PIPERADE

Important progresses have been achieved about the knowledge of the structure of the atomic nucleus with the study of the exotic nuclei produced in accelerator laboratories. Many phenomena have been evidenced showing the limits of the models developed with the help of studies of stable nuclei. In the domain of fundamental interactions, many experiments allowed to test the limits of the so called Standard Model (SM) and to show the need for new theoretical concepts. Be it for the study of the structure of the exotic nuclei or for the study of fundamental interactions, the future SPIRAL2 accelerator will allow to perform experiments with nuclei which are currently inaccessible and therefore a large effort is done by the nuclear physicists community to develop the equipment which will be used at SPIRAL2. A particular example is the DESIR facility to which the CENBG is contributing with a lot of efforts and in which many experimental devices will be installed for decay spectroscopy studies (BESTIOL), laser spectroscopy (LUMIERE) and mass measurements. For many experiments, very pure samples of exotic nuclei are needed to perform such studies. For example, the description of fundamental interactions is nowadays extremely precise and the determination of the fundamental parameters of the SM is obtained by very high precision experiments. Some of the parameters which are accessible by nuclear physics experiments are determined through the study of 0+->0+ beta decay transitions. Large improvements can be obtained by high precision measurements, in which the half lives, the branching ratios and the decay energy release will be determined for nuclei like 66As, 70Br… In the case of nuclear structure studies, the decay studies give access to spectroscopic information which is compared to models. For example, such measurements revealed that the N=20 magic number disappears for neutron rich isotopes. The structure of many nuclei which will be produced by SPIRAL2 is up to now totally unknown and a large experimental program will become possible. For the most exotic nuclei, it is predicted for example that new magic numbers corresponding to those of the harmonic oscillator could appear due to the disappearance of the spin orbit interaction. Another domain concerns the nuclear data needed in the framework of the electronuclear cycles. For new ones, for example based on 232Th, basic data like half lives, branching ratios, masses and neutron emission probabilities are missing and such data will become accessible by experimental measurements done at DESIR. In order to obtain large sample of pure or extra pure exotic nuclei, traditional methods using high resolution spectrometers are not suitable. We propose here to develop an original double trap system allowing to accumulate a large number of nuclei (>>10**4) with a mass resolution in the order of 10**-5. The principle consists in purifying radioactive nuclei in a first electromagnetic trap and to keep them in a second one in order to accumulate them in a large quantity. Before the trap, a RFQ cooler is used to slow down, focus and group the ions in bunches in order to inject them into the trap. The trap system itself is composed of a superconducting magnet and a system of electrodes to "keep" the ions in a circular movement which depends of their mass allowing therefore to separate the different isotopes and to produce mono-isotopic samples. To develop this original system, simulations will be done to determine the main characteristics of each element. Before being installed online at the SPIRAL2/DESIR facility, the project will be validated by means of a stable ion source system.