LIP - Detalhes

The need of thermal neutron detectors for use at nuclear reactors and spallation sources as well as for applications related to homeland security and radiological protection continues to grow. The detector is a key component in instruments dedicated to materials research (e.g. neutron scattering instruments) and in neutron radiography and tomography. Neutrons as a non-ionizing radiation cannot be detected directly; they can only be detected through the reaction products in converter materials. Only a few isotopes can be used for this purpose, e. g.: He-3, Li-6, B-10, Gd-157. Until recently, the isotope most commonly used in position sensitive thermal neutron detectors was He-3. Unique properties of this isotope allowed to design detectors with excellent performance (detection efficiency ~100%, position resolution ~ 0.5 mm FWHM, low sensitivity to gamma radiation). Given the world shortage in H-3, his price is presently attaining a forbidding level, moreover at the current rate of usage the stock of He-3 in the USA will be exhausted by 2024. Despite the efforts in the search for He-3 alternatives, adequate high spatial resolution, high count rate detectors do not exist today for a significant number of instruments, particularly at the highest flux sources, and the necessary technological developments are urgently needed. Boron-10 with a thermal neutron capture cross section of ~3840 barn (~72% of the cross section for He-3) is one of the most promising alternatives to He-3 isotope. Boron-10 has an occurrence in natural boron of ~20%, which has an average abundance on earth. This project aims to develop a new position-sensitive neutron detector concept, based on the well established RPCs (Resistive Plate Chambers) technology as a potential future alternative to He-3 detectors. Our idea is to use resistive electrodes coated with a thin film (1-2 micron) of a B4C solid neutron converter in a multi-gap RPC configuration. This approach takes advantage of the naturally layered configuration of RPCs which is needed to ensure high neutron detection efficiency. We intend to demonstrate that this type of detector can be successfully applied for 2D positioning of thermal neutron events with high spatial resolution (sub-mm regime). For higher resolution detectors, in the range 1-3mm, estimates of detector requirements for ESS (European Spallation Source) instruments show that there is a clear requirement gap between desired detector performance and the best that is currently available. Preliminary studies have been conducted and priority was given to the realization of the basic ingredient for the implementation of the concept, i.e., the B4C coatings. Recently, we received the first samples coated with B4C, enriched in B-10, provided by Dr. Carina Höglund (Linkoping University, Sweden), responsible for the large area B4C coatings production for our partners (e.g. ILL: “Multi-Grid Project”; TUM: “Boron-10 based detector with stacked macro-structured cathodes”). In a next phase, it follows up the study of a B4C coated RPC prototype (cathode coated with B4C, enriched in B-10) with thermal neutrons, in order to complete the concept's feasibility tests. The development of the idea herein described is being held in the framework of an exploratory project funded by FCT (EXPL/FIS-NUC/2522/2013) and which will end in August 31, 2015. This project is being developed in close collaboration with international partners (e.g. ILL, TUM-FRM II, ESS). Furthermore LIP integrated an international consortium of 18 beneficiaries led by the European (ESFRI) facilities, ILL and ESS, which submitted in September 2014 a Horizon2020 proposal “World class Science and Innovation with Neutrons in Europe 2020 – SINE2020” (Call: H2020-INFRADEV-1-2014-1, Proposal No.: 654000). LIP has under his responsibility the task “Resistive plate chambers (RPCs)” part of the research activity “Emergent Detector Technologies for Neutron Scattering and Muon Spectroscopy”, coordinated by ESS (resources committed to LIP: ¤ 116,250). The continuity of the research work of this project is also foreseen in the framework of a National project submitted to the FCT on 29/01/2015: PTDC / FIS-NUC / 6742/2014, Resistive Plate Chambers for next-generation of cosmic-ray and neutron detectors, wherein Prof. Paulo Fonte is the Principal Investigator.