Nuclear Josephson junction.

The Josephson effect is a quantum phenomenon appearing in superconductors.
It consists in the spontaneous flow of electric current, due to tunneling, between the two
superconductors separated by a thin insulator layer. The current flow is induced by
phase difference of wave functions describing superconducting electrons on both
sides of the insulator. This is called the Josephson junction.
The phenomenon occurs in metals as well as in ultracold atomic gases.
Search for the Josephson effect in nuclear systems
have been going on for almost half a century.
Theoretical analysis of recent experiments involving collisions of Nickel-60 and Tin-116
provided strong arguments for creation of the Josephson junction.
Contrary to the previous measurements where
the pair transfer cross section has been investigated, this time the gamma radiation spectrum
was analyzed. It turned out that the spectrum of emitted gamma rays agrees with the theoretical
predictions assuming the formation of the so-called AC Josephson junction.

Piotr Magierski

The Tiniest Superfluid Circuit in Nature

Physics 14, 27 (2021)

DOI:10.1103/Physics.14.27

Predictions for over a thousand of the heaviest atomic nuclei

Physicists from the National Center for Nuclear Research and the University of Zielona Góra have determined and reported extremely important parameters for over 1,300 nuclei, including the nuclei of super-heavy elements, which have not been produced in laboratories so far. These results have just been published in the primary reference journal of nuclear physics: Atomic Data and Nuclear Data Tables.

Scientists in many centers around the world are constantly striving to create and research new elements and their isotopes. The main aim of this international race is to discover the still mysterious forces binding atomic nuclei. The research focuses simultaneously on experimental work using powerful accelerators and detectors, as well as on theoretical calculations to identify the most promising production procedure and propose models that can be verified by experiments. Polish scientists have been specializing in this type of theoretical research for several decades, being world leaders, which is clearly confirmed by the extremely extensive and complete work that has just been presented.

Three Polish scientists: Dr. Piotr Jachimowicz from the University of Zielona Góra and Michał Kowal and Janusz Skalski, professors at the National Center for Nuclear Research (NCBJ) estimated the key parameters for 1,305 heavy and super-heavy nuclei in the atomic number Z from 98 to 126 (and therefore also for elements still undiscovered) and for the number of neutrons N from 134 to 192.

“For our calculations, we used a multidimensional microscopic-macroscopic model that allows us to determine the binding energy of atomic nuclei” – explains Dr. Piotr Jachimowicz from the University of Zielona Góra. “For basic states and the so-called saddle points, we have determined such parameters as: nuclear masses, macroscopic energies, shell corrections and nuclear deformations – that is, the shapes of the nuclei in the ground state and in the saddle point. From them we deduced the energies of alpha decay between the ground states, the energies of the separation of one and two nucleons and the static, adiabatic heights of the fission barriers. ”

“Systematic calculations for odd nuclei, especially their cleavage barriers, are very rare – our work fills this gap” – adds Prof. Michał Kowal, Head of the NCBJ Theoretical Physics Department. “For systems with an odd number of protons, neutrons or both, we used the standard blocking BCS method. We could find the ground-state shapes and energies by minimizing seven axially symmetric strains. We searched for saddle points using the so-called “sinking” in three consecutive stages, using multidimensional deformation spaces, which involved the need to generate giant networks simulating various nuclear shapes. For this purpose, we used our supercomputer in the IT Center in Świerk for the calculations. ”

Some of the results obtained by the researchers concern parameters already known in the experiment and agree very well with these data. This confirms the correctness of the analysis carried out and allows us to believe that the determined values ​​of previously unknown parameters are reliable.

The researchers emphasize that they managed to create one of the most complete data sets available “on the market”, necessary for the analysis of cross sections, i.e. the production probabilities of super-heavy nuclei in individual synthesis channels. “The accuracy of reproducing the masses and other values ​​determined in the area analysed by us is one of the best existing estimates” – adds Prof. Janusz Skalski. “Our use of five- and seven-dimensional deformation spaces represents a significant improvement over other calculations performed so far. Our analysis is also one of the few that takes into account the odd nucleus, usually overlooked due to the difficulty of treating the odd nucleon.”

It is no coincidence that the results will go to the annals of Atomic Data and Nuclear Data Tables. Their importance is not limited to experiments aimed at creating new nuclides. “We have determined parameters, the knowledge of which may also be important for other areas of research” – explains Dr. Michał Kowal. “Among other things, we determined properties for the actinide nuclei, important from the point of view of reactor physics. Parameters determined and given in the paper can be used in astrophysical analyses and predictions concerning nucleosynthesis at particular stages of the universe’s evolution.”

