New X-ray Imaging Technique
Uppsala researchers have developed a new imaging technique where they have used the quantum properties of X-rays. The results look promising for further development of methods for imaging proteins in the future.
The researchers have for the first time been able to image the structure of a copper sample by measuring the X-ray fluorescence which arises when the copper atoms in the sample are irradiated. The study was published recently in Physical Review Letters and has also been selected as Editor Viewpoint.
The method of the experiment is based on the same principle as the astronomers Hanbury-Brown and Twiss were using in the 50s, when they determined the size of distant stars. The astronomers managed to determine the size of stars with the help of two telescopes that detected light which came from various parts of the same star and interfered with each other on their way to Earth. This was a groundbreaking experiment which opened the door to quantum optics and gave a better understanding of the quantum nature of light.
In the new study, the Uppsala researchers have in a collaboration with researchers from a number of German institutes used the same principle and the quantum properties of X-rays. Instead of light from the stars, they have used fluorescent light created by irradiating the atoms in a copper sample. This was done with the help of ultrafast and very intense X-ray pulses from the European X-ray Free Electron Laser (EuXFEL) facility in Hamburg.
X-ray fluorescence is created when heavier atoms, such as metal atoms found in many proteins and protein complexes in living matter on Earth, are irradiated with X-rays. The fluorescence can give more information about the local structure and the atoms’ chemical state, which is useful in order to learn more about how important proteins in the body work. This is the first time anyone has examined interference of X-ray fluorescence that comes from independent atomic sources. By measuring the interference, the researchers have been able to image the structure of the sources as an image on an advanced 2D-detector with high resolution and quick response time.
In total, more than 58 million exposures were made in the study. Each image had a weak signal with just a few thousand photons detected per image, and each pixel in such an image may be seen as a mini telescope.
The X-ray fluorescence light is emitted during less than a femtosecond and interference can only take place between sources that almost simultaneously emit light during this extremely short time. By measuring the correlations between the photons, the researchers could obtain information about the position of two independent fluorescent sources on the copper sample.
In the study, the researchers used a copper sample, but the expectation is that the method used in the study can be developed and combined with other methods for X-ray imaging of for example proteins in the future.
Fabian Trost et al., Imaging via Correlation of X-Ray Fluorescence Photons, Phys. Rev. Lett. 130, 173201 – published April 24, 2023. DOI: https://doi.org/10.1103/PhysRevLett.130.173201
Nicusor Timneanu, Senior Lecturer at the Department of Physics and Astronomy, email@example.com.
English translation: Johan Wall