The first tests of a Compton X-ray microscope prototype that scientists of Tomsk State University and DESY (German National Synchrotron Center, Hamburg) are working on have been carried out in Germany. According to the researchers, the resulting images have greater contrast compared to images in transmitted x-rays.
Since 2018, TSU and DESY scientists have been developing a unique research instrument — the Compton X-ray microscope for studying biological objects. The task of TSU scientists is to create sensors based on gallium arsenide compensated with chromium (HR GaAs: Cr). They will be one of the key elements of the microscope, as they will determine the sensitivity and spatial resolution of the instrument.
– At the end of 2018, at DESY, experiments using X-ray radiation (a PETRA P11 beamline) with an energy of 28 keV and a detector, based on the TSU multi-element sensor containing 512 × 768 pixels, were carried out. They were dedicated to image formation using the registration of backscattering (Compton) X-rays. It is established that the obtained images have greater contrast compared to images in transmitted X-ray radiation, - said Anton Tyazhev, a researcher at the TSU Laboratory of the Functional Electronics.
Also during 2018, TSU radiophysicists optimized HR GaAs: Cr sensors specifically for the tasks of an X-ray microscope. For example, scientists have developed a technology for creating a X-ray transparent metal contact of a sensor to reduce X-ray absorption - now the contact passes at least 98% of radiation in the range of 10 keV and above. This is necessary to increase the sensitivity of the microscope by registering a wider spectrum of scattered radiation.
In addition, Tomsk scientists optimized the technology of creating pixel contacts of matrix sensors, for example, reduced the diameter of the contact metallization window (under-bump metallization). Prior to this, the minimum size of UBM was 35 micrometers, now it is 25 micrometers. In this regard, the percentage of defective pixels on the sensor will decrease, and the detectors will become of higher quality.
The microscope developed by TSU and DESY is designed to study cellular structures, tissues, and protein molecules. Modern electron microscopes quickly destroy the object due to electron bombardment. In the new Compton microscope, the effect is weaker, the destruction will be slower, and this will increase the study time. This work was financially supported by grants from RSF # 18-44-06001 (TSU, Russia) and HRSF-0004 (DESY, Germany); a microscope prototype will be created by 2021.