Transcript

JIM AL-KHALILI

I'm in Japan four months after the tsunami struck the plant. What remains of the radiation now, and does it justify the exclusion zone?

This is the village of Iitate, population usually 6,165. But it's been completely evacuated, even though it's outside the exclusion zone. That's because radioactive particles from the Fukushima reactor have been carried here by the weather. Now it's entirely abandoned-- every house, every street, even this school.

I've come here today to witness something I've never seen before. In fact, it's an event that's only happened a few times during my lifetime. And that's part of a radioactive cleanup operation. And so as a precautionary measure, I'm wearing these Wellington boots just to make sure that I don't get any contamination from any dust on the ground as I walk around.

JIM AL-KHALILI (VOICEOVER)

Today, scientists from Fukushima University will take measurements of the soil, which is where most or all of the radioactive particles will be now, because they've fallen from the air to the ground. They're looking for two toxic elements which escaped from Fukushima - in particular, radioactive iodine and radioactive cesium.

But one of these elements - radioactive iodine - is only present for a short time.

HITOSHI KANAZAWA (VIA TRANSLATOR)

Right now, because about four months has passed, I predict the iodine has disappeared.

JIM AL-KHALILI

And that's because radioactive elements decay over time, eventually changing into stable, non-radioactive forms. It's the half life of an element that's a good measure of how quickly this happens.

HITOSHI KANAZAWA (VIA TRANSLATOR)

So only traces of caesium 137 and 134 are being detected.

JIM AL-KHALILI

So there will only be caesium in the soil. How dangerous is this? How long will it remain in the ground?

HITOSHI KANAZAWA

The half life of caesium is said to be close to 30 years. So for a long time, caesium will be the biggest problem.

JIM AL-KHALILI

Back in the lab, they found high levels of radiation in the top 2 and 1/2 centimetres of the soil. Other studies from nearby found levels more than 500 times higher than normal.

Removing this topsoil here will be an expensive option. And Iitate isn't even in the exclusion zone. Recently, the Japanese government has been monitoring the radiation level across 50 sites inside the zone. They've set their safety limit at 20 millisieverts per year, which is the same limit as for people working in the nuclear industry in the UK. And what they've found is that 35 of the sites exceeded this level, and the highest reading was 500 millisieverts.

The tests will help decide whether these people can go home. The government has decided to keep the exclusion zone in place. But that's a more complex decision than it looks.

For perspective, you'd get around that level - 20 millisieverts a year - from two CT scans per year. On one hand, setting such a limit protects people's health effectively. But on the other, that comes at a cost - the upheaval of 78,000 lives.