The study of conditions for the preparation and application of99Mo−99mTc generators starting from irradiated molybdenum metal

⁹⁹Mo−^99mTc generators were prepared starting from irradiated molybdenum metal instead of MoO₃ in order to use reactor irradiation space more economically. The adsorption of molybdenum as sodium molybdate on different kinds of alumina was investigated. The effect of the pH of the column and the aqueous phase concentration of molybdenum were studied and related to the elution yield of^99mTc. A study of the radiation damage effect indicated that generators having a high elution efficiency of 90% could be prepared in the 100–600 mCi range. The losses of⁹⁹Mo were minimized to 10⁻⁵-10⁻⁴% and those of alumina to 2–5 μg/ml eluate.     

Separation of Tc(VII) from Tc(IV) by solvent extraction

The solvent extraction of Tc(IV) and Tc(VII) by isoamyl alcohol has been studied. The TcCl ₆ ²⁻ and TcO ₄ ⁻ ions are both extracted from 3M H₂SO₄ solution but hydrolyzed Tc(IV) species are not. This permits the separation of the two valence states of technetium. The air oxidation of carrier-free hydrolyzed^99mTc(IV) may be limited by the presence of⁹⁹Tc carrier in the same chemical form. Paper chromatography and electrophoresis were used to identify TcCl ₆ ²⁻ , TcO ₄ ⁻ and hydrolyzed species. It was also found that the hydrolyzed ReCl ₆ ²⁻ can reduce TcO ₄ ⁻ to Tc(IV).     

Synthesis and preliminary biological evaluation of [<Superscript>99m</Superscript>Tc(CO)<Subscript>3</Subscript>(IDA–PEG<Subscript>3</Subscript>–CB)]<Superscript>−</Superscript> for tumor imaging

This work reports the synthesis, radiolabeling and preliminary biodistribution results in tumor-bearing mice of [^99mTc(CO)₃(IDA–PEG₃–CB)]⁻. The novel chlorambucil derivative was successfully synthesized by conjugation of iminodiacetic acid (IDA) to chlorambucil via a pegylated linker. The ligand could be labeled by [^99mTc(CO)₃]⁺ core in high yield to get [^99mTc(CO)₃(IDA–PEG₃–CB)]⁻, which was very hydrophilic and was stable at room temperature. Biodistribution studies in tumor-bearing mice showed that [^99mTc(CO)₃(IDA–PEG₃–CB)]⁻ accumulated in the tumor with favorable uptake and retention. The good accumulation in tumor tissue with high tumor/muscle ratios warrants further research to improve tumor targeting efficacy and pharmacokinetic profile of radiolabeled chlorambucil derivative by structural modification.     

A novel electrochemical <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generator

A novel electrochemical process to avail clinical grade ^99mTc from (n,γ)⁹⁹Mo has been demonstrated. The electrochemical parameters were optimized to maximize the ^99mTc yield with minimal ⁹⁹Mo contamination. ⁹⁹Mo/^99mTc generators containing up to 29.6 GBq (800 mCi) ⁹⁹Mo were developed and their performance were extensively evaluated for 10 days without changing the operating conditions. Very high radioactive concentration of ^99mTcO₄ ⁻ of acceptable quality, commensurate with hospital radiopharmacy requirements could be availed from the system with >90% yield. The compatibility of the product for the formulation of ^99mTc labeled radiopharmaceuticals such as ^99mTc-DMSA and ^99mTc-EC was found to be satisfactory in terms of high labeling yields. The proposed route represents an important step for enhancing the scope of accessing clinical grade ^99mTc from low specific activity (n, γ)⁹⁹Mo.     

