An empirical formula for the residual dose rate of the collimator section of the J-PARC MR

Taking into account a hands-on maintenance scenario, a residual dose rate at a working area should be controlled to be lower than 1 mSv/h. At present, beam power loss at the collimator section due to strong activations is restricted to 300 W, rendering it impossible to reach the 750 kW beam power the J-PARC MR was designed to achieve. Severe activation control is essential for future beam intensity improvement. To obtain reasonable predictions of future activation level, an empirical formula was obtained by fitting measured data with a modified Sullivan-Overton formula. Using the formula, the activation level after 30 years of beam operations was derived. We present in this article the details of the data analysis. (author)