Frank
Laboratory
of Neutron Physics

Investigations of violations of fundamental symmetries in neutron-nucleus interactions and related data

{loadmoduleid 1076} {loadmoduleid 1054} {loadmoduleid 956} Measurement of TRI and ROT effects for gamma-rays and neutrons in the fission of uranium by polarized neutrons; Measurement of yields and angular correlations of light charged particles in ternary and quaternary fission of 252Cf using Timepix detectors; Determination of characteristics of excitation levels of nuclei in the (n, 2n) and (n, n'γ) reactions with neutrons with an energy of 14 MeV; Measurements of angular and energy distributions of prompt fission neutrons (PFN) in 235U(n,f) and 239Pu(n,f) reactions in the resonance region using a position-sensitive twin ionization chamber and 32 scintillation counters; Determination of model concepts of modern values of the level density and radiation widths of nuclei of various shapes and types in the capture of slow neutrons; Carrying out an experiment to search for a singlet deuteron; Measurement of fast neutron cross sections for 6Li(n,α) 3H and 91Zr(n,α) 88Sr reactions. A series of works on measuring the rotation effect (ROT-effect) of a fissile nucleus in the angular distributions of prompt γ-quanta has been carried out. This effect is expressed as a shift in the anisotropic angular distribution of γ-quanta (Figure 1) emitted using excited fission fragments with some small angle δθ towards the fission axis in the case of reverse direction of neutron beam polarization. {loadmoduleid 957} In fact, it is not the angular distribution of γ-quanta that shifts using the angle δθ, but the fission axis shifts relative to the initial direction of the deformation axis of the fissile nucleus, i.e. the coordinate axis shifts and the angular distribution of γ-quanta is registered relative to it (Figure 2). {loadmoduleid 958} Since the fissile nucleus rotates at the moment of rupture, the fragment trajectories, being rectilinear without nucleus rotation, become hyperbolic that results in a deviation of the fission axis from the initial direction of the fissile nucleus deformation axis. In the experiment, it occurs as an asymmetry of counting of signal coincidences from gamma-quantum detectors and detectors of fragments with respect to the direction of the neutron beam polarization (Figure 3). The latter also determines the direction of the fissile nucleus polarization and consequently, the direction of its rotation. {loadmoduleid 959} The asymmetry of coincidence counting is determined by the ratio:     D(θ) = [N+(θ) - N−(θ)]/ [N+(θ) + N−(θ)].                                           (1) Here, N+(θ) and N−(θ) are the number of coincidences of the signals from gamma-quantum detectors and detectors of fragments (Figure 3), measured at two opposite directions of neutron beam polarization. Gamma-quantum detectors and detectors of fragments are positioned at an angle θ to each other in the plane orthogonal to the axis of the longitudinally polarized neutron beam. {loadmoduleid 960} It can be shown that   D(θ) = δθ ∙ F'(θ)/F(θ),                                                                         (2) F(θ) is a function describing the angular distribution of γ-quanta and F'(θ) is its derivative in the average position of the γ-quantum detector positioned at an angle θ. Thus, by measuring the asymmetry and determining the angular distribution function of γ-quanta, one can determine the angle to which the fragment trajectory is shifted and consequently, the angular velocity and rotation direction of the fissile nucleus (Table 1). {loadmoduleid 961} In total, 3 series of experiments have been carried out, differing from each other in the energy of polarized neutrons, the neutron polarization method, detectors of fission fragments and their positioning, as well as the data acquisition and processing system. All measurements were carried out at the research neutron source Heinz Mayer-Leibniz (the FRM II reactor) at the Technical University of Munich in Garching (Germany). 

Investigation of the fundamental properties of the neutron, UCN physics

Applied research

Development of the IREN facility & it`s experimental infrastructure

Modernization of EG-5 accelerator

TANGRA

Investigation of cosmic matter using nuclear physics methods

Condensed Matter Physics and Materials Science

Physics of Nanosystems and Nanoscale Phenomena

Physics of Complex Liquids and Polymers

Biophysics and Pharmacology

Applied Research and Engineering Sciences

Instrument development program for the IBR-2 spectrometers

Raman spectroscopy

Development of the spectrometers complex