Volume 95, Issue 2

The relatively long-lived positron emitters 64 Cu ( t 1/2 = 12.7 h), 76 Br ( t 1/2 = 16.2 h) and 124 I ( t 1/2 = 4.18 d) are finding increasing applications in positron emission tomography (PET). For precise determination of their positron emission intensities, each radionuclide was prepared via a charged particle induced reaction in a “no-carrier-added” form and with high radionuclidic purity. It was then subjected to γ -ray and X-ray spectroscopy as well as to anticoincidence beta and γγ -coincidence counting. The positron emission intensities measured were: 64 Cu (17.8 ± 0.4)%, 76 Br (58.2 ± 1.9)% and 124 I (22.0 ± 0.5)%. The intensity of the weak 1346 keV γ -ray emitted in the decay of 64 Cu was determined as (0.54 ± 0.03)%. Some implications of the precisely determined nuclear data are discussed.

A novel production method for n.c.a. 64 Cu based on deuteron irradiation of 64 Zn is presented. The production takes place through the 64 Zn( d , 2 p ) 64 Cu reaction using a deuteron beam of 19.5 MeV energy on highly enriched 64 Zn disks. An average yield over three irradiations of 31 MBq/μA h (850 μCi/μA h) and saturation yield of 575 MBq/μA (15.5 mCi/μA) at the end of the beam (EOB) was measured by γ-ray spectrometry. Two of the three runs, of low irradiation charge, were used for radiochemistry. The copper isotopes were separated from other radionuclidic impurities by the combination of cation and anion exchange chromatography. An average radiochemical yield of 90% was estimated for the two runs performed in this study, and the specific activity as determined using flame atomic absorption spectrometry was about 4 MBq/μg, 2 hours after EOB. An extrapolation of the present results to production conditions (50 μA, 10 h) indicates approximately 8 GBq/μg (220 mCi/μg) of specific activity. The overall uncertainty in these values is estimated to 15%.

An improved sample preparation method for the determination of americium and plutonium in sediment and soil samples by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) and alpha-spectrometry is described. The developed procedure involves a selective CaF 2 co-precipitation for pre-concentration and matrix removal followed by a sequential extraction chromatographic separation. The average chemical recovery of sample preparation was between 81–94% for both americium and plutonium. The method development also focused on the elimination of possible interferences in mass spectrometric analysis caused by molecular ions ( e.g. 238 U 1 H + , 204 Pb 36 Ar + or 208 Pb 16 O 2 + ) employing the suitable matrix separation prior to ICP-SFMS analysis coupled with a desolvation sample introduction system. For 239 Pu, 240 Pu, 241 Pu and 241 Am limits of detection of 15, 9.2, 14 and 23 fg g -1 was achieved by ICP-SFMS, respectively. The applied sample preparation and measurement can be carried out within 6 h for one batch of samples. Results of certified reference materials (IAEA-384 and IAEA-385) analysed by the two different measurement techniques agreed well with the recommended or information values.

The hydrolysis of tetravalent plutonium in 0.5 M HCl/NaCl has been investigated by a combination of spectroscopy and redox potential measurements in the concentration range from 10 -5 to 4×10 -4 M and at pH c 0.3–2.1. Redox potentials were both measured and calculated from the plutonium oxidation state distributions using well-known equilibrium constants for the redox reactions of plutonium. The plutonium oxidation states in solution were quantified by spectroscopy. The p e values calculated from the plutonium redox couples Pu(V)/Pu(VI) and PuO 2 (am,hyd)/Pu(V) were found to be consistent with the measured p e values whereas those calculated from the Pu(III)/Pu(IV) couple were found to deviate, suggesting that the formation constants selected in recent reviews for the mononuclear hydroxide complexes of Pu(IV) are overestimated. Combining the redox potentials and the spectroscopically determined Pu(III) and Pu(IV) concentrations, the formation constants of the first, second, and third mononuclear hydroxide complexes Pu(OH) n 4- n at I =0.5 M and 23 ± 2 °C are calculated and corrected to zero ionic strength using the specific ion interaction theory (SIT): log β ° 11 = 14.0 ± 0.2, log β ° 12 = 26.8 ± 0.6, and log β ° 13 = 38.9 ± 0.9.

