Volume 91, Issue 4 -

Irradiation of nitrogen with protons leads to 11 C ( T 1/2 =20.4min) via the well-known 14 N( p , α ) reaction. However, 14 O ( T 1/2 =70.6s) and 13 N ( T 1/2 =10min) are also formed as side products via the 14 N( p , n ) and 14 N( p , d + pn ) reactions, respectively. In this work detailed cross section measurements were carried out for those two side reactions up to 19.2MeV using N 2 gas and nitrogen-containing solid targets. From the data, the thick-target yields and the exact level of radioactive impurities in 11 C were calculated. In the case of 14 O, the results also confirmed the possibility of producing this β + emitting radionuclide in sufficient quantities for PET investigations.

The adsorption method for determination of the distribution of neptunium among its oxidation states by the use of solvent impregnated resins and bismuth phosphate precipitates as adsorbents is described. For neptunium in concentration ranging from ∼10 -10 to ∼10 -2.5 M, Np(IV) and Np(VI) were quantitatively adsorbed on the impregnated resin in a solution of the acidity 1.0-0.1M HClO 4 , while Np(V) remained in the liquid phase. In the same condition, the precipitate of bismuth phosphate absorbed Np(IV) selectively, leaving Np(V) and Np(VI) in the liquid phase. By carrying out these adsorption methods in Ultrafree-MC Microporous Centrifugal Filter Units (Millipore Corporation), the oxidation state distribution of neptunium in acid solution can be determined in a simple manner with a small sample volume (500μl) regardless of its concentration.

The removal of uranyl nitrate from tissue matrix has been studied with supercritical carbon dioxide modified with methanol alone as well as complexing reagents dissolved in methanol. A systematic study of various complexing agents led to the development of an extraction procedure for the quantitative recovery of uranium from tissue matrix with supercritical carbon dioxide modified with methanol containing small quantities of acetylacetone. The drying time and temperature employed in loading of uranyl nitrate onto tissue paper were found to influence the extraction efficiency significantly.

The solubility of thorium from Th 3 UO 8 and ZrTh 3 UO 10 ceramics was studied to evaluate the solubility constants for the materials. Zirconium was added in order to investigate potential additional stabilization of the thorium matrix from ZrO 2 . Studies were performed from pH 4 to pH 9 under both 100 Argon and 10 CO 2 /90 Ar at 25°C in 0.1M NaClO 4 . Reaction kinetics and equilibrium concentrations were evaluated for each condition. Rate constants increased with pH and varied from 6×10 -4 hr -1 to 4×10 -2 hr -1 . The surface area normalized dissolution rate decreased with increasing pH, the highest being 5×10 -7 gm -2 d -1 at pH 4. The solubility product constants calculated from the equilibrium concentrations for the two ceramics were equivalent, with K {spTh₃UO₈ }= -48.30.4 and K {spZrTh₃UO₈ = -47.90.9. The data was used to calculate the Th solution phase concentration. The result was compared to the dissolution of UO 2 from pH 5-9 in 0.1M NaClO 4 under a 1 CO 2 atmosphere at 25°C. It was found that the U from the UO 2 had a higher solution phase concentration than Th at high pH and was highly dependent upon the solution E h of the evaluated conditions.

The migration of fissiogenic Tc into the environment can be predicted by studying the dissolution behavior of Re, a chemical analogue of Tc, avoiding the use of a radioactive element at high concentration. We developed a series of experimental studies of the solubility of Re oxides under various oxidation states (+VII, +IV, and +III), in oxidizing and anoxic media, so as to verify the validity of the available thermodynamic data concerning Re. The experimental results confirm that the predictable solubility of Re, under the conditions found in radioactive wastes storage, is very high when in the form of {ReO 4 - }, an analogue of {TcO 4 - }. The Re(III) oxide, Re 2 O 3 , is not stable in aqueous solutions and therefore the existence of Re(III) in surface conditions is not much likely. The Re(IV) oxide, ReO 2 , is weakly soluble. Its solubility is in the range 4×10 -7 -10 -6 mol L -1 , which suggests that Re(IV) can be found in noticeable concentrations in aqueous solutions even in anoxic media; similar result is expected for Tc.

