Band 97, Heft 2

The ground state thermal neutron cross section and the resonance integral for the 165 Ho( n , γ) 166 Ho reaction in thermal and 1/ E regions, respectively, of a thermal reactor neutron spectrum have been measured experimentally by activation technique. The reaction product, 166 Ho in the ground state, is gaining considerable importance as a therapeutic radionuclide and precisely measured data of the reaction are of significance from the fundamental point of view as well as for application. In this work, the spectrographically pure holmium oxide (Ho 2 O 3 ) powder samples were irradiated with and without cadmium covers at the IEA-R1 reactor (IPEN, São Paulo), Brazil. The deviation of the neutron spectrum shape from 1/ E law was measured by co-irradiating Co, Zn, Zr and Au activation detectors with thermal and epithermal neutrons followed by regression and iterative procedures. The magnitudes of the discrepancies that can occur in measurements made with the ideal 1/ E law considerations in the epithermal range were studied. The measured thermal neutron cross section at the Maxwellian averaged thermal energy of 0.0253 eV is 59.0±2.1 b and for the resonance integral 657±36 b. The results are measured with good precision and indicated a consistency trend to resolve the discrepant status of the literature data. The results are compared with the values in main libraries such as ENDF/B-VII, JEF-2.2 and JENDL-3.2, and with other measurements in the literature.

Excitation functions of proton induced nuclear reactions on nat Se leading to the formation of the radionuclides 82,80m,77,76,75 Br, 75,73 Se and 77,76,72,71 As were measured from their respective thresholds up to 62 MeV. The selenium targets were prepared by vacuum deposition onto thin Al-backings. For the cross section measurements the conventional stacked-foil technique was used. Irradiations were performed at the AVF 930 cyclotron of the National Institute of Radiological Sciences in Chiba, Japan. Our results were compared with the available data in the literature, and some of the literature data obtained using isotopically enriched targets were used to validate our data. The experimental data sets generally showed good agreement. Integral yields of 75 Br, 76 Br, 77 Br, 80m Br and 82 Br were derived from the measured cross section data. The yield of 80m Br is quite high but, due to associated radionuclidic impurities, it is not meaningful to produce 80m Br using nat Se as target material.

The 74 Se( 18 O, p 3 n ) 88g Nb excitation function was measured and a maximum cross section of 495±5 mb was observed at and 18 O energy of 74.0 MeV. Experimental cross sections were compared to theoretical calculations using the computer code ALICE-91 and the values were found to be in good agreement. The half-life of 88g Nb was determined to be around 14.56±0.11 min.

Anion-exchange chromatography of element 105, dubnium (Db), produced in the 248 Cm( 19 F, 5 n ) 262 Db reaction is investigated together with the homologues Nb and Ta, and the pseudo-homologue Pa in 13.9 M hydrofluoric acid (HF) solution. The distribution coefficient ( K d ) of Db on an anion-exchange resin is successfully determined by running cycles of 1702 chromatographic column separations. The result clearly indicates that the adsorption of Db on the resin is significantly different from that of the homologues and that the adsorption of anionic fluoro complexes of these elements decreases in the sequence of Ta≈ Nb>Db≥Pa.

Pu speciation is investigated by X-ray absorption fine structure (XAFS) at the Pu L 3 -edge in Gorleben (GoHy) groundwater for Pu added to the groundwater in three different oxidation states (III, IV, VI). The GoHy groundwater stems from an anaerobic aquifer rich in humic substances (HS) (GoHy-532 with ∼60−70 mg/L DOC) and has a neutral pH. Analysis of XANES spectra shows that the samples contain Pu(IV), regardless if Pu(III), Pu(IV) or Pu(VI) is added to the groundwater. The GoHy-532 sample with Pu(VI) added has some Pu(V) and in addition Pu(IV). EXAFS analysis shows Pu-O bond distances to be split into a short and a longer distance. The short Pu-O distance is from bound hydroxy ligands resulting from Pu hydrolysis and/or from bonding to HS phenol groups. A Pu-Pu distance is also found at 3.82−3.85 Å, indicative of hydrolysis and polymeric species formation. Pu(IV) species formed in GoHy-532 are compared to Pu(IV) complexed with fulvic acid (FA) isolated from GoHy-532 at pH c 1.0 and 1.8. Results indicate that the hydrolysis is less pronounced in the natural groundwater samples than in the Pu(IV)-fulvates prepared from a colloid containing Pu(IV) solution. We observe the Gorleben GoHy and FA apparently stabilize small Pu(IV) hydrolysis species and inhibits precipitation of polynuclear hydrolysis products.

