At the Paul Scherrer Institute, the new SwissFEL Free Electron Laser facility is currently in the design phase. It is foreseen to accelerate electrons up to a maximum energy of 7 GeV with a pulsed time structure. An injector test facility is operated at a maximum energy of 300 MeV and serves as the principal test and demonstration plant for the SwissFEL project. Secondary radiation is created in unavoidable interactions of the primary beam with beamline components. The resulting ambient dose-equivalent rate due to neutrons was measured along the beamline with different commercially available survey instruments. The present study compares the readings of these neutron detectors (one of them is specifically designed for measurements in pulsed fields). The experiments were carried out in both, a normal and a diagnostic mode of operation of the injector.

Proton therapy is a widely used method of cancer treatment. Undesired secondary particles such as neutrons accompany the irradiation. Depending on the measurement position, the expected main dose contribution due to undesired secondary particles arises from neutrons with energies >20 MeV. Conventionally used Andersson and Braun-type survey instruments may underestimate the ambient dose equivalent up to a factor of 2 due to their limited response for high-energy neutrons. Therefore, it is desirable to investigate the neutron stray field in conditions comparable to therapy treatment, in particular the resulting dose to equipment placed in the treatment vault to estimate possible consequences to its operation. The irradiation of a water phantom with 200-Me V protons adequately reproduces these conditions.