Volume 96, Issue 12

Excitation functions of the reactions nat Te ( p , xn ) 120g,121,123,124,125,126,128,13 I were measured from their respective thresholds up to 63 MeV via the stacked foil technique. Thin targets were prepared by a vacuum deposition method. Irradiations were performed using AVF 930 cyclotron at the National Institute of Radiological Sciences. The concord and conflict between our excitation studies and the available literature data are shown. The high values of our cross sections for 125 I in comparison to some literature data are discussed. Our cross sections measurements validated some of the literature data obtained using enriched target isotopes. The integral yields of iodine radionuclides were deduced from the measured excitation curves. The estimated yield of 124 I via the nat Te( p , xn ) process over the energy range E p = 57 → 53 MeV is 16.7 MBq/μA h. The level of the radionuclidic impurities 125 I and 126 I is, however, rather high, so that it is not meaningful to produce 124 I using nat Te as target material.

Extraction of Am(III) and Ln(III) from NaClO 4 medium has been investigated with di(2-ethylhexyl) dithiophosphoric acid, di(2-ethylhexyl) monothiophosphoric acid, di(2-ethylhexyl) monothiophosphinic acid, octylphenyl dithiophosphinic acid and 11 kinds of dialkyl dithiophosphinic acids (alkyl = hexyl, heptyl, octyl, nonyl, 2-ethylhexyl, 1-methylheptyl, phenyl, chlorophenyl, methylphenyl, 2,5-dimethylphenyl, and 3,5-dichloro-4-methylphenyl) in xylene. The effect of chemical structures of those extractants on separation capability has been studied. The relationship between the slope value of the lg D −pH and extraction conditions can be described as: lg S = a lg( C HA / C M S /4 )+ b . In the presence of macro amounts of Eu(ClO 4 ) 3 , the formula, lg SF Am/Eu = B −2lg( C HL − D Eu /( D Eu +1) C Eu ), can well describe the relationship between separation factor and the extraction condition. A high separation factor (SF Am/Eu =2500) is obtained by solvent extraction from 1 mol/L NaNO 3 solution with 0.5 mol/L di(2-ethylhexyl) dithiophosphinic acid in toluene.

Trace amounts of oxidic plutonium species were studied by thermochromatography in silica glass columns in comparison to oxidic species of Th, Pa, U, Np, and Am. Humid oxygen was used as reactive admixture to the carrier gas helium. The thermochromatographic behavior of plutonium provides evidence for the oxidation of Pu(IV) to Pu(VI) with humid oxygen. The gas chromatographic transport of U, Np, and Pu is governed by the surface reaction MO 2 (OH) 2(g) ↔MO 3(ads) +H 2 O (g) , with M=U, Np, and Pu in the hexavalent state and competitive reactions of the actinide oxides with silica to nonvolatile compounds or solid solutions. There is good agreement with earlier volatility studies and the reported oxidation of PuO 2 with water. The oxidation to PuO 4 as claimed by Domanov [1] could not be confirmed.

In the supercritical fluid extraction of uranium from acidic medium employing TBP as co-solvent, effects of various parameters on extraction efficiency were studied. Variation in pressure (80–300 atm), temperature (308–353 K), CO 2 flow rate (0.5–3 mL/min), co-solvent percentage (1–10%), molarity of nitric acid (0.5–10 M) were found to influence uranium extraction efficiency. The uranium extraction efficiency depends on distribution ratio and kinetics of transport of U-TBP complex into supercritical CO 2 . In the 150–300 atm pressure range, variation in extraction efficiency was similar to that of uranium distribution ratio under equilibrium conditions. Whereas below 150 atm, it closely followed supercritical CO 2 density variation which could be attributed to non-equilibrium behavior that eventually attained equilibrium. In the non-equilibrium region, increased supercritical CO 2 density with pressure favored enhancement in solubility as well as extraction kinetics of the U-TBP complex. Increase in temperature generally resulted in enhanced volatility of U-TBP complex and a decrease in supercritical CO 2 density which in turn affected the extraction efficiency. Up to 333 K temperature, extraction efficiency gradually increased due to enhancement in volatility of U-TBP complex which more than compensates for decrease in the supercritical CO 2 density. Beyond this temperature, the steep fall in the extraction efficiency is attributed to combined effect of saturation in volatility of the U-TBP complex and significant decrease in the density of supercritical CO 2 approaching the critical value at which supercritical CO 2 tends to form large clusters thereby resulting in steep decrease in its solvating power. Extraction efficiency was found to increase with nitric acid molarity up to 7 M and afterwards showed small decrease possibly due to competitive co-extraction of HNO 3 . Up to CO 2 flow rate of 1 mL/min increase in extraction efficiency was observed which attained saturation afterwards. Linear increase in extraction efficiency was observed with the amount of TBP. Extraction efficiency was found to increase linearly with logarithm of extraction time. Under optimised conditions (150 atm, 333 K, 1 mL/min CO 2 flowrate, 10% co-solvent, 7 M nitric acid and 30 min dynamic extraction time) extraction efficiency was found to be (98±2) was observed. 30 min dynamic extraction mode was found equivalent to 40 min static mode. Online complexation mode was more efficient than in situ mode.