The sorption behavior of neptunium(V) on gibbsite (γ-Al(OH) 3 ) was studied by batch experiments in the presence/absence of ambient CO 2 as a function of solid-to-liquid ratio, pH, ionic strength, and Np(V) concentration. The sorption of 8×10 −6  M Np(V) at ionic strength of 0.1 M NaClO 4 was proportional to the solid-to-liquid ratio of gibbsite with a K d value of ∼45±6 mL/g at pH 9.0. The sorption behavior of Np(V) on gibbsite was strongly affected by ambient CO 2 and pH in the pH range of 6.0–10.0. In the presence of CO 2 at ionic strengths of 0.01 and 0.1 M NaClO 4 , the maximum Np(V) uptake was at pH 8.5 for 8×10 −6 and 7×10 −12  M Np(V). In the absence of CO 2 at the same ionic strengths, the Np(V) uptake increased with increasing pH up to ∼95% at pH 10.0. The sorption edges of Np(V) shifted by approximately one unit toward higher pH while increasing the concentration from 7×10 −12 to 8×10 -−6  M Np(V) and the amount of Np(V) sorbed at pH 8.5 decreased by ca. 40% under ambient air conditions. Ionic strength had no effect on the sorption of Np(V) onto gibbsite whether CO 2 was present or not, indicating the formation of inner-sphere surface complexes between Np(V) and γ-Al(OH) 3 .

Various β -diketones viz. acetylacetone (AA), trifluoroacetylacetone (TFA), hexafluoroacetylacetone (HFA), thenoyltrifluoroacetylacetone (TTA) and heptafluorobutanoylpivaroylmethane (FOD) were evaluated as chelating agents for the supercritical fluid extraction of thorium from tissue paper matrix. In-situ chelation mode was found to be more effective than online chelation mode. A combination of tributyl phosphate (TBP) and β -diketones further enhanced the extraction efficiency. The extraction efficiency trend observed in all the cases was: TTA>FOD>HFA>TFA>AA. A correlation was observed between extraction efficiency and degree of fluorination in the side arms of β -diketones. This could be attributed to the fact that in supercritical CO 2 , higher fluorination results in higher percentage of enol content, greater dissociation into enolate ion and higher solubility and stability of β -diketones as well as of Th- β -diketone chelates. Highest extraction efficiency with TTA was probably due to the presence of aromatic thenoyl group. The spectra of the extracted Th-chelates displayed peaks in the visible region, which shifted towards UV region with increasing fluorination. In the Th-TTA chelate spectrum, red shift was observed.

Electrodeposition of silver on copper substrate was carried out using alkaline plating baths for production of Cadmium-109 via the nat Ag( p , n ) 109 Cd nuclear reaction. The target could withstand 15 MeV proton beam currents of up to 150 μA; the 109 Cd production yield was 1.88 μCi/μA h (0.069 MBq/μA h). Cadmium-109 was separated from silver and non-isotopic impurities by ion-exchange chromatography.

The soil samples of nine different sites in Islamabad were studied for their elemental composition. Instrumental neutron activation analysis and atomic absorption spectrometry were employed and 33 elements were determined. The acquired data were analyzed using descriptive statistics, principal component analysis, cluster analysis, pollution level index and enrichment factor. A perusal of results shows a distribution of elemental concentration in two major groups, one along the highway and the other in industrial area of Islamabad. The soil along the highway sites was found to be relatively less polluted than at the sites in the industrial area. The enrichment factor indicates the presence of As, Pb, Sb, Se and Sn at higher levels. The method validation was done by analyzing IAEA reference materials SL-1 (lake sediment) and S7 (soil).