(For previous posts on the accident, go here and here.)
Particle physics scientists at J-PARC are trying to show they are not like nuclear scientists (or nuclear plant operators) and released the result of analysis for gamma nuclides using the germanium semiconductor detector on the night of May 23, 2013, the day of the accident.
No mention of tritium, which is beta nuclide.
From the scanned images of the report on paper, published on May 25, 2013:
Hg (mercury) 197: half life 2.706 days
K (potassium) 43: half life 0.9294 day
Au (gold) 198: half life 2.695174 days
Hg (mercury) 195: half life 10.5306 hours
Na (sodium) 24: half life 14.9589 hours
There are numerous spikes indicating other radionuclides. But since it is a scanned image, I can't read the tiny print clearly.
The report also says the external radiation exposure was 0.1 millisievert (max). Almost all radiation exposure for the researchers, therefore, was from internal exposure as they inhaled the air inside the facility without realizing the gold used as target had been partially vaporized and radioactive materials, instead of staying inside the metal, were released in the air.
(English labels are by me)
The accident timeline in the report shows they continued the experiment after the equipment malfunction at 11:55AM, until 4:15PM when they used the survey meter to measure the radiation levels inside the hall. It was between 4 and 6 microsievert/hour, 10 times the normal level.
The ostensible reason for the delay in reporting the accident to authorities was that on May 23 they thought the contamination was only inside the radiation control area. That doesn't quite fly, as they say (in the accident timeline) that the radiation level (gamma) inside the hall dropped when the ventilation fan was used, and rose when they stopped using the fan.
So these particle physics scientists claim they didn't connect the dots at that time, and that they finally decided there had been radioactive materials leak outside the facility when they checked the monitoring post placed outside the facility in the evening of May 24. Another facility inside the J-PARC compound notified the Hadron Facility that their monitoring post showed elevated radiation level on May 23, precisely when the ventilation fan was being used, according to the report.
It looks like a much larger leak than first reported.
J-PARC's Hadron Experimental Facility, from their homepage: