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

From cyclotrons to chromatography and beyond: a guide to the production and purification of theranostic radiometals

Recent clinical success with metal-based radiopharmaceuticals has sparked an interest in the potential of these drugs for personalized medicine. Although often overlooked, the success and global impact of nuclear medicine is contingent upon the purity and availability of medical isotopes, commonly referred to as radiometals. For nuclear medicine to reach its true potential and change patient lives, novel production and purification techniques that increase inventory of radiometals are desperately needed. This tutorial review serves as a resource for those both new and experienced in nuclear medicine by providing a detailed explanation of the foundations for the production and purification of radiometals, stemming from nuclear physics, analytical chemistry, and so many other fields, all in one document. The fundamental science behind targetry, particle accelerators, nuclear reactors, nuclear reactions, and radiochemical separation are presented in the context of the field. Finally, a summary of the latest breakthroughs and a critical discussion of the threats and future potential of the most utilized radiometals is also included. With greater understanding of the fundamentals, fellow scientists will be able to better interpret the literature, identify knowledge gaps or problems and ultimately invent new production and purification pathways to increase the global availability of medical isotopes.

Determination of the activity and nuclear decay data of 157Tb

Terbium-157 was radiochemically extracted from an irradiated tantalum target. Since the resulting material contained a significant impurity of 158Tb, 157Tb was isotopically purified using laser resonance ionization at the RISIKO mass separator in Mainz and then implanted on an aluminum (Al) foil. The implanted 157Tb was measured by two different calibrated gamma-ray spectrometers to determine photon emission rates. After dissolving the Al foil, a high purity 157Tb solution was obtained. The corresponding activity concentration was determined with a low relative uncertainty of 0.52% through a combination of liquid scintillation counting using the TDCR method and 4π(X,e)(LS)-(X,γ)(CeBr3) coincidence counting. By combining the results from all measurement techniques, emission intensities for K X-rays and gamma-rays were derived and found to be 16.05(31)% and 0.0064(2)%, respectively. The probability for K electron capture of the first forbidden non-unique transition to the ground state was determined to be 17.16(35)%. The probabilities for the electron-capture branch to the excited level and the ground state were found to be 0.084(4)% and 99.916(4)%, respectively. A Q+ value of 60.23(18) keV was estimated based on simplified BetaShape calculations, assuming an allowed transition.

The 146 Sm half-life re-measured: consolidating the chronometer for events in the early Solar System

The half-life of the extinct radiolanthanide146 Sm , important for both geochronological and astrophysical applications, was re-determined by a combination of mass spectrometry and α -decay counting. Earlier studies provided only limited information on all potential factors that could influence the quantification of the half-life of146 Sm . Thus, special attention was given  here to a complete documentation of all experimental steps to provide information about any possible artifacts in the data analysis. The half-life of146 Sm was derived to be 92.0 Ma ± 2.6 Ma, with an uncertainty coverage factor of k = 1 .

Investigating the hard X-ray production via proton spallation on different materials to detect elements

Various atomic and nuclear methods use hard (high-energy) X-rays to detect elements. The current study aims to investigate the hard X-ray production rate via high-energy proton beam irradiation of various materials. For which, appropriate conditions for producing X-rays were established. The MCNPX code, based on the Monte Carlo method, was used for simulation. Protons with energies up to 1650 MeV were irradiated on various materials such as carbon, lithium, lead, nickel, salt, and soil, where the resulting X-ray spectra were extracted. The production of X-rays in lead was observed to increase 16 times, with the gain reaching 0.18 as the proton energy increases from 100 MeV to 1650 MeV. Comparatively, salt is a good candidate among the lightweight elements to produce X-rays at a low proton energy of 30 MeV with a production gain of 0.03. Therefore, it is suggested to irradiate the NaCl target with 30 MeV proton to produce X-rays in the 0-2 MeV range.

Determination of the half-life of gadolinium-148

The half-life of the alpha-emitter ¹⁴⁸Gd was measured using the "direct method", in which the number of atoms is directly determined and their activity is then measured. Pure Gd samples containing megabecquerels of ¹⁴⁸Gd were obtained by reprocessing proton-irradiated tantalum material. Multicollector-inductively coupled plasma mass spectrometry was performed to determine the amount of ¹⁴⁸Gd atoms retrieved. The activity of the ¹⁴⁸Gd atoms contained in the Gd sample was measured by means of alpha-spectrometry. The half-life of ¹⁴⁸Gd was deduced to be 86.9 years, with a combined uncertainty of 4.5%.

High precision half-life measurement of the extinct radio-lanthanide Dysprosium-154

Sixty years after the discovery of ¹⁵⁴Dy, the half-life of this pure alpha-emitter was re-measured. ¹⁵⁴Dy was radiochemically separated from proton-irradiated tantalum samples. Sector field- and multicollector-inductively coupled plasma mass spectrometry were used to determine the amount of ¹⁵⁴Dy retrieved. The disintegration rate of the radio-lanthanide was measured by means of α-spectrometry. The half-life value was determined as (1.40 ± 0.08)∙10⁶ y, with an uncertainty reduced by a factor of ~ 10 compared to the currently adopted value of (3.0 ± 1.5)∙10⁶ y. This precise half-life value is useful for the the correct testing and evaluation of p-process nucleosynthetic models using ¹⁵⁴Dy as a seed nucleus or as a reaction product, as well as for the safe disposal of irradiated target material from accelerator driven facilities. As a first application of the half-life value determined in this work, the excitation functions for the production of ¹⁵⁴Dy in proton-irradiated Ta, Pb, and W targets were re-evaluated, which are now in agreement with theoretical calculations.

How accurate are half-life data of long-lived radionuclides?

We have consulted existing half-life data available in Nuclear Data Sheets for radionuclides with Z < 89 in the range between 30 and 108 years with emphasis on their uncertainty. Based on this dataset, we have highlighted the lack of reliable data by giving examples for nuclides relevant for astrophysical, environmental and nuclear research. It is shown that half-lives for a substantial number of nuclides require a re-determination since existing data are either based on one single measurement, are contradictory or are associated with uncertainties above 5%.

Radiochemical Determination of Long-Lived Radionuclides in Proton-Irradiated Heavy Metal Targets: Part II Tungsten

In this study, proton-irradiated tungsten targets, up to 2.6 GeV, were investigated for the purpose of the experimental cross-section measurements. Radiochemical separation methods were applied to isolate the residual long-lived alpha-emitters ¹⁴⁸Gd, ¹⁵⁴Dy, and ¹⁴⁶Sm and the beta-emitters ¹²⁹I and ³⁶Cl from proton-irradiated tungsten targets. The molecular plating technique has been applied to prepare ¹⁴⁸Gd, ¹⁵⁴Dy, and ¹⁴⁶Sm samples for alpha-spectrometry. Production cross-sections of ¹²⁹I and ³⁶Cl were determined by means of accelerator mass spectrometry. The results are compared with theoretical predictions, obtained with the INCL++-ABLA07 codes, showing good agreement for ³⁶Cl and ¹⁴⁸Gd, while a factor of 4 difference was observed for ¹⁵⁴Dy, similar to the results obtained for tantalum targets.

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.