At PAC meetings

Reports with new results, proposals and discussions

On 22-23 January, the 62nd meeting of the Programme Advisory Committee for Nuclear Physics was held. The meeting began with opening remarks and a message on the implementation of the recommendations of the previous session that were presented by Chair of the Committee Valery Nesvizhevsky.

Valery Nesvizhevsky and Mikhail Itkis

Afterwards, Advisor to JINR Director and FLNR Deputy Scientific Leader Mikhail Itkis made a report on the implementation of the resolution of the 138th session of the Scientific Council (September 2025) and the decisions of the Committee of Plenipotentiary Representatives of the JINR Member States (December 2025).

DLNP Chief Engineer S.L.Yakovenko made a report and a proposal to open a new project "Technological complex of positron annihilation spectroscopy PASTech". He commented on the main points of his report as follows,

"The positron annihilation spectroscopy technique allows the examination of defects in the surface layers of the material. Thanks to it, you can see both the focus of defects and their dimensions. The sensitivity of the technique has not yet been achieved by anything else. The complex has already been developed and has been working with us since 2016. The new project is aimed at replicating the updated compact facility for the Member States and Russian institutions that wish to engage in solid body research. For those that produce new materials, they study their properties, as well as films and all heterogeneous and homogeneous structures.

We focus a mono-beam of low-energy positrons that can be controlled. It allows one to get to the exact place about which we want to receive information. We can scan up to 10 microns of the surface, examine very small structures and that's what microelectronics needs right now. Dimensions are nanometers and fractions of nanometers.

With our project, we try to make technology more commonplace so that it has a mass character. And there is a request for such compact facilities. We are ready to develop them here, as well as to send them to the Member States."

The Committee highlighted that the development of an advanced technological complex for implementing fundamental and applied research of a solid body by techniques of positron annihilation spectroscopy is an essential task. It is recommended to open a new project.

At the meeting, the report "Experiments at the SHE Factory and the status of the GASSOL Separator" was made by Leader of the Group of Gas-Filled Separator of FLNR D.I.Solovev. Next, Head of Sector No.3 of FLNR N.V.Aksenov spoke about "Investigation of the chemical properties of superheavy elements at the SHE Factory". These reports were commented on by Advisor to JINR Director and FLNR Deputy Scientific Leader Mikhail Itkis,

"In the report of Dmitry Solovev, on the one hand, a new device was presented, on the other hand, the desire to break through to shorter-lived superheavy elements, to study their chemical properties. To study chemical properties, you need to deliver a superheavy atom to a measuring device. It takes time. And if it lives only a fraction of a millisecond or a few milliseconds, then you need to come up with a device that will allow you to deliver faster. GASSOL is a new separator that will be able to unite physics and chemistry in the investigation of super-heavy short-lived elements. This is a very advanced report and perhaps, it presents the most advanced idea in the world in this area. How to understand the chemical properties of superheavy nuclei, where the periodic table ends or does not end? This is one of the greatest questions.

Dmitry Solovev is Leader of the Group for developing a separator. Currently, almost everything is ready. In February, this device will come here, it will begin to be installed and tested. It is expected that after 2027, experiments will begin on it."

The Programme Advisory Committee emphasized the high importance of preparatory work implemented at the SHE Factory. FLNR Directorate is recommended to focus the main resources on the preparation of experiments on the synthesis of the element 119 in the ⁵⁰Ti + ²⁴⁹Bk reaction.

"The two reports are intertwined. Nikolay Aksenov is responsible for chemistry," M.G.Itkis continued. "The first experiments were implemented on an old U-400 accelerator. Today, thanks to the SHE Factory, it is possible to obtain dozens of atoms and to more seriously study the relativistic effects and to generally more deeply understand the chemical properties of superheavy atoms. This is work that requires statistics and installation. The installation is being prepared, as reported by Solovev, later, there are chemical detectors. And then it is necessary to provide good intensity and the SHE Factory allows it, it produces much more super-heavy elements than on our previous ones and in general, on all facilities in the world. This is what the factory was built for and it gives this result. Therefore, these areas of research are promising."