Synthesis and biological evaluation of <Superscript>99m</Superscript>Tc-HEDTA/HYNIC-MPP4 complex for 5-HT<Subscript>1A</Subscript> receptor imaging

5-HT_1A receptor is associated with a variety of pathophysiology of neuropsychiatric disorders. Accordingly, we have synthesized a new 5-HT_1A receptor ligand (HYNIC-MPP4) and labeled it with ^99mTc using N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) as coligand. ^99mTc-HEDTA/HYNIC-MPP4 was prepared under pH 6 at room temperature. Biodistribution of 99mTc-HEDTA/HYNIC-MPP4 in normal mice showed that this complex had moderate brain uptake (0.60% ID·g⁻¹ at 2 min p.i.) and good retention. The hippocampus had the highest radioactivity uptake at 2 min p.i. (1.84% ID⋆g⁻¹). The ratio of Hipp/CB was 3.1 at 2 min p.i. and increased to 4.4 at 60 min p.i. After blocking with 8-hydroxy-2-(dipropylamino) tetralin, the uptake of hippocampus was decreased significantly from 1.84% ID·g⁻¹ to 0.53% ID·g⁻¹ at 2 min p.i., while the cerebellum had no significant decrease. This ^99mTc complex could be a potent agent for 5-HT_1A receptor imaging. Supported by the National Natural Science Foundation of China (Grant No. 20401004) and the Analysis and Test fund of Beijing Normal University     

Structural studies on some antimonate exchangers

The possibility of simultaneous extraction of palladium and technetium from nitrate solutions was investigated using tri-n-octylamine (TOA) solutions in carbon tetrachloride as a heavy, non-flammable diluent. Conditions of technetium extraction being essentially known, the main attention was focussed on the extraction of palladium which was studied in dependence on the concentration of nitric acid, salts (nitrates, chlorides, nitrites), urea and palladium. A strong decrease of Pd extraction with 10% TOA in CCl₄ has been found above a palladium concentration of 10⁻⁴M but in the presence of chlorides and nitrites a satisfactory high distribution can be preserved. Both Tc and Pd extracted with TOA/CCl₄ can be stripped into dilute ammoniacal solutions. An extraction procedure for the simultaneous isolation of Pd (80% yield) and Tc (99%) from fission product waste solutions (0.20 g Tc and 0.17 g Pd/dm³ 0.5–1.0M HNO₃) is proposed.     

Determination of technetium-99 from the aspect of environmental radioactivity

A radioanalytical procedure has been developed for the determination of⁹⁹Tc in environmental samples. The procedure consists of precipitation, solvent extraction, ion exchange, electrodeposition and radiation measurement. Rhenium was used as a non-isotopic carrier of⁹⁹Tc. On the basis of 3σ counting error, the detection limits were 4.9·10^?5 Bq/l, 7.4·10^?3 Bq/kg wet and 7.4·10^?2 Bq/kg dry for water, biota and soil samples, respectively. Sea water, seaweeds (brown algae) and soils were collected to evaluate the present levels of⁹⁹Tc in Japan. The level of⁹⁹Tc in sea water was ca. 1·10^?4 Bq/l around Japan. Among the seaweeds (brown algae), Ishige okamurai showed the highest concentration of 5.8·10^?2 Bq/kg wet tissue and the highest concentration factor of 583. The level of⁹⁹Tc in the organic rich surface soil was ca. 1 Bq/kg dry soil in Fukuoka.     

Determination of alpha and pure beta emitting impurities in99Mo/99mTc generator eluates

The determination of α- and pure β-emitting impurities in⁹⁹Mo/^99mTc generator eluates before application is discussed. It is shown that α-emitters in ≥10 mCi eluates can be determined in a proportional counter or an α-spectrometer within 30 min with detection limits lower than the European Pharmacopoeia limit (10⁻⁷% of the main activity).⁸⁹Sr and⁹⁰Sr are determined after chemical separation, consisting of ion exchange to separate the main activity (TcO ₄ ⁻ ), shaking with charcoal to separate colloidal particles containing Mo and precipitation of Sr as oxalate or sulfate. The precipitate is measured in a low-level counter. For eluates with an activity of ≥10 mCi the detection limits are one order of magnitude lower than the activity limit given by the European Pharmacopoeia for⁹⁰Sr (6×10⁻⁶% of the main activity). The time needed for chemical separation and activity measurement is about 30 min.     

