RIB production at ISOL@MYRRHA: design-optimization analysis

Ashford Martin

Promoter

Aït Abderrahim Hamid, (UCL), hamid.abderrahim@term.ucl.ac.be

SCK•CEN Mentor

Popescu Lucia
lucia.popescu@sckcen.be
+32 14 33 34 11

Expert group

Proton Target Research

PhD started

2017-01-01

Short project description

The production of exotic Radioactive Ion Beams (RIB) is a challenging process. Because of the very short half-lives of these exotic nuclei, the RIB production using techniques such as chemical or mass separation off-line are discarded (the isotopes would completely decay before separation). The only way to produce these beams is using on-line methods: either in-flight separation (IFS), or the isotope separation on-line (ISOL). In the IFS method, a high-energy heavy-ion beam induces fragmentation reactions in a low-Z target material, the fragments emerging with beam-like velocities into a fragment separator where they are separated according to their mass over charge ratio. The resulting beam is characterized by high energy, but its purity is low (it always contains several isotopes of different neighboring species) and has a large energy spread and large transversal emittances. The ISOL method makes use of a light-particle beam (typically, protons, deuterons or alpha particles) impinging onto a high-Z target material, were spallation, fragmentation or fission reactions are induced. The reaction products are stopped into the bulk of the target material. By bringing the target material to high temperature, these isotopes diffuse and effuse efficiently towards an ion source, where they are (selectively) ionized and can be extracted in an ion beam through an extraction electrode. This beam is then purified by a high-resolution mass separator, where different atoms are separated according to their mass. The resulting beam is characterized by high purity and small transverse emittance, but, in the absencce of a post-accelerator, the energies of the ions are low (30-60 keV).

At SCK•CEN, plans are developed for the construction of a new-generation ISOL facility, offering high-intensity RIBs with stable operation over long periodes of time. This facility, named ISOL@MYRRHA, will make use of a small fraction of the proton beam which will become available at the envisaged MYRRHA accelerator driven system. Reliable RIB-intensity estimates are crucial to assess the scientific potential of a RIB facility such as ISOL@MYRRHA. These intensities can be optimized not only by increasing the power of the driver beam on target, but also through a careful production-module design optimization. Especially for the production of RIBs of very short-lived isotopes (in the millisecond range), minimizing the decay losses during the diffusion, effusion and beam-transport processes becomes important. Increasing the efficiency of a the ionization process is another important aspect, but falls outside the scope of the present PhD topic.

Objective

This PhD addresses the following objectives:

  • Monte Carlo simulations for estimating in-target production rates of several isotopes of interest by using different target materials and different target geometries with the ISOL@MYRRHA driver-beam parameters;
  • Estimation of diffusion and effusion efficiencies for the isotopes of interest;
  • Optimization of the target design in order to improve these efficiencies;
  • Monte Carlo simulations of the beam-power deposition in the target material and surroundings;
  • Thermal analysis of the target system, evaluation of cooling requirements;
  • Characterization of the proton beam after passage through the ISOL target;
  • In the scenario of a cascade of two targets one after the other, the second one making use of the proton beam which passes through the first target: (a) analyze the driver-beam characteristics after the first target and (b) propose, analyze and optimize RIB-production schemes with an overall improved efficiency for the simultaneous production of the two RIBs.