| We would like to express all our deepest apologies for any disruptions and concerns that may have been caused by the leakage accident of radioactive material at the Hadron Experimental Facility of Japan Proton Accelerator Research Complex (J-PARC) in Japan.
On 23 May, due to a malfunction of the beam extraction system of the 50 GeV synchrotron, a proton beam was delivered to the gold target of the Hadron facility within a very short time. As a result, the gold target is considered to have momentarily reached an extremely high temperature and part of the target was damaged. Radioactive material then leaked into the hadron experimental hall and some workers externally and/or internally exposed to radiation.
Operation of ventilation fans of the hall resulted in the leak of radioactive material out of the radiation controlled area of the Hadron Experimental Facility. The data logs of radiation dose rates at monitoring posts in the Nuclear Science Research Institute showed no signatures. However, at the three monitoring posts and stations of the neighboring JAEA facility, momentary increases of the radiation dose rate were observed. It is assessed that the released radioactive material was diluted and attenuated as it dispersed in a narrow strip towards the west. The maximum integrated radiation dose has been estimated even at the site boundary closest to the Hadron Experimental Facility was 0.29 µSv (preliminary) .
All the J-PARC facilities have been shutdown since the accident. A full investigation of the cause of the accident is now underway along with the complete review of safety practices and emergency procedures at all J-PARC facilities. Our first priority is to restore public trust in the facility by developing and implementing measures to prevent the reoccurrence of an accident and to provide a safe experimental environment for users and workers.
We would deeply appreciate your understanding and continuous support. Yujiro IKEDA Director J-PARC center|