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Development for ALTO

Radioactive beams

It might be worth reminding ourselves just how big a historical role the IPN has played in the development of the ISOL technique in France. The IPN was a precursor of this technique with the ISOCELE system at the Orsay synchrocyclotron (SC) and has always maintained the very highest level of know-how through its long-standing close links with ISOLDE. It made a major contribution to the introduction of this technique at GANIL, leading to the advent of SPIRAL. The IPN’s contribution to the SPIRAL2 project in the field of target-source assemblies has also been essential. A laboratory where such techniques are maintained and developed is clearly iconic in its directly associated physics fields, i.e., “low energy” physics, in other words, that which requires exotic beams at source extraction energies with excellent optical quality (laser spectroscopy), or physics “at rest” (study of radioactive decays). As mentioned earlier, IPN physicists intend to play a central role in this field by putting the potential of ALTO to its fullest use, by constructing a sizeable community around this installation, and by being a driving force in the DESIR project with SPIRAL2. This ambition cannot be realized unless the ALTO installation is provided with European class instrumentation : BEDO, SPECOLOR, POLAREX (the last project being led by the CSNSM). The IPN’s originality in the ISOL field is that when it develops new beams (new target source assemblies, etc.), this is always in close collaboration with physics programmes being developed, as recently illustrated by the joint success of the PARRNe/photofission project in collaboration with the study of the N=50 shell effect around 78Ni.

New avenues are still available to be explored with the ALTO installation. Examples of these include

• Shortening the target to take advantage of the natural distribution of photofission products in order to optimize exit time

• Chemical tests in the target to optimize the production of Lanthanides

• Negative ionization tubes to eliminate contaminants from surface ionization, or trap based methods like LIST

• Thorium fission instead of Uranium fission

• the search for new matrices : new carburation techniques, the use of nanotubes etc., or the photo-production of 8Li beams, which is of great interest in nuclear astrophysics and the physics of materials.

To summarize, the strategy we propose is to maintain (or regain) our leadership in the field of nuclear structures in the 78Ni and 132Sn regions :

in the first phase : by using ALTO to its full potential (10µA electrons) through optimizing the three parameters we have available : (i) purity of beams (ii) selectivity of detection systems (iii) availability of the beam in order to allow room for long and/or exploratory experiments.

in the second phase : by getting involved in the DESIR project within the Phase 2 of SPIRAL2. Depending on how this phase 2 of the project evolves, however, it seems wise to start anticipating (at least up to the feasibility study stage) an increase of 2 or 3 orders of magnitude in the intensity of beams from fission products, thus engineering an opening toward a second ALTO phase. To that end, when replacing certain components (certain of which were already old when the project started, like the klystron and the modulator), it would be useful to procure replacements that can attain in the order of 1mA electrons.

Stable Beams

Mechanisms above the Coulomb barrier, or more generally, at energies in the order of 10AMeV, have been used very little so far in the mass production of radioactive beams, whether this be through the ISOL technique (where the chief mechanisms remain spallation, fission, and fragmentation) or through the so-called in-flight technique (almost exclusively fragmentation). Interest has recently been rekindled in multinucleon exchange mechanisms during collisions that range from near-elastic to deeply inelastic ; this is mainly to their successful use at Legnaro National Laboratories, but some thinking has also taken place on the physical opportunities opened up by the post-acceleration of intermediate mass nuclei with CIME, relatively limited in energy. Alongside this, the European collaboration ECOS has clearly identified the need for the community to have access to a machine generating stable beams of very high intensity (in the order of 1mA) at energies close to the barrier (10-20 AMeV) to serve a vast field of physics research.

The IPN, birthplace of the discovery of deeply inelastic mechanisms, can and must open the way for their use in the production of radioactive beams. The IPN has a considerable advantage when it comes to supporting the necessary R&D, namely its Tandem facility, which supplies a wide variety of stable beams at adequate energies and enables very long or highly exploratory experiments. Some exploratory experiments, especially at very low angles, can already be conducted with the BACCHUS spectrometer, which has a very suitable design for eliminating the charge states of the primary beam. What’s missing from Tandem is the intensity ; therefore physics study programmes using very high intensity (>500 µA) stable beams of 15-20AMeV must be completed on other existing installations like those at Jyväskylä, Legnaro, or LINAG. Typical such programmes include the study of N=Z nuclei close to the neutron drip line, the study of high rank nuclear symmetries, etc. (physics fields singled out by the ECOS collaboration). An interesting alternative for covering the essential elements of “ECOS” type physics could be an accelerator designed to use ANDROMEDE as a “driver”, injecting beams of the required intensity into a linear supraconductor post-accelerator, for which IPN has the technology. This project, which we might name “ANDROMEDE 2” for convenience, could occupy the “ECOS type” physics slot and help release pressure on the existing accelerators ; secondarily, it could leave LINAG the role of deuton driver for the mass production of neutron-rich nuclei by fission in phase 2 of SPIRAL2.



Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE)
UMR 8608 - CNRS/IN2P3

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