| BY AN UNBEATEN WAY |
V. V. Fedorov
Creation of the first in our country focusing crystal-diffraction Cauchois g-spectrometer (GSK-1) in 1956 [1] by O.I.Sumbaev and P.I.Lukirski (1894-1954) gave rise to the Gatchina scientific school of the diffraction researches and application of the diffraction methods in very different fields of physics (P.I.Lukirski could not see the ready device unfortunately). The event had not passed unnoticed. On March 17, 1956 the Leningrad newspaper "Smena" published the article devoted to young scientist Oleg Sumbaev, who had just finished the hard work started with the academician P.I.Lukirski on creation of the spectrometer. The paper noticed that after that not only the USA but also the USSR would have such a crystal-diffraction technique.
Young Oleg Sumbaev at the page of "Smena" newspaper under the title: "By an unbeaten way".
Using this spectrometer mounted in the room near the reactor WWR-M hall, the first experimental results was obtained in 1961 [2], concerning the Mossbauer effect in tungsten isotopes (O.I.Sumbaev, A.I.Smirnov, V.S.Zykov). It was one of the first works carried out at the WWR-M reactor started up on December 1959. At present, the spectrometer GSK-1 is still successfully used for measurements of a small energy displacements of the X-ray lines.
Now the scientific school has a wide experience in the creation of unique crystal diffraction devices and in the works at them. The essential contribution was made into development of the diffraction physics of X-rays, electrons and neutrons in the perfect crystals. A number of the discovered new effects have found the wide applications in the various fields: from the physics and chemistry of condensed matter to the nuclear and elementary particle physics.
The advanced theory of elastic quasimosaicity of crystals and the theory of diffraction in elastically deformed crystals developed by O.I.Sumbaev in 1957 (see [3-7]) has given a unique opportunity of adjusting within the limits of several orders a luminosity and resolution of the devices (by a choice of the appropriate crystallographic planes, the thickness and the crystal bending radius) and has got the world recognition. This allows to create the spectrometers with optimum parameters for the work.
Recently the high resolution X-ray and gamma-spectrometers have found a wide application in nuclear spectroscopy and spectroscopy of hadronic atoms. The high luminosity X-ray spectrometers do that in spectroscopy of the small energy shifts (chemical, isotopic and hyperfine) of X-ray lines (the absolute accuracy of shift measurements is of about 1 millielectronvolt (meV), which corresponds to the relative one of 10-7).
X-ray (Fig. 1) and gamma spectrometers with the optimized resolution and luminosity are used now in atomic and molecular physics for study chemical bond, isomorphic phase transitions in crystals, the features of structure of the high temperature super conductors (HTSC) etc. They are also used in the nuclear spectroscopy with the highest resolution (an example of measured g - line can be seen in Fig. 2); for determination of the charge radii and the multipole moments of nuclei by measuring the isotopic displacements and the hyper-fine structure shifts of the X-ray lines, accompanying internal conversion; for precise determination of the masses of p -,K - mesons and S - hyperon, and also for studying the strong hadron nucleus interactions in hadronic atoms by measurements of the X-ray spectra of exotic atoms.
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Fig. 1. The scheme of the two-meter Cauchois crystal diffraction spectrometer (GSK-1) for measuring small energy shifts of the X-ray lines
Fig. 2. The instrumental shape of the g-line 176.89 keV, measured with a record high ren in the 5-th order of reflection at GSK-2m
The scheme of crystal diffraction spectrometer is presented in Fig. 1. A fluorescent X-ray radiation of one of the sources S1 - S4, excited by the initial radiation with continuous spectrum of an X-ray tube (or of a radioactive source), falls through the collimator on the quartz single crystal plate bent with the radius of 2 m. Diffracted X-rays are focused in a narrow line at 2 m distance from the crystal and through a reception slit of 0.3 mm wide reach a scintillation detector NaJ(Tl).Energy selected by the device is determined by position of the reception slit of the detector and by orientation of the crystal reflecting planes.
The crystal, clamped between convex and concave mirrors, is fixed on a table having the vertical axis. The axis is connected with the meter lever, the end of which through a sapphire plate and the steel tempered ball sets against the micrometric screw that is rotating by electric motor through a worm reducer (R), so that the one revolution of the motor rotation corresponds to the 5 microns movement of the micrometric screw and, accordingly, to 1 angular second of the crystal turn. Turning a crystal by a given angle, one can investigate any part of an X-ray line passed through the slit.
From 1986 in our laboratory the new direction of the scientific activity has arisen. We have started the researches on diffraction of neutrons both in flat, and in the bent perfect single crystals. The method of measurement of a pendulum picture has been developed for experiment on dynamical diffraction of neutrons in such crystals. When using the diffraction of neutrons in a slightly bent crystal the gravitational effect has been measured for the first time through the change of the pendulum picture contrast resulted from an over-turn of the experimental setup.
The presence of a strong electric field, affecting a neutron under diffraction in a noncentrosymmetric crystal, is theoretically predicted. This field is first measured, using dynamical diffraction of the polarized neutrons in an alpha-quartz crystal without centre of symmetry. The obtained experimental field value has coincided with the theoretical one. A new experiment on a search for the neutron electric dipole moment (EDM) is proposed and developed in details for neutron diffraction in noncentrosymmetric crystals at a level of accuracy 10-26 e·cm. Now the first experimental results are obtained at the created pilot setup.
The researches of the charged particle channelling in bent single crystals were carried out. The phenomenon of the volume capture of particles in a channelling mode in the bent crystal was predicted and was confirmed experimentally. For the registration and the selection of channelling particles the unique installation was created that combined the bent silicon crystal with a few semi conductor detectors realized on the same crystal. Using the volume capture effect and the installation, it has turned out to be possible to carry out an experiment on the determination of magnetic moment of S+-hyperon, by measuring the spin rotation angle after channelling in the bent single crystal. As well the new feasibility of focusing of the high energy channelling particles by the bent single crystal with a special face cut was theoretically shown and proved experimentally. This phenomenon opens new opportunity to control beams of the high-energy particles and therefore these investigations have attracted a wide interest in a number of the world accelerator centres.
The researches of the charged particle channelling in bent single crystals were carried out. The phenomenon of the volume capture of particles in a channelling mode in the bent crystal was predicted and was confirmed experimentally. For the registration and the selection of channelling particles the unique installation was created that combined the bent silicon crystal with a few semi conductor detectors realized on the same crystal. Using the volume capture effect and the installation, it has turned out to be possible to carry out an experiment on the determination of magnetic moment of S+-hyperon, by measuring the spin rotation angle after channelling in the bent single crystal. As well the new feasibility of focusing of the high energy channelling particles by the bent single crystal with a special face cut was theoretically shown and proved experimentally. This phenomenon opens new opportunity to control beams of the high-energy particles and therefore these investigations have attracted a wide interest in a number of the world accelerator centres.