A working group of physicists coming from GANIL (France), Soreq Nuclear Research Center and Weizmann Institute (Israel), Rez (Czech republic) has been formed in order to study the production options of intense light radioactive ions beams at the future SPIRAL2 facility in the framework of the European project SPIRAL2 Preparatory Phase. All nuclei between helium and silicon were studied in details, among them 6He, 14O, 15O, 8Li were selected as priorities because of their scientific interest and also because of their technical challenges.
Figure: Thermal simulation of the carbon-target used to produce 14O at Spiral 2 (A. Pichard)
The production of 6He at GANIL for instance,, at the present time SPIRAL1 can deliver 3x107 1+ and 5x106 2+ post-accelerated ions/s. Extensive simulations of converters and targets have been carried out at Soreq and tested using a commercial 14 MeV neutron generator. Meanwhile, the GANIL group measured in Finland (Jyvaskyla) neutron yields of carbon, light and heavy water bombarded with 40 MeV deuterons that are used to calculate yields of neutron-induced reactions. The in-target 6He yields are estimated above 1013 /s at SARAF and above 5x1011 /s (1mAp) at SPIRAL2. With reasonable release, ionization and charge breeding efficiencies, one may hope for an improvement close to 100 times with respect to SPIRAL1 intensities. Both institutes have chosen 9Be(n,a) for production of 6He. The same 40 MeV deuteron beam generates neutrons but converters are lithium for SARAF at Soreq, and (at least at the start) carbon for SPIRAL2. Beryllium oxide BeO has been selected as target material. Thermal tests were performed by the Weizmann group and also at ISOLDE. A test of production was performed at CERN-ISOLDE in April 2009, the results are very positive since the 6He ions were strongly produced and well released by the target. The next steps will be to define safety issues and waste management, and to build the oven with the target holder.
Likewise, 14O ions can be produced at SPIRAL2 through the 12C(3He,n)14O reaction. Using realistic conditions, one could achieve an accelerated 14O beam intensity above 107 pps (SPIRAL1 delivers about 5x105 pps after acceleration). Last year, tests were performed at Bordeaux to measure the thermal properties of thin flexible carbon foils needed for this production. In parallel, thermal simulations are carried out at GANIL to define the best geometry of the target which should sustain the 5 kW of the primary beam. The cross section of the reaction will be measured accurately this year in Czech Republic (Rez) to better determine the expected production. Moreover, a proposal was accepted at Orsay to measure the release properties of this kind of targets. This measurement will be performed in 2010.