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A technique for neutron dosimetry and spectrometry based on neutron activation of different metal discs has been studied. After exposure to a neutron field, the radionuclides produced in the discs are detected using low-level gamma-ray spectrometry and the neutron spectrum is obtained using a spectrum unfolding technique. In order to validate the method, irradiation was performed in a well-characterised (252)Cf neutron reference field. Furthermore, the detector was used to determine the neutron fluence rate and spectrum at a storage place for MOX nuclear fuel. The results of the two measurements are reported and discussed.

As a result of the introduction of the ICRP 60 recommendations and the increasing contribution of the neutron dose to the total dose of the personnel at the Belgonucleaire Mox fuel fabrication plant, the BD-PND bubble detector manufactured by Bubble Technology industries was introduced as a new, reliable personal neutron dosimeter. In the framework of the evaluation program of the bubble detector, measurements and calculations of the neutron spectra in the installations of the fuel fabrication plant were performed. The measurements were carried out with a ROSPEC neutron spectrometer, and the calculations were performed by means of the Monte Carlo code MCNP 4A. Comparison between measurements and calculations revealed good agreement. On the basis of the obtained neutron spectra, a correction factor was determined to take into account the new ICRP 60 recommendations and the difference between the calibration spectrum of the bubble detectors and the observed neutron spectra at the plant. This correction factor was applied to the calibration factor provided by Bubble Technology Industries.

The Institute for Reference Materials and Measurements operates a 7.0 MV Van de Graaff accelerator to generate monoenergetic neutron radiation for experimental applications. Owing to increased intensities of generated neutron fields and the more stringent regulation related to the maximum dose for the public, a concrete shielding wall surrounding the experimental building was constructed. This paper presents a study aiming at evaluating the effect of the shielding on the neutron field outside the wall. For this purpose, the following measurements were carried out around the building: (1) cartography of the neutron field for different experimental conditions; (2) measurement of neutron spectra using multiple Bonner spheres; (3) activation measurements using gold discs followed by low-level gamma spectrometry. From the measurements, it can be concluded that the wall fulfils its purpose to reduce the neutron dose rate to the surrounding area to an acceptable level.

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