The simultaneous permeation of Sc, Y, Ce, Pm, Eu, Gd, Yb and Lu through a 2-ethylhexyl phosphonic acid-2-ethylhexyl ester (EHEHPA)-decalin membrane supported on a microporous polytetrafluoroethylene sheet was studied using a multitracer. The permeation rates of the elements from feed solutions of various acidity into receiving solutions of 2mol dm -3 HCl were determined. The feed solution at pH 1.5 gave the highest percentage of permeation for Ce, Pm, Eu, Gd and Yb, amounting to about 90 after -25h permeation. The percentage of permeation of Y and Lu was the highest at pH 1, amounting to about 90 after -25h permeation. The permeation of Sc from all the feed solutions was less than 4 due to its adsorption on the vessel. The permeation from the feed solution at pH 1.5 into the receiving solutions of 1, 2, 3, 4 and 5mol dm -3 HCl showed that the maximum percentage of transport for Y and Yb was obtained in 2mol dm -3 HCl receiving solution and that for Lu in 2-4mol dm -3 HCl receiving solutions. The other elements gave a percentage of transport more than 90 in 1-5mol dm -3 HCl receiving solutions, showing no obvious HCl concentration effect. The permeability coefficients of these elements were determined. Solvent extraction of the elements by EHEHPA-decalin was also carried out for comparison.

The sorption behaviour of Ba 2+ in three different clay minerals from various regions of Turkey has been investigated by means of a tracer technique using 133 Ba in batch experiments. Sorption of Ba 2+ on montmorillonite, kaolinite and illite has been studied in mixed solutions of BaCl 2 and NaCl at ionic strengths ranging from 1×10 -3 M to 1×10 -1 M. The L-shape exchange isotherms for Ba 2+ -Na + systems are well defined by a Langmuir type equation. The exchange capacity of Ba 2+ ions for all three clay minerals increased with decreasing ionic strength. The adsorption data were fitted to a Freundlich isotherm and empirical Freundlich parameters enabled to the generation of a site distribution function. The selectivity coefficients were nearly constant at low Ba loading and decreased as loading increased. This behavior was an indication of an ion exchange process between Ba 2+ and Na + ions.

At the PWR Paks (Hungary) the diluted radioactive waste water is converted to a concentrate by evaporation and the concentrate is stored in tanks. The most important radionuclides in these solutions are 134 Cs, 137 Cs and 60 Co. In this research we studied granular potassium nickel hexacyanoferrate(II) as a Cs-selective ion-exchanger. Its capacity depended on the preparation method, temperature of pretreatment and age of the ion exchanger. We investigated also the effect of metal ions (Fe 2+ , Fe 3+ , Mn 2+ , Mg 2+ , Ca 2+ , Co 2+ , Ni 2+ , Cu 2+ ) on the Cs-capacity in the presence of complex forming compounds citrate, oxalate and EDTA. The cesium ion exchange capacity increased with addition of inactive cobalt or nickel salts. Additionally we studied filtration, adsorption and ultrafiltration separation processes for cobalt removal. The results showed that only adsorption by active carbon could be successfully used for the cobalt removal from evaporation concentrates. Experiments were performed both in the laboratory and at the PWR Paks.

Nickel reactions with gluconic acid (Gl) and α -isosaccharinic acid (ISA) have been investigated from pH 7 to pH 13.3. Measurement of the stoichiometries of the products of these reactions showed that NiGl and NiISA were formed at pH<7, Ni 2 Gl(OH) 3 and Ni 2 ISA(OH) 3 were formed at pH values between 7 and 10 and Ni 2 Gl(OH) 4 and Ni 2 ISA(OH) 4 were formed at pH>10. The stability constants for the formation of the soluble complexes were measured using an ion exchange resin method (Schubert method) at pH 7 and 13.3, and differential pulse polarography at pH 7. The polarographic measurements were performed in order to check the validity of the Schubert method at pH 7. This was due to the possibility of any cationic complexes that may have been formed sorbing to the resin. The importance of determining the stoichiometry of the reactions before calculating the stability constants from measurements taken using the Schubert method is emphasised.

The dopamine D 4 receptor (D 4 R) is expressed in low density in various extrastriatal brain regions. This receptor subtype is discussed in relation to the pathophysiology and treatment of schizophrenia but to date no selective positron emission tomography (PET) ligand is available to study its distribution in vivo . The 7-azaindole derivative 3-{[4-(4-iodophenyl)piperazin-1-yl]-methyl}-1 H -pyrrolo[2,3-b]pyridine (L-750,667) is a novel, high-affinity ( K i =0.51nM) and selective D 4 R ligand. L-750,667 analogue 3-{[4-(4-[ 18 F]fluorobenzyl)]piperazin-1-yl}methyl-1H-pyrrolo[2,3-b]-pyridine was prepared by reacting 3-(piperazin-1-yl)-methyl-1 H -pyrrolo[2,3-b]pyridine with 4-[ 18 F]fluorobenzaldehyde, which was labeled with no carrier added [ 18 F]fluoride. The radiochemical yield of 3-{[4-(4-[ 18 F]fluorobenzyl)]piperazin-1-yl}methyl-1 H -pyrrolo[2,3-b]pyridine was 12.0 at end of synthesis (EOS), and the synthesis time was 73min. The labeled benzaldehydes may be useful precursors for the radiosyntheses of other complex radiotracers for PET.