At PAC meetings

Results, plans, new ideas

The 58th meeting of the Programme Advisory Committee for Nuclear Physics, held on 29-30 January in a mixed format at the JINR Conference Centre, concluded the series of winter meetings of the PAC 2024.

Chairman of the PAC for Nuclear Physics V.V.Nesvizhevsky presented a report on the implementation of the recommendations of the previous PAC meeting. JINR Vice-Director S.N.Dmitriev informed the PAC about the resolution of the 134th session of the Scientific Council (September 2023) and the decisions of the Committee of Plenipotentiaries of the JINR Member States (November 2023). JINR Chief Scientific Secretary S.N.Nedelko commented on the Seven-Year Plan for the Development of JINR in 2024-2030, adopted at the PAC that includes the main topics and projects for research and development of the JINR infrastructure for this period.

The PAC noted with satisfaction that the recommendations of the previous PAC meeting on JINR research in the field of nuclear physics were accepted by the Scientific Council and the JINR Directorate.

Next, the PAC members proceeded to discuss work plans for scientific research and infrastructure development of JINR laboratories in the field of nuclear physics within the framework of topics and projects for 2024. The PAC listened with interest to the report on the work plan within the framework of the topic "Neutron Nuclear Physics" and its projects for 2024, presented by E.V.Lychagin.

The scientific programme of the topic "Neutron Nuclear Physics" will be implemented within the framework of three projects: two scientific ("Research on the interaction of neutrons with nuclei and neutron properties" and TANGRA) and one scientific and technological ("Modernization of the EG-5 accelerator and its experimental infrastructure").

Within the framework of the project "Research on the interaction of neutrons with nuclei and neutron properties", measurements of angular correlations and gamma quanta yields for already known p-wave resonances in various nuclei, as well as the search for new p-resonances and new effects indicating violation of parity and T-invariance will be resumed. The main work is expected to be carried out at the IREN resonance neutron source.

In 2024, it is expected to study the resonance capture of neutrons on ¹⁷⁶Lu and ¹⁷⁷Lu in the neutron energy range 1-300 eV. The goal of the experiment is to study the impact of Coriolis interaction on the structure of nuclear excited states. The measurements will be carried out at the IREN resonance neutron source and in China at the Spallation Neutron Source (CSNS).

Further research on rare modes of fission (ternary, quadruple and quinary) of ²³³U and ²³⁵U nuclei under the impact of thermal neutrons will be carried out. The measurements are supposed to be implemented at the VVR-K nuclear research reactor (Kazakhstan).

In 2024, the reaction cross sections (n, α) on gas samples of Ar, F, O, Ne will be measured.

The TANGRA project is dedicated to meeting fundamental and applied issues using the tagged neutron technique. The goal of the project includes nuclear reactions occurring under the impact of neutrons with an energy of about 14 MeV.

Main research areas in 2024:

• reaction cross sections (n, xγ) on 22 elements will be measured. This information is necessary for elemental analysis, Monte Carlo simulation of nuclear facilities and verification of theoretical calculations;
• the angular correlations of neutrons and gamma quanta in the inelastic scattering of neutrons on carbon will be measured. Experiments to study correlations (n, n' γ) are important for understanding the mechanism of reactions (n, n').

Within the framework of the project "Modernization of the EG-5 accelerator and its experimental infrastructure," the high-voltage system of the EG-5 facility will be replaced, the main result of which will be an increase in the ion beam current from 2-3 to 100-250 mA while maintaining its energy and spatial stability.

PAC members noted the promise of the proposed scientific programme within the framework of the topic "Neutron Nuclear Physics" and its projects.

PAC members listened with interest to the report on plans for research on heavy ion beams at FLNR for 2024, presented by FLNR Director S.I.Sidorchuk. The scientific programme will be implemented within the framework of two projects: "Investigation of heavy and superheavy elements" and "Light exotic nuclei at the boundaries of nucleon stability."

For the project "Research of heavy and superheavy elements" at the SHE Factory, the basic focus will be on meeting the following issues:

• to carry out the ⁵⁴Cr+²³⁸U experiment in future that is extremely important for preparing the synthesis of new superheavy elements with numbers 119 and 120;
• to prepare and carry out the first experiments on spectroscopy of isotopes of superheavy elements produced in the reaction ⁴⁸Ca+²⁴²Pu. The experiment will be implemented on a GRAND separator and a GABRIELA-2 detection unit with five clover-type detectors made of ultra-pure germanium. The observation of alpha decay of the even-even nucleus ²⁸⁶Fl into the first excited state ²⁸²Cn that may be of a rotational nature, is expected.

At the CORSET facility, the main focus will be on studying the dynamics of multinucleon transfer reactions with the production of two or more heavy products in the output channel.

The main task of the project "Light exotic nuclei at the boundaries of nucleon stability" in 2024 will be the preparation and implementation of the first experiments to study the structure of light nuclei positioned near the boundaries of nucleon stability on the AKULINA and AKULINA-2 fragment separators of the upgraded U-400M accelerator.