Technetium-99 in “instant”99mTc-pertechnetate

The⁹⁹Tc-content in^99mTc-pertechnetate separated from⁹⁹Mo by distillation or extraction has been studied with a plastic scintillation detector. The identification of the measured activity was achieved by beta-spectrometry, chemical separation and half-life studies. The frequency distribution of the⁹⁹Tc/^99mTc-ratios in the different samples was observed to be log-normal. The most likely activity ratio was 0.4·10⁻⁶, the maximum value being 5·10⁻⁶. The specific activity of “instant” pertechnetate is approximately a factor of 60 lower than that normally recorded in pertechnetate derived from daily eluted column generators. The low specific activity of “instant” pertechnetate is primarily explained by the long time between separation and usage and secondly by the low yield of Tc in the distillation and extraction processes. In several of the “instant” pertechnetate solutions the carrier concentration exceeded the reductive capacity of the stannous ions in “kits” with small amounts of Sn(II) in usable form.     

Promotion of the lower limit of detection of gamma emitting nuclides in radioaerosol samples after Fukushima accident

Through placement in a few hours after collecting radioaerosol samples (in Shanghai) after Fukushima nuclear power plant (NPP) accident, radionuclides with gamma-emitting rays can be found to be nuclides (¹³²I/¹³²Te, ¹²⁹I/¹²⁹Te) other than ¹³¹I, ^134,137Cs because of the decrease in background baseline after the daughter nuclides (i.e. ²¹⁴Bi, ²¹⁴Pb and etc.) of radon makes decay sharply. Based on aerosol sample collected by passing through 1,300 M³ air in 24 h, the lower limit of detection (LLD) of ¹³²I/¹³²Te, ¹²⁹I/¹²⁹Te can be decreased from 6.11 × 10⁻⁵, 3.46 × 10⁻⁴ Bq m⁻³ after half an hour sampling to 1.64 × 10⁻⁵, 8.19 × 10⁻⁵ Bq m⁻³ after sampling 48 h sampling. Similarly, LLD can be decreased from 9.63 × 10⁻⁵ to 1.41 × 10⁻⁵ Bq m⁻³ for ¹³¹I, 7.72 × 10⁻⁵ to 9.96 × 10⁻⁶ Bq m⁻³ for ¹³⁴Cs and 9.67 × 10⁻⁵ to 1.45 × 10⁻⁵ Bq m⁻³ for ¹³⁷Cs after the same time sampling. In the same time, the activities of daughter nuclides such as ²¹⁴Pb and ²¹²Bi from the decay of their parent nuclides ²²²Rn and ²²⁰Rn can sharply decrease from 2.45 × 10⁻², 2.57 × 10⁻² Bq m⁻³ to be ~10⁻⁴ Bq m⁻³ while the activities of the concerned nuclides ¹³²I/¹³²Te, ¹²⁹Te, ¹³¹I, ^134,137Cs were almost constant. As our knowledge, it is the first time to report such case which is very helpful to monitor the leaked nuclides from NPP by aerosol sampling in both normal operation case and emergency case.     

