Monitoring of Radionuclide Impurities in <Superscript>166</Superscript>Ho-Albumin Microspheres Prepared by Neutron Activation with Thermal Neutrons

Analysis of radionuclide impurities in ¹⁶⁶Ho-albumin microspheres prepared by activation with thermal neutrons of ¹⁶⁵Ho preliminarily incorporated in the particle matrix was performed. The content of impurities in the final product was determined by γ-ray spectroscopy. With ¹⁶⁶Ho-albumin microspheres as example, an algorithm was developed for evaluation of the radiochemical purity of the preparation. It was found that the radiochemical purity of the preparation, which is primarily determined by impurities of rare-earth elements, can be estimated from the content of ^152m Eu.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 278–280.Original Russian Text Copyright © 2005 by Petriev, Skvortsov, Smakhtin, Shutova.     

Recovery of <Superscript>131</Superscript>I and <Superscript>137</Superscript>Cs from a solution simulating NPP trap waters

Sorption of ¹³¹I and ¹³⁷Cs from a solution simulating NPP trap waters on various inorganic and organic sorbents was studied. The highest degree of ¹³¹I recovery (>99%) can be attained with Fizkhimin granulated sorbents based on coarsely porous silica gel containing Ag and Ni in 1: 4 ratio, with K _d for ¹³¹I exceeding 10⁵ ml g⁻¹ at V/m = 10³ ml g⁻¹ and contract time of the solid and liquid phases of 120 min. Elevation of the solution temperature to 40°C does not affect the degree of ¹³¹I and ¹³⁷Cs recovery. The degree of ¹³⁷Cs recovery in all the experiments did not exceed 35%. The degree of ¹³¹I recovery by coprecipitation with AgCl and Ag₄[Fe(CN)₆] was about ∼96% and only 65%, respectively.     

Extraction centrifugal generator of <Superscript>188</Superscript>Re and radiopharmaceuticals based on it for radionuclide therapy

The results of the development of a medical-purpose extraction ¹⁸⁸Re generator and of ¹⁸⁸Re radiopharmaceuticals are presented. The main advantage of this generator is the possibility of using as starting material tungsten oxide of natural isotope composition, irradiated in a reactor with medium neutron flux [(1.0–1.4) × 10¹⁴n cm^–2 s^–1]. Separation of the parent ¹⁸⁸W and daughter ¹⁸⁸Re was performed in a centrifugal semicounter-current contactor developed at the Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences. The ¹⁸⁸Re yield is about 90%, and the radiochemical purity (Na¹⁸⁸ReO₄ content) is ≥95%. The content of the ¹⁸⁸W impurity is less than 1 × 10^–3% relative to the ¹⁸⁸Re activity, and the content of other radionuclides is less than 1 × 10^–4%. The resulting Na¹⁸⁸ReO₄ solution was registered as “Active pharmaceutical substance” and was used in the development and subsequent preclinical trials of several radiopharmaceuticals for radionuclide therapy of pain syndrome accompanying the development of cancer metastases into the skeleton, and also for radiosynovectomy.     

Preparation and properties of <Superscript>68</Superscript>Ga complexes with RGD peptide derivatives

Conditions allowing preparation of ⁶⁸Ga complexes with RGD peptide derivatives with no less than 95% radiochemical purity were determined. The complexes are stable in blood plasma for the time sufficient for performing a diagnostic investigation.     

Preparation and quality control of <Superscript>32</Superscript>P-labeled albumin particles for internal radiotherapy

The paper deals with the preparation and quality control of ³²P-labeled albumin particles used in therapy of inoperable solid tumors with remarkable vascularization. A process was developed for preparing ³²P-labeled albumin particles by combining biocompatible human serum albumin and [³²P]phosphoric acid salt. Factors affecting the process were investigated, and labeling conditions were optimized. The size distribution, shape, and radiochemical stability of particles were determined. The biodistribution of the particles was examined after intravenous injection in Wistar rats. The in vivo stability and distribution of the radioactive particles in mice were studied with different administration methods. Optical microscopic examinations revealed that the particles had a narrow size distribution (20–50 μm) after sterilization and dispersion in a mixture of normal saline and human serum albumin or in Tween 80 solution. The particles prepared had high radiochemical stability and 99% purity. Experiments on the distribution in animals showed that high radioactivity was accumulated in the lungs as a vascular tumor model.     

