Volume 94, Issue 2 -

Fission neutron spectrum averaged cross sections of some threshold reactions like ( n , p ), ( n , α) and ( n ,2 n ) on zinc were measured using the activation technique in combination with radiochemical separations and high-resolution γ-ray spectroscopy. Special attention was paid to the formation of 64 Cu via the 64 Zn(n,p) 64 Cu reaction since 64 Cu labeled compounds are potentially important radiopharmaceuticals. At a fast neutron flux density of 7.5 × 10 13 cm -2 s -1 and using a 100% enriched 64 Zn target, 35 GBq activity of no-carrier-added 64 Cu per batch could be produced. The process seems to be interesting from the medical application viewpoint, if a cyclotron is not available. A fast neutron source, on the other hand, would lead to significantly higher yield of 64 Cu.

The interaction of Np(V) with all isomers of pyridinemonocarboxylic acid has been investigated, stability constants have been calculated using NIR spectroscopy. Single crystals of [NpO 2 (Pic)(H 2 O) 2 ] ( 1 ), Cs[NpO 2 (Pic) 2 (HPic)]·3H 2 O ( 2 ), [NpO 2 (Nic)(H 2 O)] ( 3 ), and [NpO 2 (iso-Nic)(H 2 O)] ( 4 ) have been synthesized. Compound 1 contains infinite chains; compound 2 consists of isolated Cs + , [NpO 2 (Pic) 2 (HPic)] - groups and water molecules. In both 3 and 4 neptunoyl-ion NpO 2 acts as monodentate ligand with one of the O atoms of NpO 2 group entering in coordination polyhedron of the adjacent Np atom. Compounds 3 and 4 have layered and three-dimensional topologies, respectively. Crystallographic data: [NpO 2 (Pic)(H 2 O) 2 ], space group P ¯1, triclinic, a = 6.380(2), b = 7.733(2), c = 10.700(4) Å, α = 96.49(3), β = 106.78(3), γ = 103.83(3)°, and Z = 2 ( 1 ); Cs[NpO 2 (Pic) 2 (HPic)]·3H 2 O, space group P ¯1, triclinic, a = 8.707(2), b = 9.777(2), c = 14.640(3) Å, α = 76.633(15), β = 78.75(2), γ = 86.55(2)°, and Z = 2 ( 2 ); [NpO 2 (Nic)(H 2 O)], space group P 2 1 / n , monoclinic, a = 11.901(4), b = 5.5628(15), c = 12.124(3) Å, β = 101.05(2)°, and Z = 4 ( 3 ); [NpO 2 (iso-Nic)(H 2 O)], space group P 2 1 2 1 2 1 , orthorhombic, a = 5.742(3), b = 8.550(5), c = 18.512(10) Å, and Z = 4 ( 4 ). Electron and IR spectra of solid compounds have been measured.

Fungi have up to now generally been used as bioindicators of radiocaesium in terrestrial ecosystems. However there is little knowledge about the behaviour of other man-made radionuclides. In the present work, we analyzed the soil-to-fungi transfer of 90 Sr, 239+240 Pu, and 241 Am by collecting several species of fungi and the corresponding surface soil (0−5 cm) of a selected semi-natural ecosystem. The transfer of these radionuclides was then quantified by means of the traditional transfer factor, TF, defined as the ratio between the content in the fruiting bodies and in the total fraction of soil. As a general rule, the 90 Sr TF values were higher than those of 239+240 Pu and 241 Am. This definition of the transfer factor can underestimate the transfer of radionuclides of which a large percentage are bound to soil particles. We therefore also used a definition based on the amount of radionuclide available to be transferred instead of the total content of the soil — the available transfer factor, ATF — which would be closer to the actual process of transfer. Hebeloma cylindrosporum and Lycoperdon perlatum presented 239+240 Pu and 241 Am ATF values that were greater than or similar to those of 90 Sr. These species may thus be used as bioindicators for 239+240 Pu and 241 Am in a forest ecosystem.

The thermodynamic parameters of formation of the o -silicate complexes of UO 2 2+ , Cm 3+ and Eu 3+ have been measured in the temperature range 5−45 °C in an aqueous medium of 0.20 M NaClO 4 ) ionic strength. Solvent extraction with bis(2-ethylhexyl) phosphoric acid (HDEHP) was used to measure the stability constant (log β 1 ) values of the silicate complexes as a function of temperature to obtain the enthalpies and entropies of complexation. The complexation reactions are entropy driven and opposed by the enthalpy. These thermodynamic values are consistent with the formation of an inner sphere complex.

Sorption of 241 Am and 137 Cs on ion-exchange resins with different functional groups from complexone solutions in liquid CO 2 was investigated. It was shown that more than 99% of radionuclides could be recovered from liquid CO 2 by using strongly acidic resins or H 2 C 2 O 4 ·2H 2 O. Ion-exchange capacity of KU2-8 (analog of DOWEX-50-8) in liquid CO 2 was estimated.

