V. M. Kokhanyuk

Production of actinium, thorium and radium isotopes from natural thorium irradiated with protons up to 141 MeV

Abstract Cross sections of 225Ac, 227Ac, 227Th and 228Th in thorium-232 targets irradiated with protons in the energy range 21–141 MeV have been measured. Based on these data, production yields of 225Ac and 223Ra in thick thorium targets have been calculated. It is possible to produce in proton energy range 60–140 MeV about 96 GBq (2.6 Ci) 225Ac per 10-d irradiation with 100 μA proton beam current and 10-d decay, and much higher amount of 223Ra. The impurities of 227Ac and 224Ra are important and need to be assessed for further medical applications.

Production of 225Ac and 223Ra by irradiation of Th with accelerated protons

The possibility of producing 225Ac and 223Ra by irradiation of natural 232Th with medium-energy protons was examined. Thorium foils were irradiated with 90-, 110-, and 135-MeV protons at the accelerator of the Institute for Nuclear Research, Russian Academy of Sciences, in Troitsk (Moscow oblast). The cumulative production cross sections for 225Ac were 6.7 ± 0.9, 9.8 ± 1.9, and 13.9 ± 1.5 mb, and for 227Th (223Ra precursor), 43 ± 5, 37 ± 6, and 35 ± 4 mb, respectively. Based on the experimental data and theoretical calculations, the possible yields of 225Ac and 223Ra in irradiation of thick thorium targets at various accelerators were determined. An efficient procedure was suggested for isolating the products from the irradiated targets: 225Ac, by liquid extraction and extraction chromatography, and 223Ra, by sublimation from a thorium-lanthanum melt followed by thermochromatographic separation in metallic titanium columns and extraction-chromatographic isolation of radium. The procedure allows production of large (units of curies) amounts of radiochemically pure 225Ac and 223Ra, which is promising for wide use of these radionuclides in nuclear medicine.

Isolation of Medicine-Applicable Actinium-225 from Thorium Targets Irradiated by Medium-Energy Protons

A method of isolation of actinium-225 for nuclear medical applications from thorium targets irradiated by protons is presented. It comprises liquid extraction and extraction chromatography separations. The method demonstrates high (> 85%) chemical yield and radionuclide purity of the final product. An impurity of 227Ac (0.1% at the end of bombardment) does not hinder 225Ac from being used for medical 225Ac/213Bi generators.

Sorption of radiostrontium from liquid rubidium metal

Sorption of radiostrontium (in particular, 82Sr) from liquid rubidium metal on various inorganic sorbents (metals and oxides) was studied. The temperature dependence and dynamics of the adsorption were studied, and the observed relationships were accounted for. The procedure developed allows efficient isolation of 82Sr from Rb targets after their irradiation with accelerated protons. Various versions of the procedure are considered, and prospects for the development of a new high-performance process for preparing 82Sr, in particular, using circulating Rb targets, were discussed.

Characterization of a 82Rb generator for positron emission tomography

Characteristics of the developed 82Rb medical generator intended for the production of Rubidium Chloride, 82Rb from Generator radiopharmaceutical for positron emission tomography (PET) are examined. The results of laboratory tests and clinical trials are presented. The influence of thermal sterilization on the ionexchange characteristics of the sorbent based on hydrous tin(IV) oxide is studied. The possibility of radiation “self-sterilization” of the generator column and of the maintenance of aseptic conditions in it throughout the generator operation life is assessed. In the course of operation of one generator, it is possible to obtain up to 19 L of a sterile and apyrogenic solution of the radiopharmaceutical with permissible content of radioactive and stable impurities. The efficiency of the 82Rb elution from the sorbent at different eluent flow rates is determined. The efficiency of using the generator in PET investigations in cardiology and oncology is demonstrated.