Ground zero. Researchers have reconstructed neutron doses from irradiated materials at Hiroshima.

Big Blowup Over Radiation Study

TOKYO--A new analysis of the radiation delivered by the atomic bomb dropped on Hiroshima has created some bitter fallout. The work, published last week in Nature (31 July, p. 539), helps resolve long-standing uncertainties over the estimated doses of neutron radiation. But the publication doesn't mention that the work was part of a pending broader international study, leaving other contributors fuming.

Dosimetry measurements from the Hiroshima and Nagasaki bombs are combined with human epidemiological data and used to create radiation-protection guidelines. A big snag is that measurements of high-energy "fast" neutron radiation shortly after the 1945 bombings provided data only up to 700 meters from ground zero, leaving researchers to make inferences for greater distances. A group led by radiobiologist Tore Straume of the University of Utah School of Medicine in Salt Lake City provided a direct indication of fast-neutron exposure by developing methods to measure the conversion of copper atoms to an isotope of nickel (63Ni) by fast neutrons. The work is part of an overarching study, called Dosimetry System of 2002 (DSO2), that draws upon a wealth of measurements to clear up discrepancies in a previous study completed in 1986.

The Straume group's letter claims that its nickel isotope measurements confirm earlier estimates of fast-neutron exposure. But neither the paper nor a commentary by Mark Little, an epidemiologist at the Imperial College Faculty of Medicine in London, mentions the DS02 effort, which is incorporating revisions in the bomb's estimated yield, detonation height, and ground zero; recalculating the shielding provided by terrain and tall buildings; and analyzing various materials retrieved from the rubble for clues to the radiation they received. "This undermines a very excellent cooperative relationship between American and Japanese scientists," says Robert Young, a radiobiologist who heads the U.S. side of the Joint U.S.-Japan Working Group on Reassessment of A-bomb Dosimetry, which oversees the study. The letter "robs our work of its significance," complains Masaharu Hoshi, a radiation biophysicist at Hiroshima University and a member of the working group, which includes 30 to 40 scientists from the U.S., Japan, and Europe.

Straume says he was abiding by a decision made at a January 2003 meeting that allowed his group to publish "as long as we did not compare our measurements to the DS02 calculations." And although the paper thanks two Japanese researchers for providing samples, Straume says his team decided that their contribution fell short of the "significant intellectual contributions" needed to become an author. Young disagrees, noting that the scientists went far beyond providing samples. Hoshi says that the Nature paper has poisoned the well against future collaborations.