Radiation mapping inside the Bunkers of medium energy accelerators using a robotic carrier

•Measurement and estimation of neutron and gamma radiation field prevailing inside active bunkers of Cyclotron during operation.•We can evaluate accident or worst-scenario radiation exposure to a human operator, utilizing the radiation field mapping.•The work has reduced un-wanted beam loss at undesirable spots.•Use of robotic carrier helped radiation field mapping during machine operation and reduced human labor.

The knowledge of ambient and peak radiation levels prevailing inside the bunkers of the accelerator facilities is essential in assessing the accidental human exposure inside the bunkers and in protecting sensitive electronic equipments by minimizing the exposure to high intensity mixed radiation fields. Radiation field mapping dynamically, inside bunkers are rare, though generally dose-rate data are available in every particle accelerator facilities at specific locations. Taking into account of the fact that the existing neutron fields with a spread of energy from thermal up to the energy of the accelerated charged projectiles, prompt photons and other particles prevailing during cyclotron operation inside the bunkers, neutron and gamma survey meters with extended energy ranges attached to a robotic carrier have been used. The robotic carrier movement was controlled remotely from the control room with the help of multiple visible range optical cameras provided inside the bunkers and the wireless and wired protocols of communication helped its movement and data acquisition from the survey meters. Variable Energy Cyclotron Centre, Kolkata has positive ion accelerating facilities such as K-130 room Temperature Cyclotron, K-500 Super Conducting Cyclotron and a forthcoming 30 MeV Proton Medical Cyclotron with high beam current. The dose rates data for K-130 Room Temperature Cyclotron, VECC were collected for various energies of alpha and proton beams losing their total energy at different stages on different materials at various strategic locations of radiological importance inside the bunkers. The measurements established that radiation levels inside the machine bunker dynamically change depending upon the beam type, beam energy, machine operation parameters, deflector condition, slit placement and central region beam tuning. The obtained inference from the association of dose rates with the parameters like beam intensity, type and energy of projectiles, helped in improving the primary beam transmission and minimizing the ambient radiation fields inside the bunkers.