May 25, 2013
 (Corrected June 3, 2013) 

Accident of J-PARC Hadron Experimental Facility

1. Date & time: 11:55 May 23, 2013
   
   
2. Place: Hadron Experimental Facility
   
   
3. Accident:
   
   In the Hadron Experimental Facility experiments were conducted with the elementary particles that had been generated by irradiating gold target with proton beams. The proton beam were extracted from the main ring (MR) within much shorter time than the normal operation due to the malfunction of the beam extraction system and the gold target was bombarded with very short pulsed beam. As a result, it was suspected that the beam spot of the gold target had been heated up spontaneously and the part of the gold target had sublimed. Radioactive materials that had been generated with proton beam irradiation leaked from proton beam equipment to the experimental hall and the experimenters in the hall were exposed to the radiation. The number of personnel who entered radiation controlled area and got close to the equipment was 55.
   

   The Hadron Experimental Facility is now shut down.
   The contamination in the Hadron Hall is roughly 30 Bq/cm2.
   The Hadron Hall has been shut out and the entry to the hall has been prohibited.
   The measurements of radiation exposure are being carried out for the experimenters and the maximal exposure was 1.7 mSv so far.
   
   
4. Effects:
   
   The radiation monitors around the Hadron Hall showed slight increase, but the monitoring posts at the site boundary did not show any meaningful increase. Two monitoring posts and a monitoring station in the neighboring laboratory observed the temporary increase of 6 nGy/h, where normal indication is 70 to 130 nGy/h. The amount of emission of the radioactive materials to the environment is being surveyed.