The heaviest elements known were produced by using the emblematic calcium-48 beam associated to the actinide targets up to californium, the ultimate element available at tens of milligrams amounts. No elements were discovered yet above oganesson (Z=118) despite trial of several beam-targets combinations. With its two more protons with respect to calcium, the titanium-50 is expected to be the best option to open the road to the synthesis of the 120^th element of the periodic table.

An intense titanium-50 beam was developed at RIKEN Nishina Center in collaboration with IPHC Strasbourg. As a first step, it was used to determine the optimal bombarding energy for the production of oganesson-294 by means of barrier distributions measurements. This step was crucial regarding the fact that the traditional excitation function study getting extremely time consuming and getting almost impossible in the case of the heaviest element quest.

This 2 x 10¹² particles per second beam was used to try to produce oganesson-294 by bombarding a curium-248 target in 2017. The experiment was conducted down to the point where the production probability achieved was almost twice lower (0,27 pb) than the one corresponding to the synthesis performed with calcium (0,5 pb). The experiment entered in the probability window foreseen for the production of oganesson with titanium-50 beam. At that point, the experiment was paused in order to enable the start of the experiment aiming at the production of new element with Z=119 and to benefit later from more intense titanium-50 beams.

Following theoretical predictions, replacement of calcium-48 by titanium-50 would lead to one order of magnitude reduction in production cross-section, and a further replacement by chromium-54 would lead to an additional loss of a factor 10 in production probability. A recent experiment conducted in Berkeley associating an intense titanium-50 beam with plutonium-244 target demonstrated experimentally this drastic reduction. It was confirmed short after by another experiment done in recently in Dubna where these two beams were associated with plutonium-242 and uranium-238 targets respectively.

Combining all these experiments, one expects now to be able to produce oganesson at a few tens of fb level. With present-day titanium-50 beam intensities in several major labs, this could now be achieved within a few weeks of beam time. This experiment will be a major confirmation step before going to the synthesis of element 120, both for experimentalists aiming at new element properties studies and for theoreticians studying reaction mechanisms.

In addition to the possibilities offered by these unprecedented beam intensities in terms of new elements study, the availability of more intense beams enables also the study of chemical properties of the heaviest elements known in a region where the periodic table starts to host as last member of a row, elements that are not anymore Chemical analogues of proceeding elements in the same column due to the fingerprint of relativity.

Further information can be found in the press release of this article.

(Written by B. J.P. Gall on behalf of all authors)

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