P. Jachimowicz, M. Kowal, J. Skalski

Properties of heaviest nuclei with 98 ≤ Z ≤ 126 and 134 ≤ N ≤ 192,  

Atomic Data and Nuclear Data Tables
(Available online 19 December 2020, 101393, in press).

https://doi.org/10.1016/j.adt.2020.101393

Until February 7, 2020, the work is available online at https://authors.elsevier.com/a/1cGMz,26poewBO; later it will be available in print and for journal subscribers only.

New production methods of superheavy elements

Calculations made by Polish scientists in cooperation with a group of scholars from Dubna (Russia) allow predicting with previously unavailable accuracy the possibility of producing new isotopes of superheavy elements. In the article published in the prestigious journal Physics Letter B, they presented the most promising production channels for a wide range of isotopes with the atomic numbers from 112 to 118 in various configurations of nuclear collisions leading to their formation. The predictions appear to be reliable, as they are confirmed with excellent compatibility by the experimental data available for processes already tested.

In the article, to be released in October in the prestigious journal Physics Letters B, an international team of five scientists present new, promising predictions for the probabilities (cross-sections) of the production of heaviest isotopes of superheavy elements with the charge numbers from 112 to 118. Following future experiments, the calculations have been carried out for the fusion processes induced by Ca-48 calcium projectile.

Until now, the effects related to the shell nature of the saddle points in nuclear fission have not been considered at all, when calculating the probability of the formation of superheavy isotopes and  all researchers assume, that there are no quantum effects on this crucial nuclear configuration in the fission process. We included these effects in our research and provided a recipe for suppressing them as the formation temperature of a superheavy nuclear system increases. Such calculations have not been presented previously in the literature.

To get the result, the researchers used a statistical study, that generates millions of states above the ground state and the saddle point. They described in detail the method and results in a study submitted for another publication. Based on these results, it was quite easy to calculate the survival probability of the nuclei formed through a specific collision of a projectile with properly selected target. We simply estimated the competition for fission with different other decay channels, using a basic definition of the survival probability of a compound nucleus, without using an approximation. By studying the stability and analyzing the possible decay channels of the formed nuclei, scientists took into account decays by emission of neutrons, as well as protons and alpha particles.

The results presented in our  work correspond very well with the data obtained in recent experiments. At the same time, the authors point to the most promising production channels for new, so far unproduced isotopes, that could be used in future research. The excellent compatibility with existing excitation functions (probabilities of synthesis of superheavy nuclei) strengthens confidence in the correctness of the presented predictions. Channels emitting one proton or one alpha particle are particularly promising for some target-projectile combinations. This result is intriguing, because it may lead to new, unknown isotopes of superheavy nuclei. Since proposed reaction channels are not overly unusual, but rather are readily available by experiment, it will be soon revealed whether the predictions about the possibility of producing these new superheavy isotopes could be confirmed.

The original works are publicly accessible:

“Possibilities of direct production of superheavy nuclei with Z=112–118 in different evaporation channels”, J.Hong, G.G.Adamian, N.V.Antonenko, P.Jachimowicz, M.Kowal; Physics Letters B, Volume 809, 10 October 2020, 135760

https://www.sciencedirect.com/science/article/pii/S0370269320305633

“Level-density parameters in superheavy nuclei” A. Rahmatinejad, A. N. Bezbakh, T. M. Shneidman, G. Adamian, and N. V. Antonenko, P. Jachimowicz, M. Kowal

https://arxiv.org/pdf/2005.08685.pdf

Additional information:

The NCBJ Theoretical Physics Division deals with the study of the fundamental components of matter and the theoretical description of the basic interactions between them on both – micro and macro-world scales. The Division researches the basics of high and low energy nuclear physics (structure and dynamics), including the studies of the properties of heavy and superheavy nuclei. Our scientists are also developing the theory of the elementary particles, along with the supersymmetric models, that go beyond the currently known standard model, and quantum chromodynamics, that analyses the composition and interaction of nucleons. The Department is carrying out studies on the physics of non-linear phenomena, plasma physics, and the atomic condensates. Other areas of the research are theoretical cosmology and gravity theory, as well as string theory and its implications.

Photo: Cyclotron DC-280 in the Flerov Laboratory of Nuclear Reactions – Superheavy Element Factory in Joint Institute for Nuclear Research in Dubna. Credit: JINR