Volume 97, Issue 10

The radionuclides 75 Br and 76 Br are of considerable interest for application in Positron Emission Tomography (PET). For their production so far mostly low-energy or low-yield production processes have been employed. In this work the production of both isotopes was investigated using intermediate energy proton induced reactions and enriched target materials. Cross section data of the 77,78,80 Se( p , xn ) 75 Br processes were measured up to 66 MeV and those of the 77,78,80 Se( p , xn ) 76 Br processes up to 85 MeV. The measured excitation functions were compared with calculated results of the nuclear model code ALICE-IPPE. From the experimental excitation curves, thick target yields were calculated. They are fairly high over the investigated intermediate energy ranges. The production possibilities of 75 Br and 76 Br via various routes and the radionuclidic impurities associated with them are discussed.

The production of 48 V in a nuclear reactor, induced on titanium by tritons generated from the 6 Li( n , t ) 4 He reaction, and eventually 7 Li( n , n ′ t ) 4 He, is described. Samples of lithium titanate were irradiated for an irradiation cycle (120 h) in the RA-3 reactor, belonging to Ezeiza Atomic Centre. After a radiochemical separation, the characteristic radiations from 48 V were identified in the gamma ray spectra of the vanadium fractions.

Safety assessment of nuclear waste disposal includes determination of the possible impact of natural dissolved organic matter on the transport of actinide ions via groundwater into the biosphere. Thereby, much attention is paid to americium as it dominates the radiotoxicity of the nuclear waste after about 300 y and up to about 1000 y (spent fuel) or 100000 y (vitrified reprocessing waste). A trustworthy description of the influence benefits from a sound chemical process understanding of the americium humate complexation and transport processes. A problem in this respect is that studies by TRLFS lead to inconclusive results with respect to the nature of the complexes involved. In the present study the outcome of TRLFS measurements in H 2 O and D 2 O, and at room temperature and in liquid nitrogen are compared. It is shown that the Cm 3+ ion interchanges between aquo ion (Cm 3 aq ) and humate complex (CmHA) on a time scale of milliseconds in a pH range between 3 and 5.5. Taking this interchange into account, the process can be described in the absence of ternary complexes by the 1:1 stoichiometry formation of one curium humate complex, or a sufficiently narrow distribution of complexes to be represented by one average complex.

The paper reports the possibility of joint separation of 137 Cs and 85 Sr from neutral and alkaline aqueous solutions by their coprecipitation with the solid phase of complex compounds [M(18-crown-6)]BPh 4 (M=Na + , Cs + ), as well as to study the coprecipitation of 137 Cs and 85 Sr with the solid phase CsBPh 4 . It is found that complex compounds [M(18-crown-6)]BPh 4 (M=Na + , Cs + ) increased the degree of 85 Sr separation from solutions virtually two- to threefold vs. CsBPh 4 . Chloride and nitrate were found to have hardly any impact on the coprecipitation of 137 Cs and 85 Sr with [M(18-crown-6)]BPh 4 (M=Na + , Cs + ).

Solvent extraction and flat sheet liquid membrane (FSSLM) transport studies for radiostrontium separation from nitric acid medium were carried out using 4,4′(5′)-di- tert -butyl-dicyclohexano-18-crown-6 (DTBCH18C6) as the extractant. Role of diluent on the extraction and transport of Sr(II) was investigated. Encouraging results were obtained during the solvent extraction investigations using 0.1 M DTBCH18C6 in a diluent mixture comprising 80% toluene-20% 1-octanol as the solvent which displayed significantly lower nitric acid extraction as compared to pure 1-octanol as the diluent. However, a saturation transport value for Sr(II) was reported at about 60% which was primarily linked to acid transport. The influence of the composition of feed and receiver phase on the transport efficiency was also investigated.

