CLOver DETection system for Transfermium Elements – CLODETTE

We will upgrade the photon detection system at the focal plane of the recoil separator SHELS with a dedicated array of large volume (phase-I) Germanium detectors and a clover detector in close and compact geometry. All the Germanium detectors will be equipped with new specially designed Compton suppression shields to maximize the efficiency of the array as well as the signal to noise ratio.

We performed all the necessary Geant4 simulations for the project and established the specifications for all the elements. The clover detector CLODETTE was ordered and delivered in 2014.Its performance in terms of energy resolution is outstanding. The vacuum chamber has been built and is currently being assembled and vacuum tested in Russia. The new BGO shields should be delivered before the end of 2015.

The in-beam test of the new detection system at the focal plane of SHELS should take place in november 2015 or in the spring of 2016.

No scientific production yet (except some communications at conferences and collaboration meetings).

A recent article in the French scientific review “La Recherche” is dedicated to “ultraheavy atoms”. This shows once more that one of the major challenges of modern Nuclear Physics is to investigate the limits of nuclear existence. One simple and yet fundamental question is: what is the maximum number of protons a nucleus can sustain? To answer such a question, the synthesis of new elements with an ever increasing number of protons (Z=114 to 122) is carried out and motivated by the theoretical prediction of a new island of stability. Furthermore, superheavy nuclei provide a unique laboratory within which nuclear structure and dynamics under very intense Coulomb forces can be studied. While cross-sections to synthesize the heaviest elements are extremely low, the production rate of superheavy nuclei with proton numbers ranging from Z=100 to Z=106 is high enough to obtain significant information on their nuclear structure. Detailed internal-conversion-electron and gamma-ray spectroscopy of nuclei in this region of the nuclear chart is the prime motivation of the Franco-Russian GABRIELA (Gamma Alpha Beta Recoil Investigation with the Electromagnetic Analyzer VASSILISSA) project launched in 2003. The combination of high beam intensities and the availability of actinide targets makes GABRIELA@VASSILISSA a very unique experimental set-up, complementary to the S3 (Super Separator Spectrometer) project of heavy element spectroscopy with ultra-intense beams at SPIRAL2. The upgrade of the VASSILISSA separator, funded by the ANR within the SHELS (Separator for Heavy Element Spectroscopy, ANR-06-BLAN-0034) project, will allow the collaboration to access new and unexplored nuclei. The purpose of this new call is dedicated to transforming the photon-detection system at the focal plane of the VASSILISSA separator into a state-of-the-art array of Compton-suppressed Germanium detectors. This task will be done in collaboration with physicists from the Flerov Laboratory of Nuclear Reactions. In particular, recent experimental results have shown that the coincidence detection efficiency is crucial to disentangle the complex decay schemes of high-K isomers, whose existence is favored in this mass region. This is why we wish to upgrade the GABRIELA detector array with a dedicated array of coaxial Germanium detectors and a Clover detector in close and compact geometry, all equipped with new Compton suppression shields to maximize the efficiency of the array as well as the signal to noise ratio. Our Franco-Russian collaboration (between FLNR-JINR and IN2P3) started 7 years ago within the GABRIELA project. It has, therefore, stood the test of time and has proven to be very fruitful. Finally, the above-mentioned gamma detection system will be shared with the S3 project when it comes online in 2015-2016.