Scientists created the world's first Compton microscope

TSU radiophysicists and scientists from German Electron Synchrotron (DESY) national research center have completed developing and testing the world's first Compton microscope, which makes it possible to research at the subcellular level, that is, to study living, functioning cells without preparation. This device of a new class based on scattered radiation does not destroy the object of study after it is irradiated with an X-ray beam, in contrast to transmission X-ray microscopy.

The main task was to reduce the X-ray dose when reconstructing a three-dimensional image of biological samples with high spatial resolution. The joint development of TSU and colleagues from DESY significantly increases the exposure time in the study of cell structures, tissues, and long protein molecules, which are rapidly destroyed in a transmission X-ray microscope due to the large absorbed dose. In the new device, the impact is weaker, which means that the destruction will be slower. 

A large amount of radiation damages the sample, so it significantly limits the level of image detail. An additional complication is that some of the radiation damage occurs with a dose-dependent delay, making the results difficult to interpret.

- Unlike a transmission X-ray microscope, in a Compton, image formation occurs in scattered X-rays. Only a small part of the X-ray energy is absorbed in the object of study, which leads to a decrease in the rate of degradation of the objects during the experiment, - explained Anton Tyazhev, head of the TSU Laboratory of Ionizing Radiation Detectors.

An increase in the contribution of Compton radiation is achieved by increasing the energy of X-ray quanta to 30-60 keV. And this leads to the need to develop and manufacture a specialized pixel detector based on large-area gallium arsenide matrix sensors. Such sensors became the responsibility of TSU radiophysicists, who have developed a technology for creating an X-ray- transparent metal contact. Now it transmits at least 98% of X-rays in the range of 10 keV and above. This increases the sensitivity of the microscope by recording a wider spectrum of scattered radiation.

- We reduced the diameter of under bump metallization (UBM) from 35 micrometers to 25 micrometers. In this regard, the percentage of defective pixels on the sensor has decreased, and the detectors are better quality, added Anton Tyazhev.

The detectors based on gallium arsenide are a unique development of a team of Tomsk scientists led by TSU professor Oleg Tolbanov. These detectors have no analogs in the world. In addition to the German synchrotron center DESY, they are used at the Large Hadron Collider at CERN and in other leading research centers.