In the frame of its activity related to the development of standard neutron fields, aimed at calibrating radiation protection devices, the Laboratory for micro-irradiation, neutron metrology and neutron dosimetry (LMDN) of the Institute of Radiation Protection and Nuclear Safety (IRSN), has to develop new neutron fields to meet emerging needs and also meet the recommendations of international standards (ISO 12789). In particular, the LMDN would like to propose in middle-term: -new realistic fields, whose energy distribution is more representative of that encountered at nuclear industry workplaces -meet at best the new needs for calibration in the epithermal field and for which there is no reference field to date. The thesis proposal concerns the development of realistic and epithermal neutron fields as well as the study of a neutron spectrometry method dedicated to their characterization, in an energy range from 0.5 eV up to 10 keV. The work will be organized around three main components: -the design, by means of Monte Carlo simulations, of several realistic fields whose energy distributions have been defined by the laboratory during a preliminary study. The candidate will then actively participate in the realization phase and experimental characterization. -the second and third components will concern the design of an epithermal neutron field and the development of a spectrometer or a measurement method for the characterization of the energy distribution of the new epithermal field. The design of an epithermal field will be studied by Monte Carlo simulation by exploiting the diversity and the characteristics of all the LMDN neutron facilities, the “T400” or AMANDE accelerators or even the Van Gogh irradiator (radionuclides sources). The implementation of the device will be entrusted to an external company but the doctoral student will participate highly in the development phase of the specifications. A second phase of this work will concern the characterization of the neutron field produced with the existing reference spectrometry instruments used by the laboratory and the comparison with the values predicted by simulation. In parallel, new methods of spectrometry and determination of dose equivalents in the epithermal domain will be developed. Several reference neutron spectrometry systems are used in the laboratory, but none specifically covers the epithermal domain. Some detectors respond favorably in the epithermal domain, they consist of a proportional gas counter filled with 3He which is placed in turn in the center of polyethylene spheres of a few centimeters in diameter. A combination of different spheres of material and size suitable for epithermal neutrons could be investigated. Other detection methods considering, for example, fission chambers, activation or innovative systems will be studied. In the framework of this thesis, several papers will have to be published in peer-reviewed journals, in English.