Photo/IllutrationWorkers decontaminate land in Date, Fukushima Prefecture, in 2013. (Asahi Shimbun file photo)

A nuclear physicist who has drawn attention for tweeting about fallout from the Fukushima nuclear disaster has admitted that he and a colleague underestimated radiation doses in an article for an international scientific journal.

Ryugo Hayano, professor emeritus at the University of Tokyo, said the error, which he recognized on Jan. 8, was “unintentional.”

The article, carried in the Journal of Radiological Protection’s online edition in July 2017, listed average radiation doses that were one-third of the actual levels for people in Date, a city around 60 kilometers northwest of the crippled Fukushima No. 1 nuclear plant, he said.

Hayano’s admission came after an atomic nucleus expert submitted a letter to the editor of the journal last year to point out unnatural data carried in the report.

The radiation doses in the article were based on dosimeters worn by Date residents after the nuclear accident unfolded in March 2011.

“Even if residents lived in the most contaminated area of Date for 70 years, the median of the doses would not exceed 18 millisieverts,” the article concluded.

However, Shinichi Kurokawa, professor emeritus with the High Energy Accelerator Research Organization, an institute jointly used by national universities, raised doubts about the data presented in some sections of the report.

When Hayano and his colleague re-examined the figures, they found that they mistook a monthly dose recorded on a dosimeter as the figure for three months of exposure.

“Even after the error was fixed, I believe the annual doses will be within the 1-millisievert mark,” Hayano said.

The benchmark upper limit for radiation exposure among ordinary people is 1 millisievert a year.

Hayano has frequently tweeted about radiation levels and doses from the nuclear disaster.

He was also involved in another research paper that analyzed radiation doses among people in Date. Kurokawa also questioned the veracity of a chart in the second report.

The second report has often been cited in discussions by the government’s Radiation Council on setting standards for protecting people from radiation.

The two research papers were produced after the Date city government provided Hayano’s research team with data on radiation doses of about 59,000 residents.

But it has emerged that data for 27,000 citizens were provided without their consent.

The city plans to set up an investigation panel to find out why it occurred.

Date has a population of 61,000.

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CORRECTION

This article was corrected on Feb. 16, 2019.

The quote in the ninth paragraph attributed to Ryugo Hayano was a mistake.

The ninth paragraph originally read: "Even after the error was fixed, I believe the average of annual doses will be within the 1-millisievert mark," Hayano said.