<Superscript>210</Superscript>Ро in black and green teas

The ²¹⁰Ро content in various grades of tea sold in St. Petersburg shops was determined, and the effective annual dose of internal irradiation from ²¹⁰Ро at daily tea drinking was estimated. As shown by α-ray spectrometry, the activity concentration of ²¹⁰Ро in tea leaves varies from 1.1 to 25 Bq kg^–1. The ²¹⁰Po content in black teas is, on the average, 1.7 times higher than in green teas. This difference is accounted for by specific features of processes for the production of black and green teas. From 1.5 to 56% of ²¹⁰Ро passes into aqueous extracts. Despite higher polonium content in black teas, the amount of ²¹⁰Po extracted from green teas is, on the average, 6.3 times higher than that extracted from black teas. This effect may be associated with the formation of water-soluble organic polonium compounds on the surface of tea leaves in the course of tea processing. The effective annual dose of internal irradiation from polonium at daily use of 10 g of dry tea is estimated at 0.8–9.5 μSv year^–1 depending on the tea grade, or 0.5–5.8% of the average annual dose of irradiation of the Russian Federation population from the sum of the nuclides (²¹⁰Pb, ²¹⁰Po, ²²⁸Rа, ²²⁶Rа, etc., except ⁴⁰K) getting into a human body with food and water.     

Sorption of Mo(VI) on zirconium molybdosilicate gel and potential application as a <Superscript>99</Superscript>Mo/<Superscript>99<Emphasis Type="Italic">m</Emphasis> </Superscript>Tc generator

Sorption of Mo(VI) from aqueous nitrate solutions onto zirconium molybdosilicate (ZrMoSi) gel was studied using ⁹⁹Mo radiotracer. The acid–base titration curve showed that the prepared ZrMoSi gel was an amphoteric material with the point of zero charge (PZC) at pH 2.5. The highest distribution coefficient (600 mL g^–1) of ⁹⁹Mo(VI) on ZrMoSi from nitrate media was achieved at pH 2.1. The sorption kinetics of ⁹⁹Mo(VI) onto ZrMoSi obeyed the pseudo-second-order model. The breakthrough sorption capacity of ZrMoSi gel was found to be 4.25 × 10^–2 [mmol Mo(VI)] g^–1. The prepared ⁹⁹Mo/^99mTc chromatographic column generator showed a good performance: The ^99mTc elution yield was 87.7%, pH of the eluate ranged from 5.6 to 7.2, and the radionuclidic purity of the eluted ^99mTc was >99.99% with a radiochemical purity of 98.31% (as ^99mTcO₄^–).     

Prospects for using reactor palladium for <Superscript>129</Superscript>I immobilization

The efficiency and application prospects of various methods for Pd recovery from solutions of various compositions are reviewed. Particular attention is given to the problem of the recovery of reactor Pd with the aim of its use for reprocessing of radiochemical production wastes (e.g., for immobilization of ¹²⁹I and/or TPE). The results of experiments on the synthesis of Pd-based formulations incorporating PdI₂ are described. Incorporation of ¹²⁹I into a Pd matrix allows preparation of a material with a low leach rate, suitable for long-term safe storage.     

A modified electrochemical procedure for isolating <Superscript>177</Superscript>Lu radionuclide

A cell for isolating ¹⁷⁷Lu from a neutron-irradiated ¹⁷⁶Yb target was developed. The procedure involves a combination of two processes: contact reduction of Yb from acetate–chloride solution on sodium amalgam, followed by electrolysis of the solution on a mercury cathode. The process conditions were chosen so that the adjustment of the working solution characteristics (composition, pH, etc.) in going from contact reduction to electrolysis was not required. Both processes are performed in one cell, which reduces the ¹⁷⁷Lu loss. On an installation consisting of two cells, the decontamination factor of the ¹⁷⁷Lu solution from Yb of up to 10⁶ was reached, which is necessary for obtaining a ¹⁷⁷Lu preparation of high specific activity.     

Asymmetric synthesis of 6-<Superscript>18</Superscript>F-<Emphasis Type="Italic">L</Emphasis>-FDOPA using chiral Nickel(II) complexes

A new procedure was suggested for asymmetric synthesis of of 6-[¹⁸F]fluoro-3,4-L-dihydroxyphenylalanine (6-¹⁸F-L-FDOPA), an important radiotracer for studies of the dopaminergic system by positron emission tomography (PET). The key step of the synthesis is stochiometric asymmetric alkylation of chiral Ni(II) complexes using 3,4-methylenedioxy-6-[¹⁸F]fluorobenzyl bromide as alkylating agent. A series of Ni(II) complexes containing various substituents in the benzyl group were tested. The highest enantiomeric purity of 6-¹⁸F-L-FDOPA was attained with the complex derived from (S)-N-(2-benzoylphenyl)-1-(3,4-dichlorobenzyl)-pyrrolidine-2-carboxamide, Ni-DCBPB-Gly, under mild alkylation conditions (CH₂Cl₂, 40°C, potassium tert-butylate as base). Such conditions are favorable from the viewpoint of synthesis automation. The radiochemical yield of 6-¹⁸F-L-FDOPA corrected for the radioactive decay was 10–15% at a synthesis time of 120 min, including purification by semipreparative HPLC. The radiochemical and chemical purity of the product exceeded 99%, and the enantiomeric purity was as high as 95%, meeting the requirements for using 6-¹⁸F-L-FDOPA in PET practice.     

