JRA8-ASTRA: Advanced ultra-fast solid STate detectors for high precision RAdiation spectroscopy

ASTRA’s main objective is to develop beyond state-of-art advanced radiation detector systems, able to perform highprecision measurements of photons in a (very) broad energy range, capable to operate in different environments/ conditions. The development of such new, advanced, high-performance detector systems in terms of efficiency, stability, linearity, energy resolution, compactness and acceptance is mandatory in hadron physics, and will allow to perform measurements never done before, due to a lack of suitable detectors, with a huge impact in our understanding of the fundamental laws of nature. Such systems will have a positive impact in nuclear and fundamental physics too, as well as in many other applications (medicine, biology, safety) or scientific studies (astronomy and synchrotron radiation). The recent developments by the participants, with world-wide recognized top-class performances, have already realised detectors/sensors with suitable electronics, mechanics support structures as well as part of them in cryogenics environment. The availability of facilities to characterize the whole detector system insures the perfect basis to fulfil the ASTRA strategy to develop advanced detector systems for extreme precision measurements of radiation for a wide energy range from a few keV to MeV.

Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) are very promising semiconductor materials for Xray and gamma ray detection. The high atomic numbers of the materials (ZCd=48, ZTe=52) provide a high quantum efficiency in comparison with Si. The larger band-gap energy (Eg#1.5 eV, compared to Si Eg#1.1 eV) allows the operation of the detector at room temperature. However, up to now, a considerable amount of charge loss in these detectors resulted in a reduced energy resolution. Recently, significant technological advancements have been achieved to improve the spectral properties and time resolution, based on the advances in the production of crystals and in the design of electrodes and digital readout electronics.

Within ASTRA we will develop a versatile advanced detector system, from sensors and read-out electronics, to DAQ and controls, namely compact large-area CdTe and CdZnTe detectors to perform high precision photon energy measurements from 10-100 keV and up to the MeV range, respectively. It will also be possible to design pixelated readout for imaging measurements.

Precision challenge ASTRA will deal with many challenges in hadron physics: precision X ray spectroscopy for exotic atoms (going from kaonic helium to heavier kaonic atoms or different type of exotic atoms, like sigmonium atoms or protonium); precision measurement of the charged kaon mass; precision measurements in hypernuclear spectroscopy. Other type of precision experiments could also greatly benefit, for example: precision spectroscopy for quantum mechanics studies via hadron physics (violation of the Pauli exclusion principle and signals coming from collapse of wave function), nuclear precision spectroscopy and imaging.

Among the possible future applications of these detector systems in the field of hadron physics we mention a first measurement of the 1s level (energy range around 30 keV) of kaonic helium, but also the possibility to go to heavier kaonic (or other hadronic-type) exotic atoms (energies of hundreds of keV). Such measurements are important to make progress in understanding the Quantum Chromo Dynamics in non-perturbative regime in the strangeness sector, in particular the mechanism of chiral symmetry breaking, having an impact going from particle and nuclear physics to astrophysics.

Without the ASTRA detectors these measurements are either impossible to be performed or very much limited in the precision which could be reached.

Application challenge: the ASTRA detector systems will have applications in many sectors beyond hadron physics, like high-rate, high-resolution spectroscopy with synchrotron light; nuclear medicine (gamma cameras, PET); material science; biology; astrophysics measurements; positron annihilation spectroscopy in material research and inspection.