Residual Radiation Monitoring by Beam Loss Monitors at the J-PARC Main Ring

At J-PARC (the Japan Proton Accelerator Research Complex), high intensity proton accelerator, controlling and localizing beam losses and residual radiations are key issue, because the residual radiation limits maintenance work in efficiency and working hours, and then limits machine availability. We are accumulating continuous measurement data of residual radiation after beam stop using beam loss monitors in the Main Ring (MR). The wire cylinder gaseous radiation detectors are used in a proportional counting region. The heads are DC-connected and have a gain as large as 30000 with a bias of -2 kV. We switch the DAQ trigger from "Beam Trigger" to "No Beam Trigger", change the ADC sampling rate to 16 ms, and raise the gain by changing the bias voltage from -1.6 kV to -2.0 kV with a few exceptions when the accelerator operation ends. The offsets are measured with zero bias voltage. Identification of radionuclides has been performed with time decay analysis, with assistance of energy spectrum measurements with the Gamma Ray Spectrometer, Kromek GR1-Spectro.