Sm using radiation-resistant ionic liquids

Several radioisotopes of elements of the lanthanide series, like Sm, are being applied in the field of therapeutic radiopharmaceuticals. These radiolanthanides are mainly being used for treatment of different types of bone cancer because of their favorable physical decay properties since they consist of β emitting radioisotopes. Moreover, they can also be used for bone imaging with the use of γ-ray detectors because of the emission of γ-photons during decay. The Sm radionuclide is produced via neutron irradiation of a target of enriched Sm, i.e. Sm(n,γ)Sm (t1/2 = 46.284 h). The stable Eu isotope is formed via subsequent β decay of Sm, which can be excreted by the human body without causing additional problems. The Sm radioisotope can be produced in the BR2 reactor, considered as a major facility for routine supply of radioisotopes, available at the Belgian Nuclear Research Institute (SCK•CEN). This production is characterized by high specific activities, i.e. 4500 Ci Sm per gram of Sm. Enriched samarium targets are irradiated during 4 days in a thermal neutron flux of 3.5 x 10 n/cm2s, being carried out in dedicated in-core devices within standard irradiation cycles of 3-4 weeks. BR2's current annual operating regime is based on five irradiation cycles. This high neutron flux is needed to ascertain the specific activity of the Sm radioisotope. Eu (t1/2 = 8.593 y) is also formed in the targets by neutron capture of Eu (decay product of Sm). By keeping the irradiation time rather short, the amounts of this impurity can be kept relatively low compared to the Sm activity, allowing the Sm to be used without purification from Eu. This is, however, associated with the drawback of a rather short shelf-life of the Sm product since the ratio of Sm/Eu decreases significantly with time. To increase the availability of the product, it would be beneficial if the shelf-life could be increased and/or the irradiation time could be prolonged. Therefore, the Eu has to be removed from the Sm. This, however, is not straightforward since trace amounts of europium have to be removed from large amounts of samarium. Since both are neighbouring lanthanides, the very similar chemical properties have to be taken into account. Moreover, one has to deal with the issues related to the handling of radioactive materials. To minimize the dose rate for the operators, a separation method that could be automatized would be beneficial. Furthermore, the radiation resistance of chemicals and materials that are used in the separation processes is important.