A distributed System for Radiation Monitoring at Linear Accelerators

The paper presents a system for an on-line neutron fluence monitoring at a linear accelerator. The system consists of a SRAM-based detector and a radiation-tolerant read-out system. The neutron fluence is measured in several locations of the accelerator. Monitoring of the radiation environment in an accelerator tunnel is necessary to assure a reliable long-term operation of electronic systems placed in the tunnel. The monitoring of the chamber is especially important during the design stage of a linear accelerator. The new design of 20 GeV linear accelerator X-FEL (X-ray Free Electron Laser) is currently approved for construction at DESY Research Centre in Hamburg [1], [2]. The presented paper is based on our research and experimental measurement carried out at 1.2 GeV superconducting electron linac driving the VUV-FEL. The application of a pair of TLD-700 and TLD-500 or superheated emulsion (bubble) dosimeters enables the supervision of neutrons fluence in accelerators [3]. This process requires continuous and arduous calibration of TLD, therefore this method is not convenient. Moreover, it is impossible to monitor the radiation environment in real time. The presented system fill the market nitche of real-time neutron monitoring for high-energy accelerators. Neutron fluence and gamma dose measured in this way can be used for the detailed analysis of the VUV-FEL or X-FEL environments. Monitoring of the radioactive area in a linear accelerator tunnel could be helpful to diagnose and reduce beam losses [4], [5]. We have conducted experiments with the distributed system dedicated to neutron flux measurement at the DESY Research Centre in Hamburg. The devices were exposed to a neutron field from an Americium-Beryllium (n, alpha) source 241 AmBe. The systems were installed in two accelerators: Linac II and VUV-FEL.