I usually really enjoy the New Scientist, and I’ve had a warm spot for them since they interviewed me back in 2005. Fun magazine, but they sometimes let their enthusiasms get in the way. (If you followed Climategate, you may recall that a poorly-sourced story became the basis for the since-debunked IPCC conclusion that glaciers in the Himalayas would be gone by 2035.)
Well, they’ve managed to step in it again; I could wish they were a little better with editing and fact-checking. Today, in a story headlined “Fukushima radioactive fallout nears Chernobyl levels” they then reported that the Cesium-137 and Iodine-131 relase from Fukushima had reached as much as 73 percent of what was released into the atmosphere by Chernobyl.
Considering what Chernobyl did, this seemed unlikely. So, let’s check their arithmetic.
First of all, just looking at their numbers, they say there’ve been about 1.2-1.3×1017 Becquerel (Bq) of I-131 released per day in the first two days after the accident. That’s from the Comprehensive Test Ban Treaty Organization, and the number has been reported a couple of times; it should be reasonably accurate.
A “Becquerel”, by the way, is a measure of radioactivity corresponding to one radioactive disintegration per second. By comparison, a banana has about 20 Bq in the form of Potassium-40. So the I-131 release here is about a quadrillion bananas, which is pretty significant.
By comparison, they say, Chernobyl released about 1.7×1018 Bq of I-131 in the ten days following the accident. If you just do the division, that’s (1.2/1.7) and the order of magnitude divides out — sure enough, that’s about 0.68.
On the other hand, Fukushima is largely releasing the volatile stuff only, And certainly the New Scientist article does say, in the second paragraph:
The difference between this accident and Chernobyl, they say, is that at Chernobyl a huge fire released large amounts of many radioactive materials, including fuel particles, in smoke. At Fukushima Daiichi, only the volatile elements, such as iodine and caesium, [sic — the international spelling] are bubbling off the damaged fuel.
That difference is pretty significant, though — because some estimates have the total radioactivity release from Charnobyl as high as 3.3×1020 Bq. That’s roughly 2000 times as much total.
I presume, however, that “Fukushima release approaching 0.0005 times as much radioactivity as Chernobyl” wouldn’t make near as good a headline.
(Homework problem: assume there is one atom of I-131 left from the Chernobyl accident. The half life of I-131 is 8.2 days, or about 193 hours. How many atoms of I-131 did there have to be at the time of Chernobyl to leave that one atom now.)