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

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

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

Role of a resonance in the (β–p) decay of 11Be

Nuclear clustering is one of the most puzzling phenomena in subatomic physics. Numerous examples of such structures include the ground state of the 11Li nucleus with a halo of two neutrons or the famous Hoyle resonance at 12C, which plays a vital role in the synthesis of heavier elements in stars. The widespread presence of narrow resonances near the particle emission threshold suggests that this is a universal phenomenon in open quantum systems in which bound and unbound states strongly mix, resulting in the appearance of a collective state with the features of a nearby decay channel.  A new spectacular example of this phenomenon is the β delayed proton decay of the neutron halo ground state of 11Be. Studies within a shell model embedded in the continuum (SMEC) suggest the existence of a J𝜋 = 1/2+ collective resonance in 11B, carrying many characteristics of a nearby proton-decay channel, which explains this puzzling decay. The proximity of proton and tritium emission thresholds suggests that this resonance may also contain an admixture of the 3H cluster configuration To clarify the nature of this hypothetical 1/2+ resonance, study of 10Be(p,p)10Be reaction will be needed.

The narrow 5/2+ resonance in 11B at 11.600(20) MeV, which lies slightly above the neutron emission threshold and breaks down by the emission of the neutron or α particle, has a crucial effect   on the huge value of the 10B neutron capture cross-section. This suggests that the wave function of this resonance is strongly modified by the coupling to a nearby neutron emission channel. Indeed, in the SMEC calculations, there is a 5/26+ state near the neutron emission threshold, which strongly couples in L=2 partial wave to the channel [10B(3+)+n]5/2+. The theoretically determined maximal collectivization for this state is found ~110 keV above the neutron emission threshold and close to the experimental energy of the 5/2+ state. In the future, to clarify the impact of the virtual neutron state on the 10B(n,𝛾)11B reaction cross section, studies of the reaction 10Be(d,p)11B will be needed.

J.Okołowicz, M. Płoszajczak, W. Nazarewicz

Convenient location of a near-threshold proton-emitting resonance in 11Be

Physical Review Letters 124, 042502 (2020)

Precise studies of the three-nucleon force

Few-nucleon systems are studied at energies below the pion production threshold with the purpose of  precise testing the state-of-the-art nuclear interaction potentials. In the case of three-nucleon system, theoretical calculations predict significant effects of dynamics beyond the pairwise interaction between nucleons: a so-called three-nucleon force (3 Nucleon Force, 3NF). Experiments conducted with the use of large acceptance (nearly 4π) detection systems provide data for the deuteron breakup reaction in collision with a proton in various kinematic configurations of the final state. A reach set of data for differential cross sections is a basis for determining the effect of 3NF, testing approaches to include Coulomb repulsion between protons into theoretical calculations and tracing relativistic effects. Measurements of this reaction using the WASA@COSY detector were carried out in the upper range of deuteron beam energies of interest, 150-200 MeV/nucleon. The first set of results shows that even at such high energies cross-section for configurations in which protons fly “close together” (with a small relative momentum) is dominated by Coulomb repulsion between protons. In other kinematic regions, we observe the effects of 3NF, but there are also cases where all the theoretical predictions, regardless of the model, underestimate the experimental data. Relativistic calculations, so far not including 3NF in the potential, do not improve the description either. The data measured with BINA@KVI detector at the beam energy of 80 MeV/nucleon, indicate discrepancies of similar nature and in similar phase space regions, while previous measurements at the beam energy of 65 MeV/nucleon were very well described by calculations taking into account both the 3NF and the Coulomb repulsion. The source of this discrepancy remains a puzzle: are the current 3NF models imperfect or does the difference stem from neglecting relativistic effects? The progress of theoretical calculations and the continuation of research in the intermediate energy range using the BINA detector at CCB can help in solving the problem.

B.Kłos (M. Berłowski, I.Ciepał, E.Czerwiński, L.Jarczyk, B. Kamys,  St.Kistryn, W.Krzemień, P.Kulessa, A.Kupść, A.Magiera, P.Moskal, W.Parol, D.Pszczel, K.Pysz, M.Skurzok, J.Smyrski, J.Stepaniak, E.Stephan, A.Szczurek, A.Trzciński, A.Wrońska, J.Zabierowski, M.J.Zieliński, P.Żuprański, J.Golak, A.Kozela R.Skibiński, I.Skwira-Chalot, A.Wilczek, H.Witała),  WASA@COSY collaboration at al.

Three-nucleon dynamics in dp breakup collisions using the WASA detector at COSY-Jülich

Physical Review C 101, 044001 (2020)

W.Parol, A.Kozela( K.Bodek, J.Golak, St.Kistryn, B.Kłos, J.Kuboś, P. Kulessa, A. Łobejko, A.Magiera, R.Skibiński, I.Skwira-Chalot, E.Stephan, D.Rozpędzik, A.Wilczek, H.Witała, B.Włoch, A.Wrońska, J.Zejma) et al.

Measurement of differential cross sections for deuteron-proton breakup reaction at 160 MeV