Leader: Daniyar Berikov
Work phone number: +7 (496) 216-36-83
Work E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Scientific problem:
The ROT (fission axis rotation) effect is a subtle but fundamentally significant phenomenon in nuclear fission, manifesting as an asymmetry in the angular distribution of prompt gamma rays relative to the spin of the fissile nucleus. It reflects the underlying dynamics at the scission point, including the mechanisms of spin generation and alignment in fission fragments. Understanding this effect is crucial for refining nuclear fission theory and improving our prototypes of angular momentum transfer during the scission. Recent experiments, including those carried out by our research group, have provided key data on the ROT-effect in the fission of ²³⁵U using polarized neutrons, particularly, at cold and resonance neutron energies (0.06 and 0.27 eV). For the first time, the rotation angle of the fission axis has been estimated for cold neutrons and for the first isolated resonance at 0.27 eV, with the results showing that the ROT asymmetry decreases significantly near the resonance. It confirms theoretical predictions based on the partial cross-sections for J = 3 and J = 4 states and the corresponding K-channel contributions. These results are relevant for testing nuclear prototypes and enhancing our understanding of the fission process as a whole. Furthermore, there is more evidence that the difference in rotation angles between binary and ternary fission may be the key to a deeper understanding of the fission mechanism. Scheduled future measurements, particularly, at the 1.14 eV resonance, are expected to provide critical correlations between rotation angles and fragment properties, possibly resulting in to more accurate prototypes of spin dynamics in fission.
Objective:
To study the ROT-effect in binary fission of ²³⁵U by developing a new experimental setup at the IBR-2 reactor, enabling simultaneous measurement of prompt gamma and neutron angular distributions, reconstruction of fission fragment trajectories, and determination of rotation angles under various neutron energies, including resonances.
Tasks:
1. Design, construct, and calibrate a new experimental setup for simultaneous detection of prompt gamma-rays and neutrons.
2. Implementation of fission experiments with thick, opaque targets, measuring angular distributions of gamma-rays and neutrons.
3. Development and validation of a novel technique for reconstructing fission fragment trajectories using prompt neutron angular anisotropy.
4. Analysis of experimental data to quantify the ROT-effect and to estimate rotation angles at different neutron energies (e.g., 0.06, 0.27, and 1.14 eV).
5. Comparing results with the current theoretical predictions based on partial cross-sections and spin alignment (K-channel analysis).
6. Developing and refining theoretical or phenomenological prototypes to describe the observed ROT-asymmetry and spin generation mechanisms in binary fission.
7. Investigation of differences in ROT behavior between binary and ternary fission modes (if experimental data allows).
8. Preparation and submission of results for peer-reviewed publication and presenting the obtained data at scientific conferences.
Research facilities:
The paper will be completed under the project “Investigations of neutron nuclear interactions and properties of the neutron” at the beamline 1 of IBR-2. Using exteral sources as CSNS is also possible.