Synthesis of Superheavy Nuclei: Nearest and Distant Opportunities

Abstract

There are only 3 methods for the production of heavy and superheavy (SH) nuclei, namely, a sequence of neutron capture and beta(−) decay, fusion reactions, and multinucleon transfer reactions. A macroscopic amount of the long-living SH nuclei located at the island of stability may be produced by using the pulsed nuclear reactors of the next generation only if the neutron fluence per pulse will be increased by about three orders of magnitude. Low values of the fusion cross sections and very short half-lives of nuclei with Z > 120 also put obstacles in synthesis of new elements. At the same time, an important area of SH isotopes located between those produced in the cold and hot fusion reactions remains unstudied yet. This gap could be filled in fusion reactions of 48 Ca with available lighter isotopes of Pu, Am, and Cm. New neutron-enriched isotopes of SH elements may be produced with the use of a 48 Ca beam if a 250 Cm target would be prepared. In this case, we get a real chance to reach the island of stability owing to a possible beta(+) decay of 291 114 and 287 112 nuclei formed in this reaction with a cross section of about 0.8 pb. Multinucleon transfer processes look quite promising for the production and study of neutron-rich heavy nuclei located in the upper part of the nuclear map not reachable by other reaction mechanisms. Reactions with actinide beams and targets are of special interest for synthesis of new neutron-enriched transfermium nuclei and not-yet-known nuclei with closed neutron shell N = 126 having the largest impact on the astrophysical r-process. The estimated cross sections for the production of these nuclei allows one to plan such experiments at currently available accelerators.

Super-heavy element research

“…One should also note that increasing the atomic number brings us closer to the closed proton shell at Z = 120-126 predicted by some microscopic models, which could also increase shell effects. However, most calculations predict much lower cross sections for complete-fusion reactions with projectiles heavier than 48 Ca [59,61,62,[79][80][81][82][83].…”

“…For calculation of the probability P fus , different models are used which suppose different mechanisms of CN formation. In the multidimensional Langevintype dynamical approach [56][57][58][59]79], it is assumed that two touching nuclei lose their 'individualities' at the touching point and one strongly deformed heavy nucleus with summary mass evaluates in the multidimensional space of deformations into a spherical CN or goes into fission channels. A somewhat different scenario of this process is assumed in the 'dinuclear system model' [81,82].…”

Influence of hexadecapole deformation on production cross sections of superheavy nuclei

“…Their work adopted the the fission barrier heights [53] based on the Warsaw macroscopic-microscopic model [54]. Almost an equally small cross section for the 54 Cr+ 248 Cm reaction was predicted by Zagrebaev et al [64]; they obtained 15 and 28fb, respectively. Liu et al [11], using the modified fusion by diffusion model, obtained 12 and 34 fb, respectively.…”

Super Heavy Elements

“…For the synthesis of new elements with atomic number Z > 118 heavier beams than 48 Ca have to be used, for example 50 Ti or 54 Cr. This is expected to result in a significant reduction of the cross section to a level of 0.01-0.1 picobarn for the synthesis of Z = 119, 120 according to PoS(Bormio2015)038 recent theoretical predictions [31]. In all experimental attempts for the synthesis of elements with Z = 119,120 made so far no event was observed leading to cross section limits as low as about 0.1 picobarn [32].…”