Main goal of the project CZELTA (CZEch Large-area Time coincidence Array) is to study global properties of high-energetic cosmic rays. To present date, project consists of 5 stations covering large area in the Czech republic capable of detection of extensive air showers with energy exceeding 10¹⁴ eV. Such a network of distant stations can be an ideal tool for probing global structure of cosmic rays. We present the design of the detection system and obtained results

A novel experimental approach to search for double electron capture (EC/EC) is discussed in this article. R&D for a new generation EC/EC spectrometer based on silicon pixel detectors (SPDs) has been conducted since 2009 for an upgrade of the TGV experiment. SPDs built on Timepix technology with a spectroscopic readout from each individual pixel are an effective tool to detect the 2νEC/EC signature of the two low energy X-rays hitting two separate pixels. The ability of SPDs to indentify α/β /γ particles and localize them precisely leads to effective background discrimination and thus considerable improvement of the signal-to-background ratio (S/B). A multi-SPD system, called a Silicon Pixel Telescope (SPT), is planned based on the experimental approach of the TGV calorimeter which measures thin foils of enriched EC/EC-isotope sandwiched between HPGe detectors working in coincidence mode. The sources of SPD internal background have been identified by measuring SPD radiopurity with a low-background HPGe detector as well as by long-term SPD background runs in the Modane underground laboratory (LSM, France), and results of these studies are presented.

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The double beta decay (β β ) is very challenging subject of today's physics. It can be used as a powerful tool to test neutrino properties (e.g. Dirac or Majorana type of neutrino) and lepton number conservation. However, these experiments demand very high sensitivity and very strong background reduction. We have been performing intensive R&D towards the use of pixel detector Timepix in the β β decay experiments. The Timepix device, operated in Time Over Threshold (TOT) mode, provides spectroscopic capabilities in each individual pixel. The main advantage of such detector is its ability to identify and reject background signals (e.g. tracks made by electrons, alpha particles, muons). It would efficiently recognize the signal of β β decay processes. Two pixel detectors, Si (pixel size 55×55 µm 2 ) and CdTe (pixel size 110×110 µm 2 ), were tested in the surface laboratory as well as in the underground laboratories, from the point of view of intrinsic background and the results are presented. Low background materials for construction of the setup were also identified. The first prototype of Silicon Pixel Telescope (SPT) has been tested and future improvements are also presented.

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