Production of Mass-Separated Erbium-169 Towards the First Preclinical in vitro Investigations

The β--particle-emitting erbium-169 is a potential radionuclide toward therapy of metastasized cancer diseases. It can be produced in nuclear research reactors, irradiating isotopically-enriched 168Er2O3. This path, however, is not suitable for receptor-targeted radionuclide therapy, where high specific molar activities are required. In this study, an electromagnetic isotope separation technique was applied after neutron irradiation to boost the specific activity by separating 169Er from 168Er targets. The separation efficiency increased up to 0.5% using resonant laser ionization. A subsequent chemical purification process was developed as well as activity standardization of the radionuclidically pure 169Er. The quality of the 169Er product permitted radiolabeling and pre-clinical studies. A preliminary in vitro experiment was accomplished, using a 169Er-PSMA-617, to show the potential of 169Er to reduce tumor cell viability.

243Am certified reference material for mass spectrometry

The Joint Research Centre, in cooperation with the Commissariat à l’Energie Atomique et aux Energies Alternatives, produced a novel 243Am spike reference material for mass spectrometry. Americium solution with an isotopic composition of 88% 243Am and 12% 241Am was used as the source for the preparation of the spike material. The certified value of 5.696 (11) nmol g−1 for the amount content of 243Am and 0.136138 (54) for the n(241Am)/n(243Am) amount ratio were assigned. The assigned values from mass spectrometry were confirmed by alpha-particle spectrometry, alpha-particle counting at a defined solid angle, and high-resolution gamma-ray spectrometry. Furthermore, an external validation of the certified values was obtained from the results of an interlaboratory comparison exercise, using this americium reference solution as the test sample.

Selective Cs-removal from highly acidic spent nuclear fuel solutions

Thirty liters of highly acidic spent nuclear fuel solutions need to be disposed at the “Hot Laboratory (hotlab)” facility in Paul Scherrer Institut (PSI), Switzerland. In order to significantly reduce the γ dose rate before proper disposal treatment, 137Cs must be removed. In the here presented sub-project, the ion-exchange method was evaluated. Two promising sorbents, CLEVASOL® and AMP (ammonium molybdophosphate), and two derived products AMP_PAN (AMP immobilized in polyacrylonitrile) and AMP/SiO2 (AMP immobilized on silica gel) were tested by the batch method using model solutions of important high-yield fission products (Cs, Eu, Zr, Ru, Pd and Ag), as well as U and Pu. The results showed that AMP, AMP/SiO2 and AMP_PAN have higher selectivity for Cs than CLEVASOL® in 0.1–8 M (mol/L) HNO3 solutions. 4 M HNO3 solution was identified as the most suitable condition for Cs-removal with AMP, AMP_PAN and AMP/SiO2 due to the still sufficiently high separation factor of Cs from other metal ions and an acceptable volume increase factor after dilution. The follow-up kinetic studies on AMP, AMP_PAN and AMP/SiO2 indicated that although Cs exchange on AMP and AMP/SiO2 is faster than on AMP_PAN in the first 5 min, they all nearly reach equilibrium after 30 min of contacting time. The isotherm curves of Cs adsorption on AMP, AMP_PAN and AMP/SiO2 in 4 M HNO3 showed that the maximum sorption capacity of Cs is reached asymptotically. The results from Langmuir isotherm modeling agree with results from other publications.

Separation and recovery of exotic radiolanthanides from irradiated tantalum targets for half-life measurements

The current knowledge of the half-lives (T_1/2) of several radiolanthanides is either affected by a high uncertainty or is still awaiting confirmation. The scientific information deriving from this imprecise T_1/2 data has a significant impact on a variety of research fields, e.g., astrophysics, fundamental nuclear sciences, and nuclear energy and safety. The main reason for these shortcomings in the nuclear databases is the limited availability of suitable sample material together with the difficulties in performing accurate activity measurements with low uncertainties. In reaction to the urgent need to improve the current nuclear databases, the long-term project “ERAWAST” (Exotic Radionuclides from Accelerator Waste for Science and Technology) was launched at Paul Scherrer Institute (PSI). In this context, we present a wet radiochemical separation procedure for the extraction and purification of dysprosium (Dy), terbium (Tb), gadolinium (Gd), and samarium (Sm) fractions from highly radioactive tantalum specimens, in order to obtain ¹⁵⁴Dy, ^157-158Tb, ^148,150Gd, and ¹⁴⁶Sm samples, needed for T_1/2 determination studies. Ion-exchange chromatography was successfully applied for the separation of individual lanthanides. All separations were conducted in aqueous phase. The separation process was monitored via γ-spectrometry using suitable radioactive tracers. Both the purity and the quantification of the desired radiolanthanides were assessed by inductively coupled plasma mass spectrometry. Test experiments revealed that, prior to the Dy, Tb, Gd, and Sm separation, the removal of hafnium, lutetium, and barium from the irradiated tantalum material was necessary to minimize the overall dose rate exposure (in the mSv/h range), as well to obtain pure lanthanide fractions. With the herein proposed separation method, exotic ¹⁵⁴Dy, ^157-158Tb, ^148,150Gd, and ¹⁴⁶Sm radionuclides were obtained in sufficient amounts and purity for the preparation of samples for envisaged half-life measurements. During the separation process, fractions containing holmium, europium, and promethium radionuclides were collected and stored for further use.