Further study on NAA in characterizations of reference materials

A program was initiated at Chalk River Laboratories (CRL) to determine the physical, chemical and radiological properties of wastes intended for disposal in IRUS (Intrusion Resistant Underground Structure), a below ground vault to be constructed at CRL. One of the most restrictive radionuclides for IRUS is¹²⁹I, which has been assigned a maximum activity concentration in waste of 10⁶ Bq/m³. The limit of detection for radionuclides in waste has been set at 1% of the approximate maximum activity concentration, or 10⁴ Bq/m³ for¹²⁹I. A radiochemical instrumental neutron activation analysis method has been developed to determine¹²⁹I in two waste streams, incinerator ash and liquid feed to a bituminizer. Solid samples are spiked with¹²⁵I tracer, fused at 960°C with Li₂B₄O₇ in a platinum boat in a flowing oxygen stream inside a three zone tube furnace, and the volatilized I₂ is trapped on in-line charcoal filters. The charcoal filters are irradiated together with a filter containing a spiked¹²⁵I/¹²⁹I standard, in the NRU reactor, and then subjected to post-irradiation chemistry to remove⁸²Br interference. The¹²⁹I concentration in the sample is determined by comparing the activity of the activated¹³⁰I in the sample with that of the standard, and the chemical recovery for¹²⁹I is determined from the activity of¹²⁵I tracer. Limits of detection for¹²⁹I in solids are typically 0.005 Bq/g, based on a 4 hour counting period on a 10% efficient HPGe gamma-spectrometer at a source to detector distance of approximately 12 cm. This paper presents a summary of the method and the results from analysis of two waste streams.     

The interaction of <Superscript>99m</Superscript>Tc with pyrimidine compounds

The reaction of ^99mTc of different oxidation states (+7, +4) with 2-thiouracil and 5-nitrobarbituric acid have been studied at different temperatures, pH and concentrations. The reaction mixtures have been analyzed at different times using thin layer chromatography (TLC) and a radio detector to show the peaks at the plates. ^99mTc is obtained from the Mo generators with oxidation state (+7). The use of SnCl₂ as a reducing agent gave ^99mTc with oxidation state (+4). It is very difficult to separate the complexes formed from the reactions in very small concentration. The percentage of ^99mTc and its oxidation state involved in the complexes can be determined. The labeling efficiencies (percentage of complex) in the reaction of ^99mTc⁺⁷ with 5-nitro-barbituric-acid increases mostly at pH  10. Both oxidation states of ^99mTc(+7, +4) can be detected at pH’s 4 and 10, but at pH  4, the reduced form ^99mTCO₂, is more pronounced. At pH  7 no complexes were detected and most of ^99mTc remains as ^99mTCO₄ ⁻ . By increasing the ligand concentration, the labeling efficiencies of the complex increases. For the reaction of ^99mTc of oxidation states (+4, +7) with 2-thiouracil at different temperatures and analytical times it is concluded that several complexes with different R_f values were observed in equilibrium and most of these complexes were unstable.     

Determination of technetium-99 in soils and radioactive wastes using ICP-MS

Three methods have been used for the determination of ⁹⁹Tc in soils and solid radioactive wastes using ^99mTc as a yield monitor. In the method one and three the samples were leached in low concentrated nitric and sulphuric acid. Many contaminants were then co-precipitated with Fe(OH)₃ in alkali media and Tc in the supernatant was separated using anion-exchange extraction chromatography. There were made also some studies how to improve the chemical recovery of ^99mTc in the process of chromatography. In the method two the sample was ashed and then leached in 8 mol dm⁻³ HNO₃ and after iron precipitation, technetium was separated on chromatographic column. The chemical recovery of ^99mTc was optimized in the process of chromatography and leaching. Typical recoveries of technetium determined with ^99mTc tracer for all these methods were in the range 39 %–87 %. The ⁹⁹Tc activity was measured using proportional low-background beta detector after one week of staying to allow decay of ^99mTc activity. ⁹⁹Tc was also determined by the non-radiometric method using inductively coupled plasma mass spectrometer.     

