Even now, years after the Tohoku earthquake and tsunami, and the subsequent partial meltdown of the Fukushima reactors, we're still regularly asked "is it safe to go to Japan?"
In January 2015 we published a short, animated video that tried to put people's fears in perspective.
Taking the officially published level of background radiation in Tokyo at the beginning of 2015, how long would you have to stay before the radiation levels might make you suffer a significant increase in the chance of getting sick? (Not "get sick" but an increase in the chance you might.)
We took the internationally recognised standard, endorsed by every nuclear regulatory authority in the world, that 1 Sievert of radiation over a year increases the likelihood of developing cancer sometime in your lifetime by 5% (note: NOT that 5% of people WILL get cancer, but that everyone has the chance of developing cancer increased by 5% - some will, most won't.)
So, how long you'd have to be in Tokyo for the radiation levels to be a problem? Watch the video to find out.
It's overly simplistic! Yes, unashamedly we tried to simplify the matter. Rather than get lost in REMS Grays, and RADS we followed this guide as published in deepsenews.com.
No, and we don't claim to be, but we can read, and we read what the experts and official agencies are saying.
The United Nations body which is the world authority on understanding the health effects of radiation is the UNSCEAR - UN Scientific Committee on the Effects of Atomic Radiation.
On April 2, 2014 it published a report into the Fukushima disaster and said:
"The doses to the general public, both those incurred during the first year and estimated for their lifetimes, are generally low or very low. No discernible increased incidence of radiation-related health effects are expected among exposed members of the public or their descendants."
The study noted they DID find more cancers in their screening of residents, but said that was due to the high-level of screening they conducted.
"Increased rates of detection of [thyroid] nodules, cysts and cancers have been observed during the first round of screening; however, these are to be expected in view of the high detection efficiency [using modern high-efficiency ultrasonography]. Data from similar screening protocols in areas not affected by the accident imply that the apparent increased rates of detection among children in Fukushima Prefecture are unrelated to radiation exposure."
Well, maybe. That's certainly been the established position of health authorities since WWII, and the basis on which we produced our video.
But now there's growing evidence and argument from experts in radiology, that long-term exposure to low-levels of radiation may actually be beneficial to your health.
Which would explain why the residents of Ramsar in Iran, with a background radiation level of an astounding 250 mSv per year, have lower cancer rates than the world average.
If you want to read more on the debate about the efficacy of the Linear No Threshold Dose start with this paper from the National center for Biotechnology Information. Or read this 2013 piece scientist James Conca contributed to Forbes.com.
Radiation is a scary thing. You can't see it, you can't taste it, you can't feel it, but we all know exposure can cause cancer. So how much danger do we face from the crisis at Japan's Fukushima Daiichi nuclear power plant?
The Japanese government on April 12 2011 made a somewhat confusing statement regarding the plant. They said the situation was coming under control and there was very little risk of a catastrophic meltdown with large release of radioactive material. But, they lifted the crisis rating for the accident to 7, which is the highest level, and equal to Chernobyl, and widened the exclusion zone around the plant for fears of long-term health effects.
They said they expected the radiation in the current 20 km exclusion zone will reach the equivalent of 20 millisieverts a year, but this may extend to some areas as far as 30 km or more from the plant, depending on wind and water run-off.
We're all exposed to background radiation of an average 2.5 millisieverts a year.
This varies from place to place, and in one of the most naturally radioactive places on earth, Ramsar in Iran, the radioactive isotopes dissolved in the local hot springs raise the background level to 250 mSv a year (strangely, the residents are NOT all cancer-riddled).
A table from the World Nuclear Association (it's an international organisation that promotes nuclear power) indicates that 20 mSv a year is the current annual safe limit for nuclear workers.
The WNA says you have to reach exposure levels of 100 mSv a year (others say it's 50 mSv) before there's any evident increase in cancer.
So you'd have to spend a whole year within 20 kms of the Fukushima Daiichi plant to be exposed to the whole 20 mSv of radiation.
Time and distance is important when calculating the risk from radiation. The risk to your health increases the longer you are exposed, and the closer you are to the source.
Obviously if you're standing at the base of the broken reactor, without protection, you don't have very long before you start feeling ill. Stay in an affected area for less time, or get further away and the risk to your health drops rapidly.
Is Beijing a safe distance, or Honolulu, or London? Let's try somewhere a little closer to the action to see what affect you can expect - Tokyo.
On March 15th 2011 as uncontrolled releases of radiation emitted from the nuclear plant, and levels of 400 mSv an hour were being recorded at the reactor buildings, 240 km away in Tokyo there was panic as media reported levels of radiation 22 times higher than normal.
But what's normal for Tokyo? It's about 0.126 mSv, which means on that day, for a few hours, the background level of radiation was 2.5 mSv, equivalent to about half the dose you get from an abdominal x-ray.
And that was on the worst day of the crisis. Those levels were back close to normal by the next day, and remain pretty much so.
A month after the near meltdown a reading taken in Roppongi (Tokyo) on April 4th 2011 by the Japanese English language newspaper Metropolis, showed 0.176 mSv, marginally higher than the 'normal' of 0.126 mSv, and that was with the wind blowing from the north where the crippled reactors are.
Put some distance into the equation (remember radiation effects fall off with distance), and while increased levels of radiation may be detected in Canada, west coast USA and Europe, the experts insist they will be so small as to be insignificant with no effect on human health.
In 2013, two years after the meltdown, it was estimated that seawater containing 20 trillion becquerels of radioactive material had been released into the Pacific ocean. That includes the initial release of very radioactive water. Which brings us to now... let's just double that figure, and say 40 trillion becquerels.
Some scientists argue this is literally a drop in the ocean because the Pacific contains, naturally, the equivalent of 8,125,370,000 trillion becquerels of radioactive material.
This is a major point - strict food safety guidelines prohibit the sale of potentially contaminated foodstuffs. Produce is regularly and thoroughly tested. You can get results of weekly tests published on the website of the Ministry of Health Labour and Welfare.
Still, there are reports of fish being extracted from around Fukushima with high levels of contamination. This Reuters report in January 2014 noted the capture of Black Sea Bream with levels 124 times greater than the threshold for safe human consumption.
It's worth noting though, Black Sea Bream are currently restricted from being fished for human consumption - so no-one would eat one anyway.
We're not recommending a sightseeing trip to the gates of the Fukushima Daiichi plant, in fact you should heed the advice from the American, British and Australian governments and stay at least 20km from the place, but don't put off your travel plans. Pack your suitcases and get out there, a (no more dangerous than usual) world awaits you.
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