew and frequent flyers, and most don’t know this stuff. So let me explain it a little…
A Seivert is a unit of radiation used to measure the absorption of radiation in human flesh. Seems apt. And it’s popular in this moment of time. Also, my gamma ray detector uses the Seivert (Sv). So I’m going to use it.
The chart below can be found on Wikipedia. Click on it and you’ll go to the full, zoomed view. It’s a great way to compare radiation exposure from everything from bananas to Fukijima. What I’d like you to notice, though, is that it shows the NORMAL YEARLY BACKGROUND DOSE as 4,000 uSv. This is the baseline that I’m going to use. In the short time I’ve been using my radiation detector, I’ve noticed that ground levels of radiation in North Carolina (.09 uSV) and also Dallas, Texas (.06uSv), are extremely low…almost zero. I’m going to set my radiation detector up so that it will go orange if levels will cause the cumulative dose to go above 4000 uSv per year.
Radiation exposure is cumulative! Apparently the body doesn’t recover from being hit by gamma rays. They add up over a lifetime. You could take 4 million bullets and throw them (not shoot) at someone and it’s not going to add up to one bullet shot at a velocity of 1200 ft per second. But you can throw radiation at a person and when it reaches 4 million micro-Seiverts the person will likely die. Radiation is cumulative. If you get a heavy dose one year, it’s best to get that time back another year, by staying in low radiation areas.
And this is where my concern for fellow aviators comes into play. We fly at high altitude for many hours year after year. Obviously we aren’t getting lethal doses or we’d all die. But does it have lesser affects on us that we only notice when we start getting on in years? Well, before we get into the health effects, let’s get some actual numbers.