Laboratory of Neutron Physics

EXPERIMENTAL SCIENTIFIC FACILITY

The scientific and experimental work of the Laboratory of Neutron Physics is mainly carried out using neutron beams of the multifunctional WWR-K research reactor. This reactor is a multipurpose pool-type water-water reactor with a stationary neutron flux. In basin reactors, nuclear fission in the core is carried out mainly by slow (thermal) neutrons. Therefore, it belongs to the class of thermal neutron reactors.

Currently, there are 3 scientific instruments operating on the basis of the LNP:

Instrument of neutron radiography and tomography TITAN

TITAN – experimental station of neutron radiography and tomography designed for diagnostics and visualization of the internal structure of dimensional objects. It is located on the 1st horizontal channel of the WWR-K research reactor. The main components of the TITAN installation are neutron filters, an aperture system, a system of collimators for the formation of a thermal neutron beam, a goniometer, neutron detection and data collection system. The following operating modes of the installation are implemented:

Radiography – method of recording shadow projections of an object illuminated by a neutron beam. The contrast of the image is due to variations in density and/or chemical composition and can be enhanced by changing the wavelength of the neutron beam.

Tomography – a method for reconstructing the three-dimensional distribution of neutron-optical density over an object by mathematically processing a set of digitized shadow projections obtained at various angular positions of the object.

Rapid radiography/tomography – a method for recording neutron projections with short exposures for fast and dynamic processes.

Neutron Reflectometry Instrument

Neutron reflectometry is a neutron diffraction technique used to measure the structure of thin films and is a complementary method for X—ray reflectometry. This method provides valuable information in a wide range of scientific and technological applications, including chemical aggregation, adsorption of polymers and surfactants, structure of thin-film magnetic systems, biological membranes, etc. When implementing this method, a highly collimated neutron beam falls on a flat surface of the sample and the intensity of the reflected radiation is measured depending on the angle or wavelength of the neutrons. The precise shape of the reflectivity profile provides detailed information about the surface structure, including the thickness, density and roughness of any thin films deposited on the substrate.

This polarized neutron reflectometer at the WWR-K reactor is equipped with a two-crystal monochromator for the possibility of varying the wavelength (energy) of neutrons and from leaving the line of sight of the beam relative to the reactor core, with the geometry of the installation unchanged.

Main areas of research

- Study of the structure of thin films on a solid substrate.

- Non-polarized neutron beam mode: restoration of parameters of effective layer thickness, roughness of boundaries between layers and free surface, determination of neutron-optical density of layer materials.

- Polarized neutron beam mode: assessment of the magnetic properties of the structure of layers on the surface of the substrate, type of magnetic ordering of layers in an external magnetic field.

X-ray Radiography and Tomography Instrument

X-ray microtomography has become a well-established non-destructive testing method. The high penetration depth of X-rays into many materials makes it possible to reconstruct volumetric information from a series of 2D projection images, revealing the internal structure of a sample. This makes this method attractive when sample integrity is critical, for example. in biomedical imaging, archaeometry, paleontology, industrial quality control, and materials science. Also, the difference in the nature of the interaction of X-ray and neutron radiation with matter can provide useful and complementary information about the objects of study.

This high-resolution X-ray tomograph is designed to analyze the internal structures of various samples, take measurements and visualize the three-dimensional volume of the test object. The microtomograph allows you to control the magnification factor and rotate the test object, and carry out tomographic reconstruction of up to 7200 projections.

CURRENT PROJECTS OF LNP

Mega-Science project “High-intensity UCN source based on the WWR-K reactor»

Due to their unique feature, ultracold neutrons (UCNs) are used as a sensitive tool in fundamental physics experiments where high-precision measurements are required. Various UCN measurements are specifically aimed at solving unanswered questions in fundamental physics, astrophysics and cosmology. These include testing fundamental theories such as searching for the electric dipole moment of the neutron, measuring the neutron lifetime and searching for new types of interactions at short distances, searching for neutron-antineutron oscillations, etc.

However, the solution to these problems is limited by the intensity of the UCN source, so the development and creation of a high-intensity UCN source is extremely important, which will make measurements more complete and minimize statistical errors. In this regard, it is proposed to develop a high-intensity UCN source in the thermal column of the WWR-K research reactor.

The thermal column of the WWR-K reactor meets all the requirements for creating a UCN source with a record UCN density for fundamental research. The large diameter (1 meter) of the thermal column allows the placement of a 10 cm thick lead screen to reduce the thermal load; graphite at room temperature slows down neutrons to the thermal energy range; a low temperature converter of 19 K will produce cold neutrons, and superfluid helium at 0.8–1.25 K will convert cold neutrons to ultracold neutrons. The calculated volume density of UCN in a source chamber with a volume of 35 l is about 1.6 * 10⁵ n/cm³ at a helium temperature of 0.8 K, which is more than 100 times higher than the maximum achievable UCN density in other neutron sources.

Project “Neutron powder diffractometer for studying the crystalline and magnetic structure of materials»

The most direct and informative method for studying the crystal structure and magnetic ordering in materials is neutron diffraction. Functional materials have physical and chemical properties that change when external conditions or environmental parameters change, and the setting or change of these properties must be predictable and controllable. The development of such materials is the main task of 21st century research in many fields of science and technology, and the design and application of modern diagnostic methods for functional materials is an integral part of this activity.

One of the reliable methods for diagnosing functional materials is the neutron diffraction method. Compared to other methods, this method has a number of important advantages. Thus, neutron diffraction makes it possible to study the structure of crystals containing light elements or elements with similar atomic numbers, which in many cases is difficult to do using X-ray structural analysis. The presence of a magnetic moment in a neutron makes it possible to study the magnetic structure of substances. This makes it possible to establish the presence and type of magnetic structure - the ordered orientation of the magnetic moments of atoms relative to each other and crystallographic axes, the magnitude of the magnetic moment of the atom, the temperature and nature of magnetic transitions. Neutronography is successfully used to solve problems in modern industry: hydrogen energy, nanotechnology, production of information storage devices, microelectronics, pharmaceuticals.

The optimal combination of the neutron beam of channel 5 at the WWR-K research reactor, the focusing unit of monochromators, and the unique multi-detector system of the diffractometer being developed will make it possible to obtain high-quality data on the crystalline and magnetic structure of various compounds.

This project proposes to create a neutron powder diffractometer on the 5th channel of the WWR-K reactor, equipped with a vertically focusing crystal monochromator and a detector with a wide coverage angle (banana type).