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Photon radiation induced decolourisation of radiochromic film changes its optical density. The photon dose is thereby evaluated as a function of optical density. The detection limit of common radiochromic films lies between 1 cGy and 20 Gy. This paper describes a novel evaluation method of radiochromic films using cosine-distance analysis of the RGB-colour vectors instead of conventional optical density measurements using a scanner in transmission mode. This allows extending the detection limit to excess of 40 Gy. • Gaf-EBT3 radiochromic films exposed to photons from 6 MV linac. • RGB colour histogram constructed using ImageJ program. • Cosine-distance (CD) calculated using RGB colour vectors. • Photon doses presented as a function of CD. [ABSTRACT FROM AUTHOR]

Abstract: On 27 April 2006 a vacuum ultra violet free electron laser (FEL) named free electron laser in Hamburg (FLASH) producing intense beams of 13.1nm laser light became operational. A 260m long, 1GeV superconducting electron linear accelerator (linac) drives the FLASH. The electron linac is made of an array of superconducting niobium cavities developed at DESY on TESLA technology. During the FEL operation a parasitic radiation field of photoneutrons and bremsstrahlung gamma rays persists in the linac containment tunnel. Sophisticated measurement and control devices, based on radiation-sensitive commercial off the shelf (COTS) microelectronic components, have been installed near the FLASH linac. Therefore, it becomes necessary to characterise these stray radiations, in order to predict the radiation effects on electronics. This paper summarises the features of novel radiation dosimeters and accelerator dosimetry techniques developed by our group. The utilisation of valuable radiation dosimetry data gathered from the experiments at FLASH to predict the radiation field characteristics of the future European X-ray free electron laser (XFEL) driven by a 20GeV superconducting electron linac is highlighted. [Copyright &y& Elsevier]

Bremsstrahlung gamma radiation and photoneutrons are predominantly produced during the operation of high-energy electron linear accelerators. Therefore, generated radiation could cause radiation damage of electronic devices installed in the accelerator tunnel. A real-time radiation monitoring system RadMon has been designed to monitor both types of radiation at crucial spots inside a free electron laser FLASH. Several different versions of readout systems were designed and tested to choose the most suitable architecture for the cost-effective readout of the radiation monitoring system RadMon. [ABSTRACT FROM AUTHOR]

This paper discusses a system for an on-line neutron fluence monitoring at linear accelerators. The system consists of a SRAM-based detector and a radiation-tolerant read-out system. The neutron fluence was measured in several locations of the accelerator. Monitoring of the radiation environment in an accelerator tunnel is necessary to assure reliable long-term operation of electronic systems placed in the tunnel. Monitoring of the chamber is especially important during the design stage of a linear accelerator. The new design of 20 GeV linear accelerator X-ray Free Electron Laser (X-FEL) 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 Vacuum UltraViolet Free Electron Laser (VUV-FEL). The application of a pair of TLD-700 and TLD-500 or superheated emulsion (bubble) dosimeters enables the supervision of neutron fluence in accelerators [3]. This process requires continuous and arduous calibration of TLDs, therefore this method is not convenient. Moreover, it is impossible to monitor the radiation environment in real-time. The presented system fills the market niche 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 the diagnosis and reduction of 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, α) source 241AmBe. The systems were installed in two accelerators: Linac II and VUV-FEL. [ABSTRACT FROM AUTHOR]