Hiroshima Porcelain Pieces Provide Insight Into Exposure Levels

Analyzing the neutron-induced fission tracks on certain objects found in Hiroshima enables scientists to calibrate the nuclear fluence. Geologist Robert L. Fleischer (Union College in New York), S. Fujita (Radiation Effects Research Institute in Japan), and M. Hoshi (Research Institute for Nuclear Medicine and Biology in Japan) have published their findings on a glass button found near ground zero in Hiroshima in the Health Physics Society Journal.

More recently, Union College geology student Jonathan MacDonald joined the team to determine the track density of fission tracks in porcelain fragments that were also found near ground zero. This study complements the previous work.

“At face value, these results are fluence values from a specific bomb event that will hopefully never be used again. These fission events occurred when thermal neutrons from the bomb caused fission in the normal trace amounts of uranium in the material,” MacDonald explained. “We determined the track density on the exterior glaze (glass), on the outside of one porcelain fragment and in a cross section of the glaze in another.”

While the value of the one sample nearly matches the previous estimates, the other one is 2 to 2.5 times higher. MacDonald will report the new values at the Geological Society of America’s North Eastern Section Meeting on March 25.

“If correct, the latter value may be important for regulation of human exposures in the U.S., because many of the current regulations are based on theoretical calculated values,” MacDonald said. “If this latter dose is correct—being higher than what is currently assumed—then the current standards should be less restrictive.”