Nuclear Physics Division

The high energy part of the SPIRAL2 linear accelerator (new GANIL¹ accelerator scheduled for implementation in 2012) uses two types of superconducting cavities. IRFU's Accelerator, Cryogenics and Magnetism Department is responsible for the design and development of 12 cryomodules² of the first type, to be installed at the injector output. 

On December 8, 2008, the qualification prototype cryomodule was successfully tested at full power. The superconducting cavity attained an accelerating gradient of 10.3 MV/m (million volts per meter), far greater than the specified value of 6.5 MV/m.

 The shape of an atomic nucleus reflects the shell structure of the protons and neutrons of which it is formed. If the shells are completely filled, we speak of a "magic" nucleus, which is spherical in shape. Most nuclei, however, tend to be deformed because their shells are only partially filled. The most commonly encountered shapes are elongated (prolate) or flattened (oblate); these shapes can change from on nucleus to its neighbour by adding or removing a proton or neutron. In some cases it is sufficient to rearrange the protons or neutrons within the same nucleus to change its shape. The same nucleus can therefore assume different shapes corresponding to states of different energy. If such states come close in energy (one thousandth of the binding energy of the nucleus or so), the different shapes can mix. According to the laws of quantum mechanics, the nucleus can coexist in different shapes (e.g. elongated and flattened) at the same time. Such shape coexistence was observed in light krypton and selenium isotopes in a series of experiments performed by a team of researchers from the Nuclear Physics Department (SPhN) of IRFU .