Wayne A. Taylor

Application of ion exchange and extraction chromatography to the separation of actinium from proton-irradiated thorium metal for analytical purposes

Actinium-225 (t1/2=9.92d) is an α-emitting radionuclide with nuclear properties well-suited for use in targeted alpha therapy (TAT), a powerful treatment method for malignant tumors. Actinium-225 can also be utilized as a generator for (213)Bi (t1/2 45.6 min), which is another valuable candidate for TAT. Actinium-225 can be produced via proton irradiation of thorium metal; however, long-lived (227)Ac (t1/2=21.8a, 99% β(-), 1% α) is co-produced during this process and will impact the quality of the final product. Thus, accurate assays are needed to determine the (225)Ac/(227)Ac ratio, which is dependent on beam energy, irradiation time and target design. Accurate actinium assays, in turn, require efficient separation of actinium isotopes from both the Th matrix and highly radioactive activation by-products, especially radiolanthanides formed from proton-induced fission. In this study, we introduce a novel, selective chromatographic technique for the recovery and purification of actinium isotopes from irradiated Th matrices. A two-step sequence of cation exchange and extraction chromatography was implemented. Radiolanthanides were quantitatively removed from Ac, and no non-Ac radionuclidic impurities were detected in the final Ac fraction. An (225)Ac spike added prior to separation was recovered at ≥ 98%, and Ac decontamination from Th was found to be ≥ 10(6). The purified actinium fraction allowed for highly accurate (227)Ac determination at analytical scales, i.e., at (227)Ac activities of 1-100 kBq (27 nCi to 2.7 μCi).

Production of strontium-82 for the Cardiogen® PET generator: a project of the Department of Energy Virtual Isotope Center

In December of 1989, the United States Food and Drug Administration approved 82Rb chloride in saline solution for cardiological perfusion imaging by positron emission tomography (PET). The solution is derived from a 82Sr generator system that is presently manufactured by Bristol Myers Squibb and distributed for clinical application in the United States by Bracco Diagnostics, Inc. Many years of research and development by people in several institutions led up to the approval for clinical use. Currently, there are about 15 sites in the U.S. that perform clinical myocardial perfusion imaging by PET using 82Rb chloride from the generator. In order to manufacture the generators, Bristol Myers Squibb requires about 1600 mCi of 82Sr every 30 days. The United States Department of Energy and MDS Nordion, Canada are the current suppliers with qualified Drug Master Files for the production and distribution of this nuclide for the Cardiogen® generator. These two entities have worked together over the years to assure the regular, reliable supply of the 82Sr. Here we describe the facilities and methods used by the Department of Energy in its Virtual Isotope Center to make and distribute the nuclide.

Activation rates and chemical recovery of67Cu produced with low energy proton irradiation of enriched70Zn targets

Copper-67 is a radioisotope with significant potential for diagnostic and therapeutic applications in nuclear medicine. Despite its promise,67Cu has failed to make an impact in clinical nuclear medicine, primarily because it is available sporadically, and in limited quantities. Common methods of production rely on high energy proton irradiation of natural zinc targets or on induced reactions using high energy neutrons at nuclear reactors. We have evaluated alternative production methods that could provide year-round adequate supply of this isotope. Using a low energy accelerator, we have studied the production of67Cu by proton reactions on enriched70Zn. Our results indicate that it is possible to produce useful quantities of67Cu from the irradiation of enriched70Zn with protons that have energies of less than 20 MeV. Production rates are higher than currently used methods at high energy accelerators or reactors. This isotope can be made available throughout the year as a result of this research.

Proton beam simulation with MCNPX/CINDER'90: Germanium metal activation estimates below 30 MeV relevant to the bulk production of arsenic radioisotopes

Germanium metal targets encapsulated in Nb shells were irradiated in a proton beam. Proton and secondary neutron beam fluences as well as radionuclide activity formation were modeled using MCNPX in combination with CINDER90. Targets were chemically processed using distillation and anion exchange. Good agreement between the measured radiochemical yields and MCNPX/CINDER90 estimates was observed. A target of pentavalent (73,74)As radioarsenic for neutron activation studies was prepared.

Radiochemical study of re/w adsorption behavior on a strongly basic anion exchange resin

Abstract Rhenium-186g is a radionuclide with a high potential for therapeutic applications. It emits therapeutic β− particles accompanied by low energy γ-rays, which allows for in-vivo tracking of the radiolabeled compound and dosimetry estimates. The current reactor production pathway 185Re(n, γ)186gRe produces low specific activity 186gRe, thereby limiting its therapeutic application. Work is underway to develop an accelerator-based, charged particle induced production method for high specific activity 186gRe from targets of enriched 186W. To optimize the chemical 186gRe recovery method, batch studies have been performed to characterize the adsorption behavior of Re and W on a strongly basic anion exchange resin. An in-depth physicochemical profile was developed for the interaction of Re with resin material, which showed the reaction to be endothermic and spontaneous. Basic (NaOH) and acidic (HNO3) matrices were used to determine the equilibrium distribution coefficients for Re and W. The resin exhibits the best affinity for Re at slightly basic conditions and little affinity above moderately acidic concentrations. Tungsten has low affinity for the resin above moderately basic concentrations. A study was performed to examine the effect of W concentration on Re adsorption, which showed that even a high ionic WO42– strength of up to 1.9 mol kg–1 does not significantly compromise ReO4– retention on the resin.