In 2024, research will focus on studying the structure of heavy helium isotopes ^6,7He, as well as the reaction mechanisms resulting in the production of unbound exotic systems such as 4n. In particular, elastic and inelastic scattering of ⁶He on the ⁴He nucleus will be studied over a wide range of angles that includes back scattering corresponding to the transfer of two neutrons.

Within the framework of the research of the mechanisms of quasi-binary transfer reactions with the production of unbound states like ⁷H and 4n, experiments will be carried out to study the ⁵H and 2n states in the reactions ²Н(⁶Не,⁶Li)2n and ²Н(⁶Не,³Не)⁵Н.

The PAC supported scientific and technological programmes for 2024 on the topic "Synthesis and properties of superheavy elements, the structure of nuclei at the boundaries of nucleon stability" and further work on the projects "Research of heavy and superheavy elements" and "Light exotic nuclei at the boundaries of nucleon stability."

The PAC members listened with interest to the report on the development of the FLNR accelerator and experimental base, presented by Head of the Department of FLNR V.A.Semin. The basic efforts within the project in 2024 will be aimed at:

• providing beams with the required characteristics for the implementation of the FLNR experimental research programme at the operating accelerator complexes DC-280 (SHE Factory) and U-400;
• completion of modernization and commissioning work on the U-400M accelerator. Ensuring the implementation of the first experiments on beams of radioactive nuclei;
• completion of the development of the DC 140 complex for implementing applied research on heavy ion beams.

Within the framework of the project "Development of the U-400R accelerator complex" technological development of the components of the modernized U-400R accelerator, the construction of a new experimental hall, as well as work on projects for new experimental facilities to be positioned in this experimental hall will be carried out in future. The shutdown of the U-400 accelerator and the start of its modernization are scheduled for the second half of 2024.

The project "Development of experimental facilities for studying the chemical and physical properties of superheavy elements" is aimed at developing a multi-reflection time-of-flight mass spectrometer and GASSOL preseparator based on a gas-filled superconducting solenoid. In 2024, the development of working design documentation for the mass spectrometer is expected, as well as the completion of production and delivery to JINR of the GASSOL preseparator.

The PAC recommended approving the work programme for 2024 for the development of the FLNR accelerator and experimental base within the framework of the large JINR research infrastructure "Development of the FLNR accelerator complex and experimental facilities (DRIBs-III)".

PAC members listened with interest to the report on the scientific programme in nuclear physics at DLNP, presented by Director E.A.Yakushev. Nuclear physics research areas in the laboratory include both classical spectrometry of radioactive isotopes and the investigation of various rare phenomena using nuclear physics techniques. The section "Nuclear Physics" of the JINR Topical Plan includes one of the main scientific topics of DLNP - "Non-accelerator neutrino physics and astrophysics" that is aimed at searching for evidence of the occurrence of New Physics beyond the Standard Model. The main areas of the topic are the research of double beta decay using various calorimetric and track-calorimetric techniques, the investigation of the properties of neutrinos from various sources, the search for dark matter, etc. A significant part of the laboratory's scientific programme is dedicated to the research of processes inside the core of a nuclear reactor using neutrinos. Three projects are currently implemented within the framework of the topic: "Nuclear spectrometry for the search and investigation of rare phenomena", "Short-baseline research of reactor neutrinos" and "Radiochemistry and spectroscopy for astrophysics and nuclear medicine". The projects complement each other because their implementation is united by common approaches and resources.

A significant part of the laboratory staff involved in the nuclear physics programme is engaged in the construction and putting the Baikal Deep-Sea Neutrino Telescope (Baikal-GVD) into operation that belongs to the large research infrastructure of JINR.

In 2024, the laboratory is going to put the two new basic facilities the LINAC-200/800 electron accelerator and a spectrometric cluster working in tandem with it into operation. The laboratory develops experimental techniques and carries out applied research with monochromatic positron beams. A new facility is in the process of being developed - the MSC-230 proton cyclotron for the new scientific and clinical centre for proton therapy.

PAC members highlighted that DLNP uses a wide range of nuclear physics techniques to develop and carry out experiments and to obtain physical results that are at the forefront of modern science.

The PAC recommended further support for the implementation of the DLNP scientific programme in nuclear physics and also emphasized the importance of efforts to improve the experimental base at JINR in future.

PAC members listened with interest to two reports: "On testing T-invariance in the full cross section of the interaction of neutrons with unpolarized nuclei using the polarization-asymmetry theorem," presented by V.R.Skoy and "Investigation of the properties and application of nanodiamond reflectors of low-energy neutrons", presented by A.Yu.Nezvanov. The PAC supports this research.

PAC members heard and discussed nine short reports on new results and projects of young scientists from FLNP in the field of nuclear physics. Three best reports were awarded: "Enhanced targeted extraction of very cold neutrons using a reflector made of diamond nanoparticle powder", presented by A.Yu.Nezvanov, "Accumulation and distribution of chromium, nickel and zinc in root crops and leafy vegetables irrigated with industrial wastewater - a laboratory investigation", presented by A.V.Kravtsova and "Experimental facility for elemental analysis using prompt gamma rays at the IBR-2 reactor", presented by K.Khramko.

The PAC recommended the report of A.Yu.Nezvanov for presentation at the session of the JINR Scientific Council in February 2024.

Evgeny MOLCHANOV