Band 99, Heft 3 -

Some production aspects of the Auger electron emitter 193m Pt ( T 1/2 =4.33 d) through the 192 Os(α,ߙ3 n )-process were investigated. Relatively thick targets of 99.65% enriched 192 Os, prepared by pressing or electrolytic deposition, were irradiated with 40 MeV α-particles for 3 h at a nominal beam current of 1.6 μA. The radioplatinum formed was chemically separated with a yield of 90% and the expensive target material was recovered with a yield of 85%. The radioactivity of 193m Pt was determined by high resolution X-ray spectrometry. The radionuclidic purity of 193m Pt amounted to 99%, the level of 195m Pt and 191 Pt impurities being each 0.5%. The batch yield of 193m Pt achieved was about 10 MBq with a specific activity of 1 GBq/μg Pt. Both the batch yield and the specific activity could be appreciably increased through improved targetry. A comparison of the cyclotron and reactor production routes of 193m Pt shows that the ( n ,ߙγ) reaction leads to high production yields but the α-particle induced reaction results in a product of higher radionuclidic purity and four orders of magnitude higher specific activity of 193m Pt.

The surface-mediated reduction of Pu(VI) upon sorption onto hematite colloids is addressed in the paper that bring some new light on the mechanisms of interaction of Pu in high valence states with different Fe(III) oxides. We study the sorption of Pu taken at two different total concentrations around 10 −9 and 10 −14  M using 239 Pu and short-lived 237 Pu tracer. In order to conclude on the mechanisms of Pu sorption onto hematite, the kinetics of sorption of Pu(IV) and Pu(VI) at two concenrations is studied as well as its leching behavior. The rate limiting step in Pu(VI) sorption is its surface-mediated reduction. The experimental evidence of the polymerization of Pu(IV) on the surface taken at Pu total concentration of ∼10 −9  M is presented based on the kinetics of sorption and leaching behavior.

Determination of the 235 U/ 238 U atom ratio is required for various applications. Thermal ionization mass spectrometry (TIMS) is generally used for this purpose since the method gives most precise results. However, the method has limitations like elaborate sample preparation and high cost. Thus, an alternative methodology based on low energy photon spectrometry (LEPS) was developed and tested using routine samples. It involves the determination of gamma (γ) activity at gamma energies of 63.3, 92.8, 143.6, and 185.7 keV in isotopic standard solutions of uranium and different enriched uranium sample solutions. The method is fast as it does not involve chemical treatment as in TIMS. In this paper, a comparative evaluation of thermal ionization mass spectrometry and low energy photon spectrometry is reported for the determination of the 235 U/ 238 U atom ratio. The results obtained by the two systems compare well with each other within the statistical uncertainties of each system. Between the two, low energy photon spectrometry will be useful for rapid analysis of routine samples of enriched uranium.

This work describes chromatographic radionuclide generator systems for the production of actinides and natural decay series elements. The generator systems begin with alpha emitting parent radioisotopes with half-lives ( T 1/2 ) of greater than one year and produce alpha or beta emitting radioisotopes with half-lives of hours to days. Chromatographic systems were chosen to minimize radiolytic damage to chromatographic supports, preserve the parent activity for repeated use, provide high purity daughter radionuclide tracers, and to minimize or eliminate the need for evaporation of solutions of the parent or daughter nuclides. Useful secondary separations involving the daughters of the initial parent radionuclide are also described. Separation systems for 210 Bi, 210 Po, 211 Pb, 212 Pb, 223 Ra, 224 Ra, 225 Ra, 225 Ac, 227 Th, 228 Th, 231 Th, 234 Th, and 239 Np are outlined in detail.

Metal ion complexing properties of the ligand PDAM (1,10-phenanthroline-2,9-dicarboxamide) are reported in relation to its possible use as a functional group for solvent extractants in the separation of Am(III) from Ln(III) (lanthanide) ions. PDAM is only slightly water soluble, but variation of the intense π–π * transitions in the UV spectrum of 2×10 −5  M PDAM solutions as a function of pH or metal ion concentration allowed for the determination of the protonation constant (p K ) and log K 1 values with metal ions. The p K of PDAM is 0.6±0.1 in 1.0 M NaClO 4 , the lowest for any 1,10-phenanthroline (phen) derivative (in contrast, p K phen=5.1), which is attributed to the electron-withdrawing properties of the amide substituents of PDAM. The weak proton basicity of PDAM may be an important factor in its use as the functional group of a solvent extractant from acidic solutions. The formation constants are determined by UV-Visible spectroscopy for the Ln(III) ions from La(III) to Lu(III) (excluding Pm(III)), as well as for Y(III), Sc(III), Th(IV), and the UO 2 2+ cation in 0.1 M NaClO 4 at 25 °C. The log K 1 values for the Ln(III) ions show only small changes from La(III) to Lu(III) (both have log K 1 = 3.80). The amide O-donors (oxygen donors) of the amide groups of PDAM appear to cause considerable stabilization of the complexes of PDAM as compared to those of phen, consistent with the idea that the neutral O-donor is a strong Lewis base towards large metal ions such as the Ln(III) ions. A reviewer has pointed out that the amide groups would also stabilize the complexes of PDAM by virtue of the chelate effect, in that PDAM is tetradentate, while phen is only bidentate. The small change in complex stability for PDAM complexes in passing from La(III) to Lu(III) is rationalized in terms of the idea that neutral O-donors stabilize the complexes of the large La(III) ion more than the smaller Lu(III) ion, offsetting the greater affinity of Lu(III) than La(III) for N-donor ligands. The complexes of Th(IV), Sc(III), and the UO 2 2+ cation with PDAM have log K 1 values slightly higher than those of the Ln(III) cations, while Y(III) forms a slightly less stable complex. The best-fit size of metal ion for coordination with PDAM is analyzed using molecular mechanics calculations. A fluorescence study shows that the free ligand PDAM fluoresces very strongly, but that the Ln(III) cations quench the fluorescence of PDAM rather than produce a chelation enhanced fluorescence (CHEF) effect as Ln(III) ions do with other phen-based tetradentate ligands. Possible reasons for the lack of a CHEF effect with PDAM are discussed.

