Health Physics Aspects of 20- to 40-MeV Linac Operations

The AFRRI electron linear accelerator is a two-mode, high-current (1-3 A) LINAC used for research in radiobiology, biological inactivation, and radiation effects on electronic devices. Operations are predominantly in the ranges of 13-20 MeV and 35-40 MeV, which results in contrasting health physics problems. Low-energy operations are dominated by the production of toxic gas (ozone) and by some localized activation for bremsstrahlung operations. Ozone concentration is constantly monitored for electron-in-air operations. Problems with high-energy operations are related to target configuration and experimental design. This includes activation of various machine and experimental components and activation of room air. For some operations, ozone can also be a serious problem. A monitoring system was devised to distinguish between the 15O and 13N air-activation components. Cooling water activation, resin bed activity levels, klystron X ray leakage, removable surface contamination, and gamma and neutron streaming are seen, but have not been significant problems.