The extraction properties of calix[4]arenes, substituted by CH 2 P(O)Alk 2 -group on the upper rim were studied. Extraction of Am and Eu by solutions of these substituted calix[4]arenes in m -nitrobenzotrifluoride, dichloroethane, methylen chloride and p -xylene from nitric acid was performed. It was shown that extraction efficiency of calix[4]arenes from the diluted ( C ≤ 0.3 M) nitric acid decreases according to substituent type at phosphorus atom in the following order: butyl ≈ propyl > ethyl > methyl. Such behavior is not typical for corresponding monodentate compounds, so it was preliminary called Anomalous Alkyl Effect (AAE). In order to find out the reasons of this effect the influence of calixarene structure, changing of diluent and the distribution of extractant between water/nitric acid and organic phases were studied. We have stated that CIP-45 (with ethyl substituents at phosphorus atom) transfers into water and nitric acid ( C ≤ 0.3 M) from m -nitrobenzotrifluoride solution for more than 80%. CIP-45 also transfers from dichloroethane solution: about 100% transfers into water and less than 10% transfers into 0.01 M HNO 3 . This compound fully transfers from p -xylene even into 0.3 M HNO 3 solution. Less than 5% of CIP-67 (with propyl substituents at phosphorus atom) transfer from organic phase (in any of used diluent) into water/nitric acid. IR-spectroscopy investigations of CIP-45 aqueous solutions displayed that the main reason of the extraction efficiency decreasing of these substituted calix[4]arenes from the diluted nitric acid may be the formation of calixarene hydrate. This hydrate is soluble in water, but already in diluted HNO 3 it transforms into water insoluble solvate.

The complexation of U(VI) with Aldrich humic acid (HA) was studied at pH 7 under exclusion of CO 2 . Using two independent laser-induced spectroscopic methods, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses (fs-TRLFS), the formation of the ternary U(VI) mono hydroxo humate complex UO 2 (OH)HA(I) by reaction of UO 2 OH + with HA was studied. Assuming that all proton exchanging functional groups of the HA are able to contribute to the complex formation, a mean stability constant of 6.58 ± 0.24 was derived for UO 2 (OH)HA(I). Alternatively, the analytical data were evaluated based on the metal ion charge neutralization model resulting in a complexation constant of 6.95 ± 0.10 and a loading capacity of 0.76 ± 0.28. An overall complexation constant of log β 0.1M = 14.89 ± 0.54 was calculated for the total reaction of U(VI) with HA starting from the non-hydrolyzed UO 2 2+ ion. This value agrees very well with literature data. Taking into account the UO 2 (OH)HA(I) complex, the speciation of U(VI) in presence of HA was recalculated. It was found, that the formation of UO 2 (OH)HA(I) can significantly influence the U(VI) distribution in the environmentally relevant pH region. As a consequence, the mobility of U(VI) in natural aquifer systems could be enhanced.

The radioactive 131 I was used as a tracer to study the kinetics of iodide ion-isotopic exchange reactions. The experiment was performed to study the effect of temperature, concentration of ionic solution, and amount of ion exchange resin on kinetics of exchange reactions. It was observed that under different experimental conditions, the initial rate and the amount of iodide ions exchanged calculated for Indion N-IP Type-2 resin were higher than that for Indion-830 Type-1 resins. It is expected that the same technique can be employed to assess the efficiency of various ion exchangers under different operating conditions.

Diffusive transport of neptunium, plutonium, tritiated water (HTO), Cs + and I - in compacted sand-bentonite mixtures was studied by a through-diffusion method. Experiments for Np were performed in the presence of carbonate where Np is stable as Np IV (CO 3 ) 2 (OH) 2 2- and those for Pu in the presence of fulvic acid where the Pu is stable as fulvic complexes. These experiments were performed under Ar ( p O 2 < 10 -6 atm). Effective diffusivity ( D e ) values of (1.81 ± 0.03) × 10 -10 , (1.8 ± 0.8) × 10 -10 , (5.1 ± 0.8) × 10 -11 and (9.0 ± 4.1) × 10 -11 m 2 s -1 were obtained for HTO, Cs + , I - and Np(CO 3 ) 2 (OH) 2 2- , respectively. The ratio of the D e to the diffusivity in bulk of the water was around 0.1 for Np(CO 3 ) 2 (OH) 2 2- , HTO and Cs + , which is consistent with the pore diffusion model. Observed diffusive transport of Pu was much smaller than those of HTO, Cs + , I - and Np(CO 3 ) 2 (OH) 2 2- probably because Pu was present as colloidal forms and that confined pore space in the compacted sand-bentonite mixtures does not allow diffusive transport of colloidal plutonium.