The extent of complexation between natural humic acid (HA) and uranium(VI) has been investigated at the Ruprechtov natural analogue site, Czech Republic. Natural HA was extracted from the clay sediments enriched by organic matter and then characterized for their elemental composition, UV/Vis and infrared spectroscopic properties, exchange capacity and protonation constants. Moreover, the reference sample HA-leonardite was selected and studied for comparison. Complexation between natural HA and U(VI) was studied using the cation exchange technique at pH 5–6. The experimental work was focused on study dependence of U(VI) complexation with HA: i) on the concentration of HA 1–40 mg/l, and ii) on the concentration of U(VI) 1×10 −5 –1×10 −7  M. The charge neutralization model (CNM) was used for evaluation of the experimental data, modified in a way, that the total charge was divided among the individual U(VI) species in solution under given conditions. The stability constant value was determined to be logβ=4.32±0.50, LC=50–60%, being independent on the HA concentration at U(VI) concentrations of 1×10 −4  M. On the other hand, a dependence on the stability constant for the different U(VI) concentrations was observed. At close to real conditions of the site (U(VI)=1×10 −7  M and m HA=5 mg/l) the stability constant logβ=6.16, LC=50.3–52.7%.

The third-phase formation in the DHDECMP-dodecane-HNO 3 system during the actinides extraction was investigated based on the densities of the phases formed and the acid uptake by the DHDECMP phase. The effects of various parameters like nature of acids, diluents, temperature of extraction, acid molarity, and concentration of DHDECMP on the Third-phase formation were studied. The third-phase formation was also explained on the basis of results of small-angle neutron scattering studies (SANS).

Samples of certified aluminum base alloys were analyzed by semi-absolute, standardless k 0 -instrumental neutron activation analysis ( k 0 -INAA) for compositional decoding. Irradiations were performed at two research reactors located at Pakistan Institute of Nuclear Science and Technology having nominal thermal neutron fluxes of 10 13 and 10 12  cm −2 s −1 . The experimentally optimized parameters for NAA suggest a maximum of three sets of irradiations for the quantification of 8 major and minor elements. Moreover, the same conditions provided quantitative results for 10 other elements as impurities, which were not reported by the supplier of the reference material. The same alloys were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) where all impurity elements, quantified by k 0 -INAA, were below the detection limits. A comparison of % relative deviation of the results obtained by k 0 -INAA and ICP-OES revealed that the former has better accuracy than ICP-OES, but k 0 -INAA has poor limits of detection for Mg, Si and Ti in aluminum base alloy.

The radionuclide-generator based access to radiopharmaceutical isotopes represents a valuable alternative to directly produced isotopes at particle accelerators or nuclear reactors. The 44 Ti based generator is of increasing interest for the delivery of PET-radiopharmaceutical isotopes used for imaging. The product of this generator 44 Sc represents with its 3.97 h half-life and 94.3% positron branching [1] a very promising candidate for labeling PET radiopharmaceuticals. The long half-life of 58.9±0.3 y [2] of the 44 Ti assures a constant and long lasting production of the daughter nuclide. Here we present a gas phase separation method of scandium from titanium via thermal release in vacuum. Titanium foils were irradiated with 40 Ar to produce scandium in multi-nucleon transfer reactions. Another production reaction used was the irradiation of titanium by neutrons from the SINQ neutron source at the Paul Scherrer Institute (PSI). The titanium metal foils containing 44m Sc and 46 Sc were heated up for time periods of 15 and 60 min to temperatures between 900 °C and 1500 °C in vacuum. Thus, release properties of scandium from titanium under these conditions were studied. The released scandium was collected on tantalum foils and could be rinsed of with concentrated nitric acid resulting in carrier free scandium nitrate solutions. From the experimental results optimum release conditions are suggested.