The hydrolysis constants of Th(IV) were determined using the solvent extraction method in a NaClO 4 solution at I =0.1 and 25 °C. A trace amount of thorium below the solubility limit was used in order to avoid the formation of polynuclear species and colloids in the experiment. The values were compared with the literature data. Considering the effect of competitive hydrolysis reactions under weak acid conditions, the complexation constants of Th(IV) with a series of dicarboxylic acids containing different alkyl chain lengths were determined.

The sorption of Eu(III) and actinide ions in various oxidation states from nitric acid solutions by an extraction chromatography resin containing 1 wt. % of the Kläui ligand Cp * Co[P(O)(OR) 2 ] 3 − [Cp * =pentamethylcyclopentadienyl, R=–CH 2 CH 2 CH 3 ] on Amberlite ® XAD-7HP was examined. At 0.3 M HNO 3 and a metal-to-ligand ratio of 0.07, the relative affinity of the resin for the ions investigated followed the order: tetravalent»hexavalent>trivalent>pentavalent; however, the relative affinity for the trivalent and hexavalent ions can be reversed, depending on the extent of ligand loading and the nitric acid concentration. The sorption of the tetravalent ions was exceptionally strong in the entire range of nitric acid concentration examined (0.2 to 8 M HNO 3 ). The large difference in the affinity of the resin with the Kläui ligand for tetravalent actinides compared to hexavalent actinides is unusual for ligands with the P=O donor moiety. Resin samples loaded with various actinide ions were examined spectrophotometrically. No Np(V) and Pu(III) species were identified on the resin; rather, reduction–oxidation (REDOX) reactions occurred during equilibration, resulting in their complete conversion to M(IV) species bound by the Kläui ligand. Similarly, the sorption behavior of Pu(VI) and Np(VI) was complicated by their reduction to M(IV) upon sorption. The observed REDOX processes were apparently driven by the extremely high affinity of the Kläui ligand for the tetravalent ions. The acid–base properties of the methyl derivative of the Kläui ligand were investigated in aqueous solution, and its p K a was found to be highly dependent upon the solution ionic strength. The binding constants of this ligand with various actinide ions measured in a mixed methanol/carbon tetrachloride solvent exhibited qualitative agreement with the sorption selectivity trends.

During spent nuclear fuel reprocessing ruthenium is liable to form black ruthenium deposits on the stainless steel walls of process equipments. These deposits promote corrosion and can eventually obstruct the off-gas lines. The results of decontamination of 304L stainless steel test specimens covered with RuO(OH) 2 · x H 2 O deposits by permanganate ions in alkaline medium are described. The ruthenium deposits were dissolved by oxidation of RuO(OH) 2 to RuO 4 2− ions, while the permanganate ions were reduced to MnO 4 2− ions and then to manganese dioxide MnO 2 . The parameters affecting the kinetics of oxidative dissolution of these deposits were examined. The results indicate that the oxidative dissolution kinetics depends on the instantaneous surface area of the deposit, and that the dissolution rate increases with the concentrations of MnO 4 − and OH − ions.

The reduction of pertechnetate (TcO 4 − ) with freshly prepared amorphous iron sulfide was investigated. The amorphous iron sulfide (FeS) was shown to have an elemental composition of FeS 0.97 for all of the size fractions and a point of zero charge of pH pzc =7.4. Solubility studies of FeS in various buffers indicated that in the pH range 6.1–9.0, the concentrations of dissociated Fe 2+ and S 2− were negligible. The reductive immobilization of TcO 4 − with FeS was shown to be accelerated by increasing ionic strength and strongly pH dependent. At pH values below the pH pzc , the positively charged FeS surface reacted much faster with TcO 4 − and had higher immobilization yields relative to the negatively charged FeS surface at pH values above pH pzc . The TcO 4 − −FeS reaction is consistent with a surface mediated reaction through ligand exchange. The TcO 4 − −FeS reductive immobilization reaction product was characterized by X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), Fourier transform infrared spectroscopy (FT-IR), and energy dispersive X-ray spectroscopy (EDS) and found to be predominantly TcO 2 . Studies on the reductive capacity of the FeS and the long term stability of the TcO 4 − −FeS reaction product under both anaerobic and aerobic environments shows the potential utility of the in situ gaseous (hydrogen sulfide gas) immobilization technology in solidification of TcO 4 − by creating a FeS permeable reaction barrier in the vadose zone.

