Nuclear radiation is nothing to take lightly — just ask the three workers who were burned last week as they struggled to make emergency repairs inside the crippled Fukushima-Daiichi plant. A spent nuclear fuel pool, such as those at Fukushima, might give off some 3,000 millisieverts per hour of radiation, according to some experts. But it's worth remembering that just as it's the dose that makes the poison, how fast you consume any given dose matters too. As the ever-helpful Charlie Petit explains it:
"A dose is rate multiplied by time. Those figures at their high end are horrendous exposure rates. A few thousand millisieverts in a short period of time is a huge blow — if applied to the whole body it is enough to cause acute radiation sickness and, frequently, death. But 3000 millisieverts per hour is not a dose. It is a rate. A nanosecond of it is (I’d guess) trivial, five minutes of it are bad, an hour is to invite dreadful illness or even ugly death. It’s like a hose’s flow. Five gallons per minute is not one hefty bucket. It can be a thimbleful if you are real quick on the nozzle valve. It is a swimming pool’s worth if you stand there squirting it for quite awhile."
That's the idea efficiently depicted here in Alexandra Muresan's nuclear radiation chart. [Click to view larger]
What Muresan has done, quite ingeniously, is combine two graphs: one that shows dose as a function of time, and another comparing time and natural background radiation. Because they share a common axis — time — she's able to merge them into a single triangular visualization. Her trefoil design, of course, also happens to look a lot like the international symbol for nuclear radiation.
While there's really no starting point, per se, on the graphic, it's easiest to read by tracing each colored triangle in a clockwise direction. Since the right-hand axis is a dose (in millisieverts or mSV), and the bottom axis is time, dividing the former by the latter effectively gives you the rate of exposure (a rate is dose divided by time — the inverse of Petit’s operation). Keeping this rate in mind, follow the line over to the left-hand axis to see how it compares with the rate of natural background radiation.
Using this strategy to read the dark blue triangle, for example, and you’ll see that 2 millisieverts of radiation (right-hand axis) divided over the course of one year (bottom axis) corresponds to the "normal radiation rate" (left-hand axis). This amount sets the baseline, as humans can’t help but sop up some radiation if they insist on doing activities like breathing air, eating food, existing in this solar system.
Work your way down the right-hand axis, and you come to the dark orange triangle representing radiation levels recorded at Fukushima on March 15. Here, the dose is 400 millisieverts. The time span is 1 hour. This rate, according to the left-hand side of the triangle amounts to a whopping 1,752,000 times the normal background rate.
Bearing in mind that these levels were only detected for brief bursts of time, in air right above the reactors, and that in two towns near the Fukushima plant just one day later, authorities detected only 3.6 microsieverts of radiation, there’s broad consensus that Fukushima’s meltdown is severe, and could have continuing effects that we won’t appreciate for decades to come.
So what if, instead of in sudden blasts above overheating fuel rods, much smaller amounts of radiation are absorbed over many years? Clearly, the effects are much different, as you can glean by looking at the lighter orange triangle. Here, a dose of 350 - 400 millisieverts — a dose similar hour-long pulse at Fukushima — is spread out over some 70 years. Diluted by time, the radiation comes to just 3.5 times normal background exposure.
For sure, 3.5 times normal isn’t something to celebrate — it was high enough to set the bar for relocations after Chernobyl. At the same time, it is less than an average airline crew flying New York - to - Tokyo gets in a year (bright green triangle). And it’s far less than the lowest levels at which any increase of cancer is clearly evident (yellow).
So, while we all struggle to make sense of the disaster trifecta that has befallen Japan, Muresan lends the perspective of time and normalcy, giving us a better sense of what we should — and shouldn't — lose sleep over.
At Visualizing, we're gathering as many infographics, visualizations, and innovative renderings as we can to help shed light on Japan's ongoing crisis. Please upload your visualizations here, or send us a tweet at @VisualizingOrg.
We've also provided the following information and data resources to get you started:
- The Risk Science Blog: The Fukushima nuclear reactor disaster and its implications to public health
- MIT Nuclear Science Information Hub: Introduction to Radiation Health Effects and Radiation Status at Fukushima
- Nature News Anatomy of a Meltdown
- Idaho State University’s Radiation Information Network
- Canadian Center for Occupational Health and Safety Information on Ionizing Radiation
- US Nuclear Regulatory Commission Fact Sheet on the Biological Effects of Radiation
- Wikipedia on Radiation Poisoning