Exchange labeling of proteins:99mTc labeled transferrin

^99mTc-labeled transferrin was prepared by reduction of^99mTcO ₄ ⁻ ; with stannous DTPA or stannous citrate followed by equilibration of the technetium chelate with human transferrin. The rate of transfer of^99mTc to transferrin in the presence of 0.015M citrate buffer was dependent on pH in the order pH 2.1> pH 7.2> pH 4.1> pH 5.9. The incorporation rate was inversely proportional to the concentration of DTPA and citrate buffer. The replacement of citrate buffer by acetate buffer or oxalate buffer reduced drastically the formation of^99mTc-labeled transferrin at pH 4.1. The formation of^99mTc-labeled transferrin prepared from the reduction of^99mTcO ₄ ⁻ with stannous citrate was faster than that from the reduction with stannous DTPA in the presence of 0.015M citrate buffer and pH 2.5. Equilibration of transferrin with^99mTc-labeled pyrophosphate did not produce^99mTc-labeled transferrin at pH 4.5. The ligand exchange labeling of^99mTc to transferrin in 0.015M citrate did not cause appreciable denaturation of the protein at all pH values. This method also enabled labeling of the protein in a low concentration (2.6·10⁻⁴ M) via tin reduction. Sequential external imaging of the^99mTc-labeled transferrin in Sprague-Dawley rats bearing Walker-256 carcinosarcoma showed optimal tumor localization occurred at 3 hr after injection. In spite of this,^99mTc-labeled transferrin does not appear to be a suitable imaging agent because of the low tumor to blood ratio of^99mTc (0.50±0.17) at 3 hr post injection. This is similar to that of^{6 7}Ga-citrate (0.43±0.15%).     

Iodide interaction with natural pyrite

¹²⁹I is one of the major dose-determining nuclides in the safety analysis of deep storage of radioactive waste. Iodine forms anionic species that hardly sorb on the surfaces of common host-rock minerals. Recently, interest has arisen on the role of pyrite, an accessory mineral capable of binding anionic selenium. Whereas the interaction of selenium with pyrite is well documented, corresponding results on iodine sorption are still scarce and controversial. Pyrite is present in argicilleous rocks which are being considered in many countries as potential host rocks for a radioactive waste repository. The uptake of iodide (I⁻) on natural pyrite was investigated under nearly anoxic conditions (O₂ < 5 ppm) over a wide concentration range (10⁻¹¹–10⁻³ M total I⁻) using ¹²⁵I as the radioactive tracer. Weak but measurable sorption was observed; distribution coefficients (R _d) were less than 0.002 m³ kg⁻¹ and decreased with increasing total iodide concentration. Iodide sorption was connected to the presence of oxidized clusters on the pyrite surface, which were presumably formed by reaction with limited amounts of dissolved oxygen. The results obtained indicated that pyrite cannot be considered as an effective scavenger of ¹²⁹I under the geochemical conditions prevailing in underground radioactive waste geologic storage.     

Two novel procedures of preparation for [Tc(CO)<Subscript>2</Subscript>(NO)]<Superscript>2+</Superscript>labeled by EHIDA and its biodistribution

To develop potential new Tc radiopharmaceuticals, a novel compound [^99mTc(CO)₂(NO)(EHIDA)]⁰ (EHIDA: 2,6-diethylphenylcarbamoylmethyliminodiacetic acid) has been prepared by reacting [^99mTc(CO)₃)(EHIDA)]⁻ with NOBF₄ both in water and acetonitrile. The conversion of [^99mTc(CO)₃)(EHIDA)]⁻ to [^99mTc(CO)₂(NO)(EHIDA)]⁰ was supported by TLC, HPLC and eletrophoresis. The radiochemical purity (more than 99%) was proved by TLC and HPLC. The biodistribution in mice demonstrated that [Tc(CO)₂(NO)(EHIDA)]⁰ showed higher uptake in blood, kidney and lung (15 min, blood: 19.24±2.95; kidney: 13.61±3.49; lung: 10.81±1.09.) but a lower uptake in liver (15 min, 5.73±0.74). The slower clearances (120 min, blood: 12.75±1.34; kidney: 13.61±3.49) from blood and kidney were also found. This research describes two methods for the conversion of [^99mTc(CO)₃]⁺ into [^99mTc(CO)₂)(NO)]²⁺ by using NOBF₄ as the source of NO⁺ both in organic solvent and water. The latter method offers the possibility to introduce the NO-group in high yield in water.     

