Recent developments in the use of X-rays

The discovery of X-rays. X-rays were discovered in 1895 by German physicist Wilhelm Roentgen. Röntgen was able to observe, to notice the new, where many scientists before him had found nothing remarkable. This special gift to help him make a remarkable discovery.

Wilhelm Roentgen (1845-1923) - German physicist, discovered in 1895, short-wave electromagnetic radiation - X-rays. The discovery of X-rays had an enormous influence on the subsequent development of physics, in particular, led to the discovery of radioactivity. He was the first Nobel Prize in Physics was awarded. It contributed to the rapid spread of the practical application of their discoveries in medicine. The design of the first X-ray tube he created for X-rays is almost unchanged to date.

At the end of the XIX century. physicists drew everyone's attention the gas discharge at low pressure. Under these conditions, the gas discharge tube to create threads very fast electrons. At that time they were called cathode rays. The nature of these rays have not been established with certainty. It was known only that they originate at the cathode tube.

Having been engaged in the study of cathode rays. X-rays soon noticed that near the discharge tube plate provided illuminated even when she was wrapped in black paper. After that he was able to observe another very struck his phenomenon. Paper screen, moistened with a solution of barium platinosinerodistogo, began to glow, if they discharge tube was wrapped. Moreover, when the X-ray was holding his hand between the tube and the screen, the screen could be seen the dark shadow of bones on a background of lighter shapes throughout the hand.

Scientists realized that when the discharge tube there is some previously unknown highly penetrating radiation. He called it the X-rays. The term "X-rays" firmly established later for this radiation.

Roentgen discovered that new radiation appearing at the place where the cathode rays (electron flows fast) faced with the glass tube wall. At this point, the glass glowed greenish light.

Subsequent experiments showed that X-rays are produced when braking of fast electrons any obstacle, such as metal electrodes.

X-ray properties. Rays open Roentgen, acting on a photographic plate, cause ionization of the air, but not noticeably reflected by any substances and the refractive experienced. The electromagnetic field had no effect on the direction of propagation.

As soon as it has been suggested that X-rays - electromagnetic waves, which are emitted during heavy braking of electrons. Most of the penetrating power of X-rays and their other characteristics were associated with short wavelength. According to this hypothesis requires proof, and evidence was obtained 15 years after Roentgen's death.

X-ray diffraction. If X-rays are electromagnetic waves, it should detect the diffraction - a phenomenon common to all types of waves. First, X-rays are passed through a very narrow gap in the lead plates, but nothing like it was not possible to detect diffraction.

New sources of SI - SI sources 4th generation are huge engineering structures 1). For example, the perimeter of the largest to date in Europe, the storage ring of the 3rd generation of ESRF in Grenoble is 844 meters and the storage rings and APS SPring8 more.

SI sources are always shared installations, where different organizations can subscribe to temporarily or permanently separate synchrotron radiation channel for its work, or to order the execution of research personnel source.

2.9. New sources of SI - SI 4th ​​generation sources The acquired research experience with the use of the broad opportunities provided by SI sources, pushes to increase the requirements for these sources. In particular, the desire to be investigated using X-ray increasingly smaller volumes of matter (sizes on the order of several nanometers), requires high-brightness microbeams and to study structural transformations in real-time chemical reactions it is desirable to have a duration of about 100 femtoseconds pulses. Over tridtsatilenie efforts of scientists and engineers for the design and construction of increasingly sophisticated storage rings led to the fact that their performance in the SI 3rd generation sources have reached their physical limits, both in size and brightness of the light source and by its temporal structure. For example, the diameter of the electron beam in a storage ring at ESRF 7 GeV and 200 mA is 50 microns, and further can not be reduced due to the physical principles, and hence can further improve the brightness and SI.

Performance limits are radiation sources based on storage rings naturally concluded in the very principle of their action as photon radiation sources. They can not be overcome by any further technical improvements. These limits are parameters associated with the condition of accumulation of accelerated particles (DC), in which the particles in the ring should be accumulated in stable equilibrium orbits and properties of clots must be consistent with perturbations of energy and momentum that arise in the emission of SI, the properties of the RF accelerating system, inter-particle effects scattering in the beam (Touschek effect), and errors in the system, turning and focusing magnets.

All these disturbances lead to the connection between the horizontal and vertical dimensions of the beam of particles in orbit. These perturbations are properties of each specific storage ring and determined by the structure of its magnetic and electro-optical elements. In turn, the structure of the storage ring is constructed as a compromise between the initial emittance packages loaded particles and the structure of their balanced clots, which is typically achieved over many thousands of revolutions around the ring and is characterized by a length of a few milliseconds. Although the particles in equilibrium compression packs storage ring provides excellent stability, it leads to the fact that the parameters balanced bunches accumulated unrelated to parameters originally injected packet particles which, in principle, may have a length and several orders less. Therefore, if the storage ring to inject fine particles generated by packets of emittance and a length less than those that are characteristic of the structure of the ring, in the process of moving to 1) certain characteristics of synchrotron radiation sources listed at the end of this book in the Table. 6.9.