The goal of this project is to develop an innovative detector – called GEMTEQ – for microdosimetry. Microdosimetry is the study of the temporal and spatial distributions of absorbed energy in biological matter and is crucial for the understanding of the relative biological effectiveness (RBE) of radiation on human tissue, for example of a carbon ion beam used in cancer treatments. The standard detector, the Tissue Equivalent Proportional Counter (TEPC), is based on a proportional counter made of tissue equivalent walls and detection gas. Operation of the gas at low pressure provides a magnification to micrometres in tissue. However, no spatial information in the detection volume is obtained and the magnification is not large enough to study radiation effects in detail at the size of the human cell structure.

The GEMTEQ detector is based on the GEMPix detector recently developed at CERN, which has already found several applications. It was designed by coupling two CERN technologies, a small triple Gas Electron Multiplier (GEM) (3×3×0.3 cm³ active volume) to a quad Timepix ASIC with 262,144 pixels of 55×55 μm² area each for readout. The operation as a Time Projection Chamber (TPC) allows for 3D track reconstruction with an outstanding spatial resolution thanks to the pixelated readout. However, the development of the GEMTEQ detector will require a lot of R&D work: an upgrade to the next readout generation (Timepix3) that allows time and energy measurements simultaneously; a low-pressure operation mode that directly increases the magnification; a sealed detector version that simplifies operation. It will be necessary to characterise the new GEMTEQ detector in operation with tissue equivalent gas and to compare it to the TEPC, the gold standard in microdosimetry. ARTEL, a company that has already gained experience with the GEMPix, will produce two prototype detectors, including the latest developments in the technology for example for better homogeneity of the electric field, while developments, tests and characterisation will be performed by CERN.

The GEMTEQ detector will introduce a radically different technology in the field of microdosimetry and significantly improve the spatial resolution allowing to go down to the 100nm level. Therefore it will pave the way to new research fields, which will add to the knowledge of irradiation processes and may help to improve radiation therapy. All scientific results will be made public.