Unless you've been living in a bizarre time warp or have encased your head in concrete / attempted a home lobotomy, you can't have failed to notice that Japan is in the middle of a humanitarian crisis after a magnitude 8.9 earthquake and the resultant tsunami. The sheer scale of the damage done is unreal, and the human displacement staggering. Sadly, the death toll continues to rise. In the midst of all this chaos, the spectre of a nuclear accident has almost overshadowed the frankly immense natural disaster. A few people have asked me to explain the biological impact of Fukushima and radiation in general - I'll try to avoid a technical digression onto the design and just stick to the medical physics, given that's my limited sphere of knowledge. So here is the idiot's guide to radiation. I have included a few on my own humble thoughts on nuclear power at the end and links to how you can donate to Japan at the end of the post.
What exactly is radiation ?
Radiation refers to any energetic particle or waves which travel through a medium / space. Generally 'radiation' refers to what is called ionizing radiation - particles or waves with enough energy to knock electrons out of atoms / molecules. Ionizing forms include X-ray, Gamma rays, and Alpha articles. Radiation can also refer to non-ionizing forms of radiation, like radio waves, microwaves and visible light. The concept that visible light is a form of radiation strikes some people as strange given the often times negative associations of the word radiation but it is utterly true to say. Radiation is all around us all the time and has been since the dawn of humanity.
|Good God! Radiation EVERYWHERE!!|
Why can Ionizing radiation become a problem?
Ionizing radiation can remove electrons from atoms / molecules. So why is this a bad thing ? Aren't there loads of electrons just floating around anyway? Well yes, so I'll explain. And here, to paraphrase L'Oreal adverts of yesteryear, comes to science. When an atom / molecule is stripped of an electron, they become electrically unpaired and free to float around. As a result, they are highly chemically reactive. We call these particles free radicals. Free radicals tend to react everywhere and just love messing about in biological tissue, reacting with whatever organic material happens to be around. The end result can be cancer. So free radicals are not exactly ideal to have running about in biological tissue.
|The New Radicals, however, are just fine for biological tissue. You get what you give.|
How is radiation dose measured?
Put as simply as possible, the damage from ionizing radiation is directly related to the energy absorbed. Energy is measured in units called Joules (J) and mass is measured in the kilograms (kg). The gray (Gy) is a quick way to express the energy per kilogram (J/kg) deposited into any material but it only tells part of the story when you consider humans; Different biological tissue responds differently to radiation and indeed to different types of radiation. To quantify this, we have to use weighing factors for both the type of tissue AND the type of radiation to calculate the absorbed dose. This new measurement we call the sievert (Sv) and it is the unit most often discussed when we talk about the effects of radiation on human tissue. In practive, the sievert is a big unit, we often times we use the microsievert (1 uSv = 0.000001 Sv) or the millisievert ( 1 mSv = 0.001 Sv). Pretty much everything we do results in some radiation exposure. Even eating a single banana results in a dose of 0.1 uSv. This is sometimes referred to, semi tongue in cheek, as BED: the banana equivalent dose. But don't let this radioactivity put you off delicious bananas - all food has some radioactivity. Over a year, you'll imbue over 0.4 mSv naturally occurring radiation from food. Obviously this isn't so bad, but it raises the question - what is bad ?
|This banana's minuscule radioactivity has not damned his enthusiasm for cheer leading|
What are the limits ?
So what exactly is the 'safe' radiation level and when does exposure become detrimental ? Well, stolen from the excellent BBC article (they even interview a medical physicist, sometimes my faith in journalism is rewarded!) here are some typical levels.All thanks to BBC for the graphic...
|Stealing from the BBC is not only fun, it's informative!|
|The newly introduced Ionizing radiation warning symbol. Subtle.|