Neutron spectrometry in mixed fields: proportional counter spectrometers.

Proton recoil proportional counters have been successfully used in many laboratories worldwide for more than 30 years in order to measure high-resolution neutron energy spectra. The method is well elaborated and understood, nevertheless high expertise is required for its proper application. Table 4.1 summarises typical basic data for proton recoil proportional counters and the requirements for their application. It is noteworthy that any limiting parameter can vary to a certain degree depending on the quality of the detectors used (design, gas purity, response functions, etc) and their response matrices, the data analysis and the unfolding procedures applied with a correct evaluation of the uncertainties involved. It is also important to lend a critical eye to details during measurements (e.g. environmental and electronics problems) as well as in subsequent analysis and unfolding (e.g. oscillations due to unfolding artefacts or inadequacies in detector response matrices). It is recommended that any spectrometry system (procedures for measurement and data evaluation) should be tested and validated in well-known neutron fields e.g. 252Cf standard fission or 241Am-Be. One should, however, expect that, due to different room scatter conditions, deviations from the ISO spectra may occur, especially for low neutron energies. In order to demonstrate the capability of the recoil proton counter technique, two examples of typical neutron spectra are shown in Figures 4.20 and 4.21, both measured in mixed neutron-gamma fields at nuclear research reactors.