A Personal Neutron Dosimetry System Based on Etched Track and Automatic Readout by Autoscan 60

Abstract

An instrument for reading chemically etched CR-39 elements, the Autoscan 60, has become commercially available. Based on this readout system a new personal neutron dosemeter badge has been developed. PN3 detectors (NE Technology) are used with a two step etching process. The radiators are polyethylene (PE), polyethylene with 6 Li and aluminium. In a nuclear reaction of 6 Li with thermal neutrons alpha particles and tritons ( 3 H) are produced. While the range of alpha particles (9 μm) is too short to be detected with a two step etching procedure, tritons (range = 52 μm in CR-39) easily reach the sensitive layer of the detector and increase the response for thermal neutrons to a value determined by the 6 Li concentration in the PE radiator. Aluminium inhibits the production of recoil protons and hence, causes a lower response to fast neutrons as compared to PE. From the ratio of the readings behind PE and Al, spectral information can be derived, especially in accident situations when the track density is high and a radiation field analysis is required. For extremely high track densities a microscope is used for evaluation, since automatic counting by Autoscan 60 saturates at doses above 50 mSv. The system has been tested for reproducibility, linearity, energy dependence up to 66 MeV neutron energy, angular dependence, radon background response and multiple use of CR-39 detectors.