The Lives of Two A-bomb Scientists, Part 3

by Hiromi Morita, Staff Writer

Conducting research in the United States

Hiromi Hasai, who took a two-year leave of absence from the Faculty of Engineering at Hiroshima University to battle tuberculosis, recovered from the disease and returned to school. He then attended a non-degree course for graduates. In 1958, he was invited to work as a research assistant at the Nuclear Physics Laboratory, which marked the beginning of his career as a physicist. He was 27 years old at the time.

More than 20 years would pass, though, before he could squarely face his experience of the atomic bombing. The fact that he had survived, when so many died, left him laden with guilt.

In 1981, he went to the United States to conduct research and visited the Los Alamos National Laboratory in New Mexico, the site where the atomic bombs dropped on Hiroshima and Nagasaki were developed. The American scientists at the laboratory, who handled massive experimental equipment, took reflexive pride in their nuclear weapons.

Dr. Hasai felt that something was wrong. As he began to believe that he needed to learn more about Hiroshima, he met Masaharu Hoshi in the United States, who had been sent by the Research Institute for Nuclear Medicine and Biology at Hiroshima University. (Now known as the Research Institute for Radiation Biology and Medicine.)

Measurement of residual radiation

In those days, the radiation doses suffered by atomic bomb survivors (hibakusha) was estimated based on the data gleaned from nuclear tests in the U.S. state of Nevada. Dr. Hoshi, who was engaged in a reassessment of those estimated doses in light of the actual doses measured in Hiroshima, asked Dr. Hasai to work with him on this project.

Returning to Hiroshima, Dr. Hasai and his colleagues collected more than 2,000 samples from a range of objects, including buildings, bridges, shrine gates, and gravestones, and then measured the residual radiation doses of these samples. In 1986, as these measurements continued, Japan and the United States jointly developed the Dosimetry System 1986 (DS86), a new method for estimating radiation doses suffered by hibakusha.

But there were discrepancies between the U.S.-led theoretical calculation and the actual doses of radiation measured by Dr. Hasai and others. The suspicion that neutron doses were underestimated as the locations of hibakusha extended farther from the hypocenter lingered.

Dr. Hasai, with others, continued to verify the accuracy of radiation measurements. They also initiated workshops with experts in Japan.

The estimates of radiation doses suffered by hibakusha serve as the foundation of the international standard for radiation protection. Before long, the U.S. could not disregard the research by Dr. Hasai and Dr. Hoshi. In 2001, the U.S.-Japan Joint Workshop for Reassessment of Atomic Bomb Radiation Dosimetry in Hiroshima and Nagasaki was established to review DS86 and develop a new method called the Dosimetry System 2002 (DS02). Dr. Hasai became the chairperson of the Japanese side of the workshop and a member of its Joint Senior Review Group.

Though Dr. Hasai was able to improve upon DS86, he still felt a gulf between the Japanese side and their U.S. counterparts. “The U.S. was out to produce nuclear weapons and sought the data for this purpose,” he explained. “The Japanese, though, wanted to know the real horror of the damage caused by the radiation. So, right from the start, we stood on different footing. We sometimes talked at cross purposes.”

For instance, the U.S. side tried to dismiss the effect of radiation exposure at locations more distant from the hypocenter as “a minor problem.”

But Dr. Hasai persisted: “I’m a hibakusha, too. I can’t ignore the possible effects of radiation exposure at the more distant locations.”

Participation in workshops

Shoji Sawada was, at the time, involved in the “Matsuya lawsuit over A-bomb disease certification in Nagasaki.” Ms. Matsuya, the plaintiff, was exposed to the atomic bombing of Nagasaki and had sought the A-bomb disease certification. However, she became embroiled in a legal battle from 1988 to 2000, when the Supreme Court finally ruled in her favor. Citing DS86, the Japanese government would not recognize that the plaintiff’s disease, since she experienced the atomic bombing at some distance from the hypocenter, was induced by the atomic bombing. But the Supreme Court ruling said that DS86 had unresolved problems and criticized its application.

Dr. Sawada, who submitted a written opinion to the court, realized anew the limitations of DS86. He then offered to take part in the workshops initiated by Dr. Hasai and others. The atomic bombs brought the two scientists together again.

The Dosimetry System 1986, or DS86, is a method jointly developed by the U.S. and Japan in 1986 in order to estimate radiation doses from the atomic bombings. This system enables the radiation doses of individual hibakusha to be estimated based on the total amount of initial radiation released within roughly one minute of the explosion of the bombs, the locations of the hibakusha, and the conditions that may have provided some shielding to them. The Dosimetry System 2002, or DS02, which can produce more accurate estimates, was adopted in 2003.