Speaker
Description
Distributed networks of hybrid semiconductor pixelated detectors have proven their usefulness in characterization of mixed radiation fields, e.g. the ATLAS TPX network, which has provided data on particle flux within the ATLAS cavity at LHC over a span of several years by now; or the similar case at the MoEDAL experiment in the LHCb facility. In the framework of the Horizon 2020 funded MICADO project (Measurement and Instrumentation for Cleaning and Decommissioning Operations), we propose a long-term nuclear waste monitoring system based on Timepix3 technology as an alternative/complementary solution to the conventionally used detectors. Particle detectors based on Timepix3 are capable of particle discrimination and provide spectrometric information in common with precise timing information. The particle flux encountered by these detectors, depending on nuclear waste composition, volume, geometry and the distance between the waste packages and detectors, is expected to cover a challenging range and to be composed of mixed radiation field of ionizing and non-ionizing radiation. Moreover, in some cases, part of the detectors will be attached directly to the waste drums, while others are fixed to the storage walls. To maximize the versatility of the setup, the Timepix3 detectors employed are equipped with a range of different sensors, namely Si sensors with thicknesses of 100, 300, and 500 µm, as well as CdTe sensors with a thickness of 1 mm. To enable measurement of neutrons, two quadrants of the detectors are covered by neutron converters. Thermal and epithermal neutrons are detected below a $^6$LiF foil through products of a $^6$Li(n,α)$^3$H reaction and fast neutrons are visible through recoil protons under a polyethylene layer.
Energy calibration of all detectors was performed in the Institute of Experimental and Applied Physics of Czech Technical University in Prague, using an X-ray tube with several fluorescence foils and gamma rays from an $^{241}$Am source. The neutron detection efficiency calibration was performed at the Czech Metrology Institute by thermal neutrons from $^{238}$PuBe source moderated in a graphite prism and by neutrons from $^{252}$Cf and $^{241}$AmBe sources. A specific software for the Timepix3 network control and data acquisition was developed in-house. This software allows to reproduce and visualize particle fluxes and dose on-line in all detectors separately, as well as to combine quantities from some of them on demand. An early warning system in case of a specified increase of radiation is incorporated as well. First results of long-term laboratory test where various radiation sources were used to simulate radwaste will be presented. However, comprehensive measurements on radwaste sites are currently being prepared.
