Abstract
As part of its activities, the Laboratory for Micro-Irradiation, Metrology, and Neutron Dosimetry (LMDN), located in Cadarache, France, has an experimental facility that allows the generation of reference neutron fields. This facility includes, among other things, a platform called CARAT, equipped with a SAME T400 accelerator. Coupled with various moderators, this accelerator can generate realistic neutron fields (representative of those encountered in nuclear industry workplaces) as well as predominantly thermal fields (En < 0.025 eV). To expand the range of reference neutron fields and meet the needs of the industrial sector, notably for detector calibration, or the medical industry, particularly with accelerator-based boron neutron capture therapy (AB-BNCT) on 10B, the LMDN aims to enhance its platform with an epithermal neutron field, with energies ranging between 0.5 eV and 10 keV, capable of delivering a dose of 1 mSv in less than eight hours of irradiation.The design of a first moderator was modeled for 3.3 MeV neutrons produced from the D(d,n)3He reaction available on the T400 accelerator. Simulations conducted using the Monte Carlo code MCNP led to a design that met all constraints imposed by the laboratory (dose, mass, dimensions, neuron energy). However, a feasibility study showed that manufacturing the moderator was industrially complex due to the layering of different materials and exceeded the allocated budget. As a result, the fabrication of a moderator for the T400 accelerator was postponed.In the absence of a moderator, it was not possible to proceed with the second part of this thesis, which focused on the characterization of an epithermal neutron field. Therefore, a second moderator, more compact, cost-effective, and feasible within the timeframe of the thesis, was studied on the AMANDE accelerator using the 7Li(p, n)7Be reaction. This reaction was chosen for its threshold at 1.880 MeV, which allows to produce neutrons with an average energy of 30 keV, close to the reaction threshold. Thus, a few centimeters of high-density polyethylene can slow down these neutrons and create a field where the epithermal neutron flux contribution is higher than that of thermal and fast neutron fluxes.A first measurement campaign was carried out by the LPSC using the MIMAC fast-N detector to measure the energy of neutrons produced near the threshold of the 7Li(p, n)7Be reaction on AMANDE. This campaign confirmed the energy distribution measured of the neutrons with the distribution generated by the TARGET software, which is used to generate source terms for the MCNP simulations in this thesis. A second campaign, involving AMANDE’s moderator, was conducted in January 2024 using two detection systems. On the one hand, the neutron activation method using 197Au foils, a well-established method in neutron measurements, and on the other hand, a new detector, the Neutron Flux Monitor (NFM), developed by LPSC Grenoble. The NFM is a gaseous detector based on neutron capture by 10B. This detector was used in one of its first experimental campaigns. As part of this research, a method to determine the thermal and epithermal fluxes of the neutron field using the NFM was developed. These two systems provided complementary measurements of the thermal and epithermal neutron fluxes in the field. Finally, the experimental results were compared with Monte Carlo simulations performed using MCNP.
Key words
Epithermal neutrons, Neutron detection, Neutron activation, Metrology
Full text
Full text: https://theses.fr/2025GRALY003