History of RIKEN
Back from Beyond - Japan’s cyclotron, Part I
05 July 2006 (Volume 1 Issue 7)
The 160 cm cyclotron, completed in 1966, was central to the reconstruction of postwar RIKEN and Japan’s nuclear physics research.
RIKEN’s early days in the 1920s and 1930s coincided with a period of rapid progression in nuclear physics. One of the greatest achievements of this era was the development of a cyclotron, a type of a particle accelerator that effectively generates high-energy beams of atomic particles, such as protons and ions. Pioneered by Ernest Lawrence, a physicist at the University of California, in 1931, the device is used to study nuclear physics and in the development of diagnostic and medical procedures.
In 1937, Yoshio Nishina, a physicist at RIKEN and pioneer of quantum physics in Japan, led the development of the world’s second cyclotron—albeit a small one with a magnet pole of 65 centimeters in diameter. Nishina’s team completed construction of a bigger cyclotron (150 cm diameter) in 1943, and, in the following year, successfully tested a powerful beam of deuterons, which produce more energy in fusion reactions than protons.
However, this achievement couldn’t have come at a worse time for Japan. Soon after the beam experiment was completed, Japan surrendered in World War II in 1945. Suspicious that Japan was producing nuclear weaponry, the General Headquarters of the Allied Forces dissembled and dumped these two cyclotrons into Tokyo Bay. Physicists from the US lobbied to stop the action, but their efforts were in vain.
Devastated, Nishina nevertheless continued on to become the fourth president of RIKEN after it was dissolved and reorganized in 1948. He worked hard to resurrect RIKEN to its previous standing, but he passed away in 1951. Four months after Nishina’s death, Lawrence visited Japan and urged the revival of cyclotron research. Thanks partly to his support, in 1952 RIKEN built its third cyclotron with similar specifications to the first one. In the same year, Japan regained its independence and resumed atomic energy research.
In 1958, when RIKEN was inaugurated as a public corporation, the new president Haruo Nagaoka, a son of Hantaro Nagaoka, campaigned strongly for RIKEN to have a large cyclotron. Researchers thus hammered out a plan to develop a cyclotron equipped with a magnet pole of 160 cm in diameter. Nagaoka wanted to promote the ‘160 cm cyclotron’ as a symbol of the new RIKEN, which moved its headquarters to Wako, near Tokyo, in 1966.
Development of the 160 cm cyclotron began from scratch due to a dearth of postwar expertise, but RIKEN’s researchers never compromised their quest to better its performance. In 1966, the new cyclotron was completed and heralded Japan’s first capability to accelerate heavy ions — a brave decision on reflection, because, at that time, few thought that heavy ions would be a mainstay of nuclear research in the future.
By early the 1970s, this large cyclotron commenced 24-hour operation with strengthened beam power that allowed international researchers, from different research fields, to jointly use the equipment.
Using the cyclotron, RIKEN researchers zealously studied nuclear reactions and the scattering of helium-3 and heavy ions, while examining in-beam spectroscopy using alpha particles. In 1970, RIKEN commenced joint research with other scientists to produce short-lived radioactive isotopes. This work laid the foundation for developing medical imaging techniques such as Single-Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET).
Diversifying heavy-ion nuclear research using the 160 cm cyclotron bloomed in the 1970s, and led RIKEN to become one of the world’s leading research institutes in the field. Its contribution to medicine and physics until the halt of operation in 1990 is immeasurable, as some of this research paved the way for developing the next-generation of cyclotrons down the road.