While the heaviest element on earth is 238-uranium (with traces of Pu and Np in natural nuclear reactors) whose lifetime is 5 billion years, the last 60 years have seen the synthesis of dozens of new elements in laboratory, with shorter lifetimes. In 2007, The heaviest elements which has been named is the Darmstadtium, with 111 protons. Z=112 has also been claimed, as well as Z=113 from a japanese team. From 2000, a Team working on the Dubna accelerator has claimed synthesis of elements Z=112, 114, 115, 116 and 118 by the process called "hot fusion". While a lot of works are undergone to validate these results, they still wait for a name on the Mendeleiev chart.
How many elements are still to be discovered with lifetime long enough to form an electronic cloud (t>10-14s) ? According to theoretical models, an island of stability is expected for Z=114 to 126, and N=184.
The search for Z=114 is a step toward this island.
The experimental works take place with the LISE3 device at GANIL.
Technical and scientific reponsabilities
- Co-spokesperson of the experiment
- Design and construction of the FULIS rotating wheel target chamber
- Command and control of the FULIS rotating wheel
- involvement in the realization and analysis of the experiment
The production cross sections of SHE synthesis are very low. They require the largest beam intensities on thin (<500µg/cm2) targets. This implies a strong heating of the target. To reduce this heating and prevent the target from destruction, we have used a rotating target that spread the energy deposit on a large surface.
The FULIS target has a radius of 36cm. It can rotate up to 2000 turms per minute. It is composed of several "sub-targets" with their own frame (16 lead targets in our experiment). The beam source is synchronized with the target rotation so that the beam does not touch the frames.
A surveillance system of the targets, developped by GANIL, enables to control their quality through the whole experiment. BaF2 scintillators near the target dected the gamma emission during the beam/tagret interaction. The gamma rate is correlated with the target position. A decrese of gamma emission is a hint for a deterioration or the full destruction of a targets. An excess shows that the beam is hitting a target frame.
2000 : reproduction of the 86Kr+208Pb → (Z=118) experiment performed at Berkeley. No event were found and the Berkeley results of Berkely were later disproved.
2001 : synthesis of Sg (Z=106) through the fusion of 54Cr on 208Pb. 10 events of 261Sg and 2 events of 260Sg were detected.
2002: Attempt of SHE synthesis by inverse kinematics (lead beam on chromium targets). The tests show that the LISE rejection power was not sufficient and must be improved for such reactions.
2004: Synthesis of 58Fe(208Pb,1n)265Hs(108). An excellent rejection factor was obtained: > 1011 . A total of 7 events were measured at 3 incident energies. The transmission was found to be 17%. Following this experiment, the LISE line was optimized to increase the transmission to 27%
2004: Attempts at the synthesis of Z=114 though the fusion of 76Ge on 208Pb. NO event were detected, which put the upper limit cross section to 1.2 pb.
2008: synthesis of 258-259Rf through the symmetric reaction 136Xe + 124Sn.
2013: Spectroscopy of 257Db produced in the 50Ti+209Bi fusion-evaporation reaction.
Last update : 11/22 2013 (2223)
Measurements of fission times and spectroscopy of Transfermium nuclei
The exact location of the stability regions of superheavy nuclei is not known, it varies and depends upon the nuclear structure models and on the interactions used to perform the calculations. The area around the element with Z=114 protons and N=184 neutrons has been predicted theoretically as a possible stability region. This has triggered the investigation for the formation of compound nuclei of charge Z~114.