Individual neutron monitoring with CR-39 detectors at an accelerator centre

A new personal neutron dosimetry system at the Paul Scherrer Institute (PSI) is based on chemically etched CR-39 detectors (PN3) with different radiators, and an automatic readout system, the Autoscan 60. The most relevant neutron fields at the PSI accelerator have an energy range up to 600 MeV with peak energies around 1-5 and 50-100 MeV due to evaporation and cascade processes in the concrete shieldings, and partly thermalised spectra that occur at the entrance to the labyrinths. The main radiators used for PN3 are polyethylene (PE) for fast neutrons and PE with lithium for thermal and fast neutrons. For extremely high track densities (corresponding to a dose up to 5 Sv) a transmission spectrometer is used for evaluation, since automatic counting by Autoscan 60 saturates at doses above 100 mSv. The system has been tested for linearity, energy dependence up to 300 MeV neutron energy, angular dependence, and radon background response. It was then calibrated for realistic neutron fields at PSI. The detection Limit for these high energy fields is about 0.3 mSv. In addition, calculations have been performed to determine the response of the dosemeter to typical spectra in nuclear power plants.