The oxidation of UC powder was studied in 0.5–6.0 M HNO 3 and HClO 4 , containing 0.01–0.1 M NaNO 2 , at ambient temperature. The addition of nitrous acid caused the oxidation potential to exceed 400 mV/SCE and thus accelerated the dissolution and increased the dissolution yield to exceed 95%. One hundred percent dissolution at room temperature was achieved within 30 to 40 min when 3.0–6.0 M HNO 3 was used that contained more than 0.005 M HNO 2 .The dissolution rate increased with increasing HNO 3 concentration and initial solid-to-liquid ratio. The effective dissolution rate constants and reaction orders were estimated for the UC oxidation with H + , NO 3 - and HNO 2 in 0.5–6.0 M HClO 4 . The rate of UC oxidation with HNO 2 exceeded 50–80 times its oxidation rates with NO 3 - ions. During UC oxidation with HNO 2 in 0.5–6.0 M HClO 4 , 60–85% carbon was oxidized to CO 2 . The C/U(VI) ratio in the dissolver solution decreased from 0.5 to 0.1 mg eq/mol with increasing of HClO 4 and HNO 2 solution concentration. Two to five percent of the carbon remained in the insoluble residue of the HNO 3 dissolver solutions, even when a 100% U(VI) yield was observed. Scanning electron microscopy of the insoluble residue showed the carbon particle size between 1.0 and 5.0 μm.

The diffusivities of the key radionuclides in host rock are important for the performance assessment of repositories. One of the conventional methods for determining the diffusivities of radionuclides is to grind the rock tablet layer by layer and then to measure the radioactivity remaining on the rock tablet before each grinding cycle. Since grinding hard rock samples, especially those with radioactivity, is very difficult, we developed a new approach to determine the diffusivity of americium in granite. The new approach mainly includes two parts: one is to measure the radioactivities from both sides of a rock disk sample by autoradiography with phosphor imaging technique; the other is to study the relationship between the radioactivities and the apparent diffusivity of americium in granite by computer modelling. Because the high contamination risk of grinding radioactive rock samples has been avoided, the new approach is much simpler than the conventional method. It may be a better choice of measuring the diffusivities of radionuclides in rock, especially for those laboratories in which grinding radioactive rock samples is inconvenient.

Single crystals were prepared, and the structures of two complexes of Np(V) glycolate with 2,2′-bipyridine of the compositions [NpO 2 (C 10 H 8 N 2 )(OOC 2 H 2 OH)]·1.5H 2 O ( I ) and [NpO 2 (C 10 H 8 N 2 )(OOC 2 H 2 OH)]·2.5H 2 O ( II ) were studied. The structures of the compounds are based on neptunyl–glycolate chains in which the glycolate anion manifests its complexation ability in different manner. In structure I , the bidentate-bridging anion links the adjacent NpO 2 + cations through the oxygen atoms of the carboxylate group. The neptunyl–glycolate chains of I exhibits the mutual coordination of the NpO 2 + cations acting toward each other simultaneously as ligands and coordinating centers. In compound II , the glycolate anion is bidentately coordinated to one neptunium atom to form a planar five-membered metallocycle [NpOCCO]. The O atom external with respect to the metallocycle is in the coordination environment of the adjacent neptunyl. The nitrogen-containing molecular ligand Bipy is included into the coordination environment of Np. The coordination polyhedron of the Np atoms in both structures is a pentagonal bipyramid in which the average Np–N bond length is 2.666 Å ( I ) and 2.596 Å ( II ).

Americium (Am) and europium (Eu) extraction from HNO 3 and HClO 4 media by a synergistic mixture of 2,6-bis(1-aryl-1H-tetrazol-5-yl)pyridines (ATP) with chlorinated cobalt dicarbollide (CCD) was studied by using m -nitrobenzotrifluoride, phenyltrifluoromethyl sulfone, and 1,2-dichloroethane as diluents. We examined the effects of diluents, of the aqueous phase composition and the nature of substituents in the ATP aryl ring on Am/Eu extraction efficiency and selectivity. The Am/Eu separation factor was found to be close to 100 at the optimal ratio of ATPs:CCD∼1:1. We also studied the extraction of 85 Sr, 137 Cs and 133 Ba; a PhATP-CCD mixture provided the separation of the Sr/Ba pair with a factor of 35. A high resistance of 2,6-bis-aryltetrazolyl pyridines to 6 M nitric and perchloric acids at 95 °C was demonstrated.