Ultra High Sensitive Neutron Dosimetry by detection of trace elements produced through nuclear reactions in Reactor Structural Materials with Resonance lonization Spectroscopy

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The present study is aiming at the development of ultra high sensitive neutron dosimetry technique with Resonance lonization Spectroscopy (RIS) as an alternative for conventional methods based on radioactivity measurement. The RIS system combined with an ion mass spectrometer is applied to the measurement of concentration and/or isotopic distribution of trace elements produced by nuclear reactions with neutrons, in particular for the detection of stable and/or long-lived radioactive isotopes on reactor structural materials at ppb level concentration with little or no background from isobaric interferences. The basic experiments and theoretical consideration have been made to establish this new methodology including the data analysis for neutron dose estimation.The main research results are summarized as follows;1. A prototype RIS system was fabricated for detection of trace elements in gaseous and solid samples, and the basic system performance such as a detection limit was made clear through Xe gas analysis.2. Efficient RIS schemes for SUS elements after neutron irradiation were theoretically investigated and verified through experiments. In particular, a theoretical model was developed on resonant laser ablation, which can well explain the experimental results on the dependence of ion yields on incident laser power and wavelength. In addition, by improving the ion extraction to a mass spectrometer, it was shown that the detection sensitivity could be much higher than that of the conventional radioactivity measurement.3. A new method for neutron dose estimation was developed on the basis of neural network, which would be suitable for RIS data pattern analysis. Through examples of neutron spectrum adjustment from activation foil data, it was found that the present method has potential advantages over the conventional ones in computational simplicity and solution validty.