Improving the extraction of radioactive isotopes from MYRRHA linac targets by molecular sidebands

Brunier Philippe


Cottenier Stefaan, (KULeuven),

SCK•CEN Mentor

Aerts Alexander
+32 14 33 80 18

SCK•CEN Co-mentor

Popescu Lucia
+32 14 33 34 11

Expert group

Conditioning and Chemistry Programme

PhD started


Short project description

MYRRHA is an accelerator driven system currently under design at SCK•CEN. A fraction of the protons delivered by the linear accelerator of MYRRHA will not be used to drive the subcritical reactor but will be used for the irradiation of targets in dedicated stations to produce radioisotopes by the isotope separation on-line (ISOL) technique. Typically in ISOL, radioisotopes are extracted during target irradiation by simple evaporation.  However, when the vapor pressure of the radioisotope is close to or lower than that of the target material itself, this simple approach is not possible. Examples are the extraction of radioactive refractory elements from a tantalum target or the extraction of germanium isotopes from uranium-based targets.

In such cases, selective formation of volatile molecular compounds of the radioisotopes of interest is a promising solution to enable extraction. This may potentially strongly increase the range of accessible radioisotopes. Various approaches towards this so-called molecular sidebands formation exist. One of these is to expose the target to small quantities of a reactive gas during irradiation. This approach has already proven to be successful by using sulphur gas to selectively extract Sn from a UCx target.

Besides improving extraction yield, molecular sideband formation can be also used to suppression of undesired contaminants in the beam of isotopes, by shifting the mass of these contaminants in a completely separate range which can be easily filtered out by the mass separator.


Within this PhD project, key cases of interest will be identified and studied in detail for high-purity radioactive isotopes production through molecular sidebands formation. Specific attention will be paid to isotopes of refractory elements such as Os, which are not accessible with the current ISOL methods and to isotopes that show promise for pharmaceutical application.

Molecular sideband formation through interaction of reactive gases (oxygen, sulfur, halogens, …) with irradiated refractory targets (UCx, Ta, ...)  will be first studied by theoretical methods. The complex chemical equilibria that result from these interactions will be studied by the Gibbs energy minimization technique coupled with databases of known thermochemical properties of refractories and their compounds. Ab initio calculations will be used to estimate specific thermochemical properties, in case these are missing. These theoretical studies will allow identifying chemically feasible systems and will put limits on target operating conditions, which is required input for basic experiments and further optimization studies. The theoretical studies will be benchmarked against previous successes of the molecular sidebands technique, such as the very recent production of germanium beams using sulfur gas.

Systems that proved to be chemically feasible will be validated in experiments with stable isotopes using the high temperature evaporation equipment at SCK-CEN. Target materials that contain the element of interest will need to be prepared. A system that is able to dose reactive gases to a high temperature evaporation chamber will be constructed. With such a setup, the release of the element of interest from the target can be characterized, either by off line detection methods (such as ICP-MS) or by on-line mass spectrometry. Target composition, morphology or dispersion may need to be varied in order to optimize the release.

The most promising systems will be tested under proton-beam irradiation. Such experiments will be performed in the frame of the BeamLab collaboration, which includes accelerator facilities such as ALTO, CERN, GANIL and INFN.