High concentrations of radioactive tellurium and silver have been found in soil around the Fukushima No. 1 nuclear power plant, according to the science ministry's contamination maps released on Oct. 31.
High concentrations of radioactive tellurium and silver have been found in soil around the Fukushima No. 1 nuclear power plant, according to the science ministry's contamination maps released on Oct. 31.
The elements, minor components of radioactive fallout, were detected at sampling locations within 30 kilometers of the stricken nuclear plant.
An analysis showed that the concentration levels equaled a 50-year human radiation exposure of up to 3.2 millisieverts, the ministry said.
Soil samples were collected at about 2,200 locations within 100 km of the plant between June 6 and July 8. Studies were conducted on the concentrations of about 800 samples of tellurium-129m and about 350 samples of silver-110m.
"We have confirmed that the contributions of tellurium and silver to radiation doses are small compared to that of cesium," a ministry official said. "Neither tellurium nor silver easily accumulates in human bodies."
The symbol "m" indicates that the nuclides in question differ in properties from tellurium-129 and silver-110.
Tellurium-129m, with a half-life of about 34 days, is generated by nuclear fission of uranium fuel. When accumulated in human bones, tellurium-129m is excreted from the body in a shorter time than iodine-131, a major component of radioactive fallout along with cesium-134 and cesium-137.
A peak tellurium-129m concentration of about 2,660,000 becquerels per square meter was detected about 2.5 km from the nuclear plant in the town of Okuma.
Silver-110m, with a half-life of about 250 days, tends to stick to hemocyanin, or blood pigment in squid and other animals. A peak silver-110m concentration of about 83,000 becquerels per square meter was found about 5 km from the nuclear plant in the town of Futaba.
Both locations lie in the no-entry zone within a 20-km radius of the nuclear plant.
The ministry estimated that a person who stays at these locations for 50 years would receive a combined internal and external radiation dose of 0.6 millisievert for tellurium-129m and 3.2 millisieverts for silver-110m.
Calculations for 50 sample locations showed that tellurium and silver combined accounted for less than 1 percent of the total radiation exposure, and cesium accounted for most of the rest, according to ministry officials.