Transfer of copper from metallothionein to nonmetallothionein proteins in cultured cells

Copper uptake and distribution with time among cytoplasmic proteins were followed in cultured cells under several conditions: (1) CHO cells, which cannot synthesize metallothioneins, were labeled with67Cu in the presence of 100 μM ZnCl2; (2) Cdr30F9 cells, which contain some constitutive metallothionein (MT), were labeled in the absence of additional ZnCl2 and; (3) Cdr30F9 cells were labeled in the presence of ZnCl2, under which conditions they synthesized additional metallothioneins. The exogenous67Cu and ZnCl2, where present, were then removed, and the distributions of67Cu among size fractions of the cellular proteins were observed at intervals for 16 h. In addition, a culture identical to condition (3) above was also treated with 100 μM ZnCl2 during the redistribution period. The67Cu was initially resolved into three peaks by Sephadex G-75 chromatography: high molecular weight, intermediate molecular weight, and MT. The67Cu in the MT fraction decreased with at1/2 of 10–12 h. In contrast to this, generally, in cells with a higher initial67Cu bound to metallothionein, there was a progressive increase in the amount of67Cu eluting with the high- and intermediate-molecular-weight fractions. Since no other source of67Cu was available, these experiments suggest that copper stored in MT can be transferred to other proteins in these cells.

Isolation of 163Ho from dysprosium target material by HPLC for neutrino mass measurements

Abstract The rare earth isotope 163Ho is of interest for neutrino mass measurements. This report describes the isolation of 163Ho from a proton-irradiated dysprosium target and its purification. A Dy metal target was irradiated with 16 MeV protons for 10 h. After target dissolution, 163Ho was separated from the bulk Dy via cation-exchange high performance liquid chromatography using 70 mmol dm–3 α-hydroxyisobutyric acid as the mobile phase. Subsequent purification of the collected Ho fraction was performed to remove the α-hydroxyisobutyrate chelating agent and to concentrate the Ho in a low ionic strength aqueous matrix. The final solution was characterized by MC-ICP-MS to determine the 163Ho/165Ho ratio, 163Ho and the residual Dy content. The HPLC purification process resulted in a decontamination factor 1.4E5 for Dy. The isolated Ho fraction contained 24.8 ± 1.3 ng of 163Ho corresponding to holmium recovery of 72 ± 3%.

Recovery of hafnium radioisotopes from a proton irradiated tantalum target

The178m2Hf nucleus, with its long half-life (31 y) and high-spin isomeric state (16+) is desired for new and exotic nuclear physics studies. The Los Alamos Radioisotope Program irradiated a kilogram of natural tantalum at the Los Alamos Meson Physics Facility in early 1981. After fifteen years of decay, this target was ideal for the recovery of178m2Hf. There was more than a millicurie of178m2Hf produced during this irradiation and there has been a sufficient period of time for most of the other hafnium radioisotopes to decayed away. Traditionally, separation techniques for recovering hafnium isotopes from tantalum targets employ solvent extractions with reagents that are considered hazardous. These techniques are no longer condoned because they generate a mixed-waste (radioactive and hazardous components) that can not be treated for disposal. In this paper we describe a new and unique procedure for the recovery of hafnium radioisotopes from a highly radioactive, proton irradiated, tantalum target using reagents that do not contribute a hazardous waste component.

Chemistry and Concept for an Automated 72Se/72As Generator

The growth of positron emission tomography (PET), with its unique capability to image function as well as structure, depends very much on the availability of positron emitting radioisotopes. Arsenic-72 is a radionuclide possessing significant potential as a PET radioisotope. A wide variety of bone, brain, and tumor seeking agents can be labeled with 72As. A 72Se/72As radiochemical generator would allow on-site recovery of high specific activity 72As for PET research and applications. We have developed a reliable, simple separation chemistry which could be neatly automated for a safe, easy-to-use generator.

Electrolytic separation of selenium isotopes from proton irradiated RbBr targets

Abstract An electrochemical method has been developed to separate selenium isotopes from the spallation products induced in RbBr targets by 800-MeV protons. The selenium isotopes were electrolytically deposited as copper(I) selenide at the surface of a platinum gauze electrode. The copper(I) selenide was then chemically stripped from the electrode in an oxidizing acid environment. This solution was evaporated to soft dryness. The condensate was brought up in 0.1 F HCl and passed through a cation exchange column. Recoveries of better than 80% were obtained.