Toshiyuki Kumatori, a prominent figure in radiological sciences who treated radiation victims of the 1954 U.S. hydrogen-bomb test at Bikini Atoll in the Central Pacific, died Saturday from pneumonia at a hospital in Saitama Prefecture. He was 83.

Kumatori served as chief doctor for 16 of 23 crew members of the fishing boat Fukuryu Maru No. 5.

The Fukuryu Maru, known in English as the Lucky Dragon, was exposed to radiation during the hydrogen-bomb test in the Marshall Islands in March 1954. Kumatori concluded that the cause of death of crewman Aikichi Kuboyama was radiation exposure.

Kumatori was working at National Tokyo No. 1 Hospital, now the International Medical Center of Japan, at the time.

Kuboyama, the ship’s chief radio operator, died about six months after the incident, becoming in the process the first documented person to die from radiation exposure from a hydrogen bomb.

The crew of the boat from Yaizu, Shizuoka Prefecture, were fishing for tuna about 160 km east of the test site at the time of the explosion. The bomb was 1,000 times more powerful than the atomic bomb dropped on Hiroshima.