The trimethylsilyl-protected phosphinimines (9-anthracenyl)Ph 2 P=NSiMe 3 and (1-naphthyl)Ph 2 P=NSiMe 3 and the ion pairs [(9-anthracenyl)Ph 2 P=NH 2 + ][MO 4 − ] and [(1-naphthyl)Ph 2 P=NH 2 + ][MO 4 − ] with M=Re or Tc were synthesized and characterized by 1 H and 31 P NMR, UV-Vis and fluorescence spectroscopy, elemental analysis, and/or single crystal X-ray diffraction. Radiochemical studies performed using 99m Tc and 186 Re as the tracers for 99 Tc and Re found the selectivity of the phosphiniminium cations for pertechnetate in the presence of a variety of anions found in the environment to be excellent. The crystallographic data reported for the structures are as follows: [(9-anthracenyl)Ph 2 P=NH 2 + ][ReO 4 − ] (H 21 C 26 NO 4 PRe) 2 , monoclinic ( P 2 1 / n ), a =11.3047(5) Å, b =16.3983(8) Å, c =12.2469(6) Å, β=92.344(1)°, Z =4; [(9-anthracenyl)Ph 2 P=NH 2 + ][TcO 4 − ] (H 21 C 26 NO 4 PTc) 3 , monoclinic ( P 2 1 / n ), a =11.3619(4) Å, b =12.2203(3) Å, c =25.7794(13) Å, β =92.162(1)°, Z =4.

New diagnostic uses of 6-[ 18 F]fluoro-L-DOPA ([ 18 F]FDOPA) for endocrine cancers and for focal hyperinsulism of infancy have renewed interest in simple and reproducible methods to synthesize it in high quantity. Fluorodestannylation is a simple and regioselective means to produce [ 18 F]FDOPA. We have successfully used post-target produced [ 18 F]F 2 as a labeling agent in fluorodestannylation. We are able to produce in one synthesis enough [ 18 F]FDOPA for several human PET studies at Turku PET Centre. The average radiochemical yield in 50 syntheses was 6.4±1.7% (calculated from [ 18 F]F − ), with radiochemical purity >98% and mean specific radioactivity at the end of synthesis 3.7±0.9 GBq/μmol. With this method the amounts of the reagents used in the synthesis are considerably reduced in comparison to other electrophilic labeling approaches. Thus the manipulations during the synthesis and the purification of the product are simplified.

Dimethyl 2-(fluoromethyl)-6-methyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate 4a, a fluorinated nifedipine analog, has been shown to elicit significant calcium channel blocker activity using a guinea pig ileal longitudinal smooth muscle model. In order to perform biological studies for detection of L-type calcium channel distribution, we decided to prepare the [ 18 F]-labeled compound. The latter compound was prepared in no-carrier-added (n.c.a.) form from dimethyl 2-(bromomethyl)-6-methyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate 2 in one step at 80 °C in Kryptofix[222]/K[ 18 F]F and acetonitrile as a solvent in 15 min. Column chromatography afforded the radiochemically pure compound in 20 min. Radiochemical purity of the 18 F-nifedipine was determined by RTLC and HPLC (>98%) and specific activity of 21–48 GBq/μmol (EOB).

The method for determination of major and trace elements in iron oxide [hematite (Fe 2 O 3 )] and sulfide [pyrite (FeS 2 ) and chalcopyrite (CuFeS 2 )] minerals using the k 0 -method of neutron activation analysis in both forms: instrumental ( k 0 -INAA) and radiochemical ( k 0 -RNAA) was suggested. In order to avoid interferences from iron on the determination of elements present in trace levels, radiochemical separation was made. Determination of the investigated elements in the aqueous phase was performed by k 0 -RNAA after extraction of iron by isoamyl acetate (IAA) and diisopropyl ether (DIPE) from hydrochloric acid solution. The distribution of 35 elements in extraction systems (with intermediate/medium and long half-lived radionuclides) present in the studied minerals was investigated.

IAEA-CU-2006-06 (ancient Chinese ceramic) has been analyzed by k 0 -INAA and the results for 31 elements are reported. Measurement on Si was done via the ( n , p ) reaction. The results of 23 elements are within ±10% of the target values and for 2 elements data are reported as information values. The results produce lower relative deviation if compared with the mean reported concentration values submitted by the laboratories participating in the proficiency test. The analysis involves full peak efficiency calibration of the HPGe detector for all counting geometries and characterization of neutron flux at the irradiation channel by determining thermal to epithermal flux ratio and epithermal flux shape factor using Au and Zr flux monitors. The u -score is less than 1 for majority of the elements.