Head of Sector of Weak Interactions of DLNP M.V.Shirchenko presented a report on the current status of the DANSS experiment on registering reactor antineutrinos implemented under the core of the VVER 1000 power reactor of the Kalinin NPP - "Status and modernization of the DANSS detector". The experiment accumulated unique data over a long time with record statistics that allowed obtaining updated restrictions on the parameters of oscillations of reactor antineutrinos into sterile states at short distances. The long-term stability of the DANSS detector has also been confirmed, providing monitoring of the thermal power of the nuclear reactor with an accuracy of ~ 1% at weekly intervals. It has been shown that the antineutrine technique provides accuracy comparable to traditional techniques for estimating power, while being independent and completely non-invasive. On the basis of spectral analysis of antineutrine data, the reconstruction of the time evolution of the shares of the main fissile isotopes of nuclear fuel (²³⁵U and ²³⁹Pu) was implemented that shows the possibility of extracting data about the composition of the fuel directly from antineutrine measurements and emphasizes the applied potential of the experiment.

Further development of the experiment is the DANSS detector modernization programme, aimed at increasing sensitivity, the accumulated statistics and reducing the dominant systematic uncertainties. It is recommended to continue work on the development of the DANSS detector. The scheduled programme of its modernization was supported with high priority.

The report "Status of experiments on double beta decay" was delivered by Head of Sector of Nuclear Radiation Spectrometry of DLNP A.V.Lubashevsky. Neutrinoless double beta decay experiments are a good way to find physics beyond the Standard Model. The observation of neutrinoless double beta decay would allow the neutrino to be identified as a Majorana particle and to provide information on the significance of the neutrino mass. JINR is actively involved in several leading world experiments, such as LEGEND, SuperNEMO and others. The Committee emphasized the scientific significance of research on double beta decay and recommended further participation in all the mentioned experiments with an emphasis on the development of the JINR material base.

Two scientific reports were given. "Reactions of multi-slope transmissions as a way to the island of stability" presented by Head of Sector No.5 of FLNR A.A.Bogachev. With the help of the CORSET facility, a series of investigations was carried out to study the mass-energy distributions of binary divisor-like reaction fragments. It allowed estimating the probability of nuclear fusion in the range of 80≤Z≤122 depending on the parameters of the input channel in reactions with heavy ions.

For the first time in world practice, registration of three-part events in multinucleon transfer (MNT) reactions has been implemented. MNT reactions, allowing the production of heavy nuclei with controlled excitation energy lower than in conventional fusion reactions, can become a promising way to synthesize new isotopes near the neutron shell N=162 and move towards the island of stability.

The report "Measurement of differential and total neutron scattering cross sections with an energy of 14.1 MeV on carbon nuclei: methodological aspects and results" was presented by a senior researcher at FLNP P.S.Prusachenko. It is dedicated to the investigation of differential and integral sections of elastic and inelastic neutron scattering with an energy of 14.1 MeV on carbon nuclei in the angular range from 13 to 150 degrees. A key feature of this investigation was the use of the labeled neutron technique that allowed directly measuring the flux of fast neutrons falling on the sample and the use of the time-of-flight technique provided a clear separation of the contributions of different scattering channels. This research is of high importance for fundamental calculations and applied modeling of the processes of interaction of neutrons with matter.

Seven speeches were prepared by young scientists from the Dzhelepov Laboratory of Nuclear Problems. All scientific and methodological papers and the reports, as emphasized by the PAC members, were of high quality. The best reports were: "Investigation of galactic neutrino flux using the Baikal-GVD telescope", presented by B. Ulzutuev, "³He-⁴He dissolution refrigerators used to obtain ultra-low temperatures", presented by I.S.Gorodnov and "Development of a new neutrino composite detector COFE (Chemical Optical Fluoride Engineering)", presented by K.V.Antokhina.

The report of B.Ulzutuev is recommended to be delivered at the session of the JINR Scientific Council in February 2026.

The open meeting of the Committee for Nuclear Physics was described by M.G.Itkis, "From my point of view, everything went well, there were reports with new results. The previous meeting was six months ago. In summer, as a rule, many facilities are shut down due to the holiday season and in fact, it was reported what had been done in just four months starting in September. The meeting passed intensely. Our foreign colleagues were present in person. It is impossible not to pay attention to the fact that the participants asked questions, including those who were online. This is a good indicator when they not only sit, but also listen, are interested, start discussions. In this regard, I like the Programme Committee for Nuclear Physics. It always brings together physicists from different laboratories and is very active."

The next meeting of PAC for Nuclear Physics will be held on 18-19 June.

Maria KARPOVA,
photos by Igor LAPENKO