Synthesis of <Superscript>177</Superscript>Lu-based bioconjugate for radioimmunotherapy and evaluation of its stability in physiological media

Labeling of the conjugated molecule of human serum albumin (HSA) and humanized scFv 4D5 mini-antibody specific to her-2/neu receptor with β-emitting ¹⁷⁷Lu radionuclide via p-SCN-benzyl-DTPA chelator was studied. The radioconjugate can be prepared with the decay-corrected radiochemical yield of 82%. The stability of the synthesized complex in physiological solutions (normal saline, human blood serum) was evaluated. The complex is stable in physiological solutions for no less than 10 days.     

Development of Diffusion-Thermal Methods for Preparing <Superscript>67</Superscript>Cu and <Superscript>124</Superscript>I for Radionuclide Therapy and Positron Emission Tomography

Diffusion-thermal procedures for preparing ⁶⁷Cu and ¹²⁴I for radionuclide therapy and positron emission tomography are suggested. For these procedures, new cyclotron targets of metallic tantalum were developed, which, when exposed to high irradiation doses, ensure the absence of physicochemical interaction (diffusion, alloying) of materials being activated and final products with the support at high temperatures. The thermal, hydrodynamic, and strength characteristics of zinc and tellurium (elemental Te) cyclotron targets were evaluated. For commercial target assembly of the COSTIS system, the operation parameters of the process for preparing ¹²⁴I from elemental tellurium using the derived beams of IBA Cyclone 18/9 or MGTs- 20 accelerators were determined.     

Radionuclide Diagnostics of the Sorption Using the <Superscript>224</Superscript>Ra Subfamily and α-Ray Spectrometry

A method was suggested for radionuclide diagnostics of the sorption using the ²²⁴Ra subfamily and α-ray spectrometry. The method allows the diffusion in transport pores to be distinguished from the diffusion in a regular crystalline body. The possibilities of the method were illustrated by the example of a system consisting of a thin layer of manganese hydroxide deposited on three different kinds of support (cellulose triacetate, polyethylene, polyimide 66 in the form of flat discs 24 mm in diameter) and an aqueous ²²⁴Ra solution. A joint study of the kinetics of the Ra sorption and characteristics of α-ray spectra of samples of ²²⁴Ra sorbed onto thin-layer manganese hydroxide and of its daughter radionuclides (energy resolution and emanating ability of α-ray sources) allows the steps of external diffusion in a laminar liquid flow on the surface of sorbent granules, diffusion in transport pores, and diffusion in a regular crystalline body to be clearly distinguished in time.     

Radioactivity calculations for production of <Superscript>131</Superscript>I by neutron irradiation of tellurium targets

The radioactivity of ¹³¹I as well as of the other radioisotopes, obtained from different nuclear reactions occurring during irradiation of natural tellurium including different decay branches, at the end of irradiation and after different cooling times was calculated. The optimum cooling time is 90 h. Published in Russian in Radiokhimiya, 2009, Vol. 51, No. 3, pp. 275–281. The text was submitted by the author in English.     

Gas-Phase UV Photolysis of CH<Subscript>3</Subscript><Superscript>131</Superscript>I

Gas-phase UV photolysis of ¹³¹I-labeled CH₃I was studied. CH₃ ¹³¹I (228 mg) is completely photolyzed within 5 min under the static conditions at room temperature in an argon atmosphere. The final radioiodine compound formed under these conditions is ¹³¹I₂. The chemical composition of the final products of CH₃I photolysis in air is more complex. Agglomeration corcystallization of the CH₃I photolysis products with NH₄Cl in the gas phase was studied. The results of this study suggest that the main final product of CH₃I photolysis in air is a fine I_xO_y aerosol. In the presence of NH₄Cl, formation of NH₄ ¹³¹I aerosols is possible.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 269–273.Original Russian Text Copyright © 2005 by Kulyukhin, Kulemin, Rumer, Konovalova.     

Separation of Carrier-Free <Superscript>115<Emphasis Type="Italic">m</Emphasis></Superscript>In from Its Parent <Superscript>115</Superscript>Cd Using the Synthesized TODGA-Impregnated Silica Gel

A radiotracer technique has been used to achieve the carrier-free separation of ^115mIn from its parent ¹¹⁵Cd in hydrochloric acid medium on a chromatographic column packed with TODGA-impregnated silica gel. At 8 M HCl, both cations are bound at the chelating site, which results in maximum adsorption. When the column is treated with 2 M HCl, the daughter complex gets desorbed and is eluted from the column, whereas the parent remains undisturbed. Pure silica gel does not adsorb radioactivity under these conditions. The radiochemical purity of daughter was checked by its half-life (4.49 h).     