The stabilities of the technetium polymers Tc 2 OCl 10 4− and Tc n O y 4n−2y+ have been studied under light irradiation in 3 M chloride media with a pH range from 0 to 1.3. It has been shown that under irradiation, Tc 2 OCl 10 4− is not stable and undergoes dissociation to TcCl 5 (H 2 O) - at pH = 0 and pH = 0.3. At pH = 1, irradiation of Tc 2 OCl 10 4− leads to a stationary state involving TcCl 5 (H 2 O) - and Tc 2 OCl 10 4− . At pH = 1.3, Tc n O y 4n−2 y+ remains stable under irradiation. Under light irradiation, the predominance diagram of Tc(IV) species obtained from Tc 2 OCl 10 4− aquation in a pH range from 0 to 1 is drawn. The chemical behaviour of Tc 2 OCl 10 4− and the influence of the light on the condensation of Tc(IV) and solubility of TcO 2 · x H 2 O are discussed.

Bentonite has attracted great interest in nuclear waste management because of its outstanding properties. Herein, the sorption and complexation of cobalt on bare bentonite and fulvic acid (FA) coated bentonite are studied, respectively, under ambient conditions. The experiments are carried out at T = 25 ± 2 °C in 0.01 M KNO 3 solutions. Effect of pH, bentonite concentration, fulvic acid and cobalt solution concentration on cobalt sorption to bentonite is also investigated. The results show that cobalt sorption is strongly pH dependent and weakly bentonite content dependent. The presence of fulvic acid enhances Co 2+ sorption at low pH values and reduces the sorption of Co 2+ at high pH values. Effect of addition sequences of Co 2+ and FA to bentonite suspension on cobalt sorption to FA-bentonite colloids is also studied and the results indicate that the sorption of cobalt on FA coated bentonite is dependent on the addition sequences. The mechanism is discussed by the relative strength between both complexes of Co(II) with sorbed and soluble FA and with bentonite.

Autoradiolysis of extraction systems sometimes occurs during reprocessing of spent fuel, which may result in a change in the extraction behaviour of the system. In the work reported here, an aromatic heterocyclic nitrogen bearing tridentate extraction agent, 2,6-di(5,6-diethyl-1,2,4-triazin-3-yl)pyridine (a BTP), was irradiated using a 60 Co source. The investigation focused on the effect of changing the organic diluent in the extraction system in order to protect the extracting agent from degradation. A relationship between the distribution ratio and extracting agent concentration was determined, and it was found that the extraction efficiency decreased with increasing irradiation dose. The effect on extraction of the degradation products from the organic diluents was also considered.

The radioactive concentrations of 99m Tc/ 188 Re from their generators are dependent upon the specific activity of 99 Mo/ 188 W, which dictates the bed size of the alumina/gel column and the volume of physiological saline needed as eluent. Because of the high content of inactive molybdenum/tungsten in neutron irradiated MoO 3 /WO 3 , large columns containing alumina/gel are needed to produce chromatographic 99 Mo → 99m Tc/ 188 W → 188 Re generators. This results in large elution volumes containing relatively high 99 Mo/ 188 W contents and low concentrations of 99m Tc/ 188 Re. The decrease in radioactive concentration, or specific volume, places a limitation on some of the clinical procedures. We report post elution concentration of 99m Tc/ 188 Re using in house prepared silver cation exchange and alumina column. The high bolus volumes (10 − 60 ml saline) can conveniently be concentrated in 1 ml of saline. This approach also works very effectively to yield high specific volume solutions of 99m Tc-pertechnetate from a fission 99 Mo loaded alumina generator towards the end of its normal working life.

Copper-61 (T 1/2 = 3.33 h) produced via the nat Zn( p , x ) 61 Cu nuclear reaction using natural zinc target, was separated from the irradiated target material by a two-step method developed in our laboratory and was used for the preparation of [ 61 Cu]-pyruvaldehyde- bis (N 4 -methylthiosemicarbazone) ([ 61 Cu]-PTSM) using an in house-made PTSM ligand. An electroplated natural zinc layer on a gold-coated copper backing (zinc and gold layer thicknesses were 80 and 50 μm respectively) was irradiated with 22 MeV; protons (22−12 MeV; on the target). 61 Cu was separated by a two-step chromatography method using a cation and an anion exchange column which gave satisfactory results. After 180 μA irradiation of the target for 3.2 hours, about 6.006 Ci of 61 Cu 2+ was obtained with a radiochemical separation yield of more than 95% and a radionuclidic purity of more than 99% ( 60 Cu as impurity). Colorimetric methods showed that traces of chemical impurities in the product were below the accepted limits. The solution of [ 61 Cu]-PTSM was prepared with a radiochemical yield of higher than 80%, radiochemical purity of better than 98% and specific activity of about 246 Ci/mmol.

The dopamine D 4 receptor is hypothesized to relate with the pathophysiology and pharmacotherapy of schizophrenia while its level in brain regions is much lower and to date no suitable tracer is available for the study of D 4 receptor in vivo . Therefore, selective imaging agents for the D 4 subtype are badly needed. Based on the structure-activity analysis of chromeno[3,4-c]pyridin-5-ones as dopamine D 4 receptor ligands, two fluorine-18 labelled chromeno[3,4-c] pyridin-5-one derivatives, 3-(4-[ 18 F]fluorobenzyl)-8-hydroxy-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one and 3-(4-[ 18 F]fluorobenzyl)-8,9-dimethoxy-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one were synthesized through a two-step one-pot method. Their radiochemical yields were around 19.7% (decay-corrected) and radiochemical purities were higher than 95% with specific activities of about 120 GBq/μmol.