millisievert

But 20 millisieverts a year is at the top of an internationally set range for safety in long-term-exposure situations.

Radiation of up to 49 millisieverts per hour was detected inside the building on April 17 when the company sent in a robot.

At the time of the workers' withdrawal, some part or parts of the plant were emitting 10 millisieverts (mSv) of radiation per hour.

Background radiation delivers the average person a radiation dose of about 3 millisieverts (mSv) a year.

A level of 1, 000 millisieverts per hour is four times the level emergency work crews at the site are allowed to experience in a full year.

To put that in perspective, in the United States, a person typically gets a radiation dose of 6. 2 millisieverts per year.

But as an emergency measure, the ministry of health on Tuesday raised that to an accumulated 250 millisieverts.

Exposure to over 100 millisieverts a year is a level which can lead to cancer, according to the World Nuclear Association.

The limit for occupational radiation exposure among workers who deal with radioactive material is 50 millisieverts.

But there is no hard evidence proving that low dose radiation, below 100 millisieverts, is likely to cause cancer.

But in general, in an emergency situation, keeping it below 500 millisieverts is pretty safe, said Nolan E.

The average dose for a nuclear plant worker is 50 millisieverts over five years.

Radiation levels of 400 millisieverts per hour were recorded within the site on Tuesday.

Japan's health ministry set the radiation exposure limit for workers at the plan at 250 millisieverts in March.

Levels of 400 millisieverts per hour had been recorded near the No 4 reactor, the government said.

A spike in radiation levels near the reactors on Tuesday ranged from 30 to 400 millisieverts.

Radiation levels at the plant Tuesday were between 100 and 400 millisieverts per hour, Japan's Chief Cabinet Secretary Yukio Edano said.

Doses of 1, 000 millisieverts per hour were detected in the water, Tepco and nuclear safety officials said.

The average exposure amount for the month was 3. 1 millisieverts.

Exposure to 1, 000 millisieverts (1 Sievert) of radiation can cause radiation sickness.

A full-body CT scan gives a radiation dose of 20-30 millisieverts.

The highest reading was 508 millisieverts in the town of Okuma, about 3 km from the nuclear plant.

A single dose of 1, 000 millisieverts -- or one sievert -- causes temporary radiation sickness such as nausea and vomiting.

That's a huge dose when you consider that each year we receive an average of 2. 4 millisieverts from natural sources such as radon.

Still, exposure for emergency workers in Japan is currently capped at 250 millisieverts of radiation annually.

Nakagawa said that normally nuclear power plant workers in Japan are limited to accumulated radiation doses of 100 millisieverts.

In Japan, prior to the disaster, the average exposure was 1. 5 millisieverts, according to the Japanese government.