Recombination luminescence of CaI<Subscript>2</Subscript> crystals activated with Eu<Superscript>2+</Superscript>, Gd<Superscript>2+</Superscript>, Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript>

The spectral characteristics of thermostimulated luminescence, steady-state roentgenoluminescence and photostimulated luminescence (PSL) buildup and decay kinetics, and the effect of IR irradiation on the roentgenoluminescence yield and glow curves of CaI₂:Eu²⁺, CaI₂:Gd²⁺, CaI₂:Tl⁺, CaI₂:Pb²⁺, CaI₂:Mn²⁺, and CaI₂: Pb²⁺, Mn²⁺ crystals grown by the Bridgman-Stockbarger method have been studied in the temperature range 90–295 K. Coupled with earlier data, the present results on the influence of oxygen and hydrogen impurities on the spectral characteristics of CaI₂ indicate that the activation of calcium iodide with Eu²⁺, Gd²⁺, Tl⁺, Pb²⁺, and Mn²⁺ leads to the formation of cation impurity-native defect complexes, which act as carrier traps and are responsible for the thermostimulated luminescence in the range 150–295 K. IR exposure after 90-K x-ray excitation gives rise to flash PSL and influences the thermostimulated luminescence light sum. The nature of the emission and trapping centers involved and the mechanisms of recombination luminescence excitation in the crystals are discussed.     

High-purity silicon isotopes <Superscript>28</Superscript>Si, <Superscript>29</Superscript>Si,and <Superscript>30</Superscript>Si

The current status of the problem of obtaining high-purity silicon isotopes ²⁸Si, ²⁹Si, and ³⁰Si is analyzed. The scheme of obtaining monoisotopic silicon includes the stages of isotope separation in the form SiF₄, synthesis and deep purification of isotopically enriched silane, obtaining polycrystalline silicon-28,-29, and-30, and growing monocrystals. The basic problems and methods of their solution in the synthesis and deep purification of silane and obtaining poly-and monocrystals of isotopically enriched silicon are discussed. Data characterizing the achieved level of chemical and isotopic purity of high-purity monocrystals of silicon-28 with a main isotope content of more than 99.99% and silicon-29 and silicon-30 with isotopic purity higher than 99% are presented. In monocrystalline ²⁸Si, the boron content was 4.5 × 10¹³, the phosphorus content was 5 × 10¹¹, the carbon and oxygen contents were <1 × 10¹⁶ at/cm³, and the specific resistance was 800 Ω cm. The results of investigation of heat capacity, heat conduction, photoluminescence, and electron paramagnetic resonance spectra for monoisotopic silicon-28 are presented. The heat conduction of monoisotopic silicon is increased considerably owing to the reduced photon scattering on isotopic inhomogeneities. In the region of 20–30 K, the heat conduction of silicon-28 with an isotopic purity of 99.98% is higher by a factor of 8 than the heat conduction of natural silicon. Investigations of photoluminescence spectra in the magnetic field in the low-temperature region demonstrated the capability of optical detection of nuclear spin states of a phosphorus admixture in high-purity silicon-28. p ]Topical questions for further investigations and possible fields of practical application of high-purity isotopically enriched silicon are discussed.     

Reactor production and purification of <Superscript>153</Superscript>Sm radioisotope via <Superscript>nat</Superscript>Sm target irradiation

Neutron irradiation of a natural Sm target is performed to produce ¹⁵³Sm. Ion-exchange chromatography is used to separate ¹⁵³Sm from Eu radionuclides produced in the process. To prepare a target, Sm₂O₃ powder is dissolved in 0.2 ml of HNO₃ in a quartz vial. Samarium is deposited onto the vial walls by passing nitrogen gas at 120°C. The prepared samarium target is encapsulated in aluminum foil and irradiated in a 5-MW reactor in 5 × 10¹³ n cm⁻² s⁻¹ flux. The irradiated target is dissolved in 1 M HCl, and the produced radioisotopes are determined with an HPGe nuclear detector. Finally ¹⁵³Sm is separated from Eu radionuclides with ¹⁵³Sm recovery yield of more than 66% and purity better than 99.8%.     

Isolation of <Superscript>58</Superscript>Co, <Superscript>54</Superscript>Mn,and <Superscript>86</Superscript>Rb from <Superscript>89</Superscript>Sr production wastes

Procedures for isolation of ⁵⁸Co, ⁵⁴Mn, and ⁸⁶Rb from ⁸⁹Sr production wastes are described. The production of ⁸⁹Sr was based on irradiation of natural Y in the form of oxide, placed in 1Cr18Ni10Ti stainless steel ampules, on a BR-10 fast reactor. ⁵⁸Co and ⁵⁴Mn were isolated from the casings of stainless steel ampules, and ⁸⁶Rb, from the tail solution after the isolation of ⁸⁹Sr.