Neutron field characterisation in a high-energy proton-synchrotron environment using bubble detectors

During the beam adjustment of high energy accelerator facilities, a significant number of energetic particles impinge on the internal wall of the vacuum chamber thereby causing the production of intense parasitic radiation field, resulting in a short-term radiation exposure to personnel as well as interference in the operation of accelerator instrumentation systems usually based on sophisticated microelectronics. High-energy particle accelerators operate in pulsed mode; therefore, commercially available, general purpose radiation detectors for health physics activities are unsuitable for the assessment of such radiation field due to “pulse pile-up” effects. Hence, we have used passive neutron dosimeters, i.e. temperature compensated superheated emulsion (bubble) detectors of types BDPND and BDT, to evaluate the neutron fluence at three selected locations of the 7.6 GeV proton synchrotron operated by DESY: (a) the 1.2-m thick concrete shielding roof of the experiment hall housing the proton synchrotron, (b) the 0.9-m thick shielding roof of the proton injector hut, and (c) at the lateral wall (2.5 m concrete and earth shielding) of the experiment hall, facing the proton injector delivering 7.6 GeV protons into the PETRA booster ring.