Separation of no-carrier-added <Superscript>90</Superscript>Nb from proton induced natural zirconium target

Amongst various radionuclides of molybdenum, ⁹⁰Mo and ⁹⁹Mo have suitable β energy for clinical uses. In this paper we report separation of ⁹⁹Mo from ⁹⁹Mo-^99mTc equilibrium mixture. The liquid–liquid extraction technique has been employed using trioctylamine (TOA) diluted in cyclohexane as organic phase and HCl as aqueous phase. At 10⁻⁵ M HCl and 0.5 M TOA concentration ^99mTc quantitatively transferred to the organic phase leaving ⁹⁹Mo in the aqueous phase. The developed separation method is efficient and provides very high separation factor.     

Separation of strontium from calcium by the use of sodium hydroxide and its application for the determination of long-term background activity concentrations of <Superscript>90</Superscript>Sr in 100 km area around Kozloduy Nuclear Power Plant (Bulgaria)

The method for the determination of ⁹⁰Sr which employs sodium hydroxide for the separation of strontium from calcium was further improved introducing the use of elevated temperatures. The results from 11-year study of background activity concentrations of ⁹⁰Sr in different environmental objects in 100 km zone around Kozloduy Nuclear Power Plant (Bulgaria) are presented as an application of the analytical method. The measured mean values are as follows: air precipitation − 0.0015±0.0009 Bq(m^2.d), tap water − 0.0017±0.0012 Bq/L, soil − 1.90±1.26 Bq/kg, grass − 1.54±0.80 Bq/kg, milk − 0.023±0.012 Bq/L and for the Danube river: water − 0.0046±0.0026 Bq/L, bottom sediments − 0.64±0.60 Bq/kg, algae − 1.99±1.56 Bq/kg. The calculated transfer coefficients (soil-grass) are in the range of 0.33–0.84. Between 2 and 5 times reduction in actual background activities of ⁹⁰Sr is observed compared to 1972–1974.     

Characterization of the reduction products of99TcO 4 − with stannous ions in citrate solutions

The chemical state of the products of⁹⁹TcO ₄ ⁻ reduction by Sn(II) in citrate media has been investigated using electrochemical methods. The Tc(V) chelates formed after consumption of one mole Sn(II)/g-atom TcO ₄ ⁻ were identified as oxo(biscitrato)technetates(V) existing in different coordination isomers. Their reduction products were hydroxo (biscitrato)technetates(IV). The products proved to be the same as reported in the case of the electrochemical reduction of TcO ₄ ⁻ in citric acid.     

Verflüchtigung von Radionukliden im Luftstrom und Ihre Abscheidung im Temperaturgradientrohr

The Hg-, Cd- and UO₂-targets bombarded by protons have been treated using the sublimation and evaporation techniques. The Hg and Cd nuclei have been separated from non-isotopic products by distillation in the hydrogen stream. The separation of the groups of Re, Os, Ir, Mo, Tc and Ru oxides has been carried out in the air stream. No monotonic temperature dependence of the Tl, Ru, Mo, Tc, Te, Pb and Po release has been observed in the oxidation of the UO₂-ceramics in the air stream. The values of (−ΔH _a ⁰ ) of volatile products adsorbed on quartz have been determined from the chromatographic data. The relation between the adsorption heat (−ΔH _a ⁰ ) and the standard sublimation heat (ΔH ₂₉₈ ⁰ subl.) has been found to be linear, i.e. −ΔH _a ⁰ =(4.04±1.97)+(0.69±0.04)ΔH ₂₉₈ ⁰ (subl.). As an example of the thermochromatographic generator of isotopes, the separation of⁹⁹Mo to^99mTc has been investigated.