Scientists continued to conduct beam bombardment experiments in a nuclear physics laboratory last month for 37 hours after radioactive materials leaked in an adjacent lab, sources said.
Scientists continued to conduct beam bombardment experiments in a nuclear physics laboratory last month for 37 hours after radioactive materials leaked in an adjacent lab, sources said.
The leak occurred around 11:55 a.m. on May 23 at the Hadron Experimental Facility of the Japan Proton Accelerator Research Complex in Tokai, Ibaraki Prefecture.
J-PARC informed the Nuclear Regulation Authority, the Ibaraki prefectural government and others of the leak around 9:30 p.m. on May 24, but the Materials and Life Science Experimental Facility laboratory next door to the Hadron lab continued with its beam experiments until 12:46 a.m. on May 25.
Both laboratories share the same system of particle accelerators, or synchrotrons.
The NRA is investigating the case, which may constitute a violation of J-PARC's in-house operation manual, which says beams and equipment should be turned off in the event of a serious accident.
"Our senior officials, busy dealing with the aftermath of the accident, took time in instructing individuals in charge of the synchrotrons to stop the experiments," a J-PARC public relations official said.
The Materials and Life Science Experimental Facility is used in experiments for protein analysis, drug discovery and development of new materials.
At J-PARC, particle beams first travel around a rapid cycling synchrotron, which has a perimeter length of 350 meters, and are then guided into a 1,600-meter main ring synchrotron for further acceleration. The Hadron Experimental Facility was using beams from the main ring, whereas the Materials and Life Science Experimental Facility was using beams from the smaller ring.
J-PARC suspended experiments along the main ring about four hours after the leak started, but it did not halt the experiments using the smaller ring.
An NRA official said J-PARC was apparently late in stopping the experiments because it initially did not realize how serious the leakage was.
The High Energy Accelerator Research Organization and the Japan Atomic Energy Agency, which jointly operate the synchrotrons, were expected to convene a meeting of a third-party expert panel on June 21 to investigate and evaluate safety controls.