Reactor dosimetry makes possible to characterize the neutron spectrum (neutron energy distribution) and to determine the neutron fluence received during irradiation for monitoring the embrittlement of materials. This technique relies on analyzing the radioactivity of irradiated dosimeters, made of pure metals or alloys of known compositions, some isotopes of which undergo activation or fission reactions.
There are numerous dosimeters sensitive to < 1 keV or > 2 MeV, a few between 1 MeV and 2 MeV, but Zr is the only one suitable for the energy range between 1 keV and 1 MeV. Moreover, few dosimeters respond with a threshold close to 1 MeV in moderate-flux R&D reactors. The only one practically usable, Rh, has a half-life < 1 h, and its measurement relies solely on highly self-absorbed X-rays, requiring very thin dosimeters and complicating measurements. There is therefore a real need to develop a dosimeter capable of responding between 1 keV and 1 MeV.
In this context, Xe not only exhibits an interesting reaction already identified between 1 keV and 1 MeV, but also has two reactions close to 1 MeV producing two nuclides with half-lives of about ten days, well suited to the irradiation cycles of the upcoming high-flux experimental reactor at CEA: the Jules Horowitz Reactor (JHR).
The main idea of this thesis topic would be to use adsorbent materials to trap a sufficient mass of Xe in a reduced volume. Some commercial zeolites can now trap up to 30% by weight of Xe when exposed to only 1 bar of Xe at room temperature.
The thesis will consist of producing a Xe dosimeter trapped on a zeolite at CNRS MADIREL (frequent trips to the Saint Jérôme campus in Marseille in the first year) as well as a simplified Xe-filled chamber manufactured in in the workshops of our laboratory. The common irradiation of a dosimeter and a chamber in a reactor such as CABRI in Cadarache will allow the evaluation of the self-absorption factors by the zeolite of the gamma lines emitted by the isotopes of interest, verification of their measurability with the MADERE platform of our laboratory, as well as assessment of the ageing of zeolites under strong neutron irradiation. The dosimeter will then be tested at higher neutron flux, for example in the TRIGA reactor at JSI (one-week trip to Slovenia to be expected), through the uninterrupted CEA-JSI collaboration since 2008, in order to qualify this dosimeter for JHR.
By acquiring expertise in the field of nuclear measurement, the future PhD graduate will be well prepared for professional integration into major French and international research organizations, or in nuclear companies.