Band 101, Heft 10

Cross sections of 45 Sc( n, 2 n ) 44m,g Sc reactions and their isomeric cross section ratios σ m /σ g have been measured at three neutron energies between 13.5 and 14 . 8 MeV using the activation technique. The pure cross section of the groundstate was then obtained by utilizing the absolute cross section of the metastable state and analysis methods of residual nuclear decay. The monoenergetic neutron beam was produced via the 3 H( d, n ) 4 He reaction. The cross sections were also estimated with the TALYS-1.2 nuclear model code using different level density options, at neutron energies varying from the reaction threshold to 20 MeV. Results are also discussed and compared with some corresponding values found in the literature.

The spectrum of fast neutrons having energies from 0.5 to 20 MeV in the core of the 3MW TRIGA Mark II reactor at Savar, Dhaka, Bangladesh, was unfolded by activating several metal foils to induce threshold nuclear reactions covering the whole spectrum, and then doing necessary iterative calculations utilizing the activation results and the code SULSA. The analysed shape of the spectrum in the TRIGA core was found to be similar to that of the pure 235 U-fission spectrum, except for the energies between 0.5 and 1 . 5 MeV, where it was slightly higher than the fission spectrum. Spectrum-averaged cross sections were determined by integral measurements. The integral values measured in this work were compared with the recommended values for a pure fission spectrum as well as with the integrated data deduced from measured and evaluated excitation functions of a few reactions given in some data files. The good agreement between integral measurements and integrated data in case of well-investigated reactions shows that the fast neutron field at the TRIGA Mark II reactor can be used for validation of evaluated data of neutron threshold reactions.

This paper presents a simple and accurate method for determination of uranium isotopes ( 234 U and 238 U ) in seawater samples using alpha spectrometry. Uranium is pre-concentrated from seawater samples via adsorption on hydrotalcite at pH 6.5. The absorbent is dissolved into 50 ml of 8M HNO 3 ; then filtered through a Dowex-1 column. U(VI) in the elution solution is reduced to U(IV) using zinc metal in 4M solution of HCl and then co-precipitated with LaF 3 . The chemical separation efficiency is found to be 97 . 12±2 . 68%, eliminating the need of using 232 U tracer in other published methods. This method is validated via comparison with results obtained using inductively coupled plasma mass spectrometry (ICP-MS) and neutron activation analysis (NAA) for three seawater samples.

Trigonal sodium uranyl carbonate, Na 4 [UO 2 (CO 3 ) 3 ], has been synthesized under hydrothermal conditions, and its incorporation of IO 3 − , IO 4 − , SeO 3 2− , and SeO 4 2− has been investigated. LA-ICP-MS was used to detect the presence and concentration of iodine, selenium, and uranium in single crystals of Na 4 [UO 2 (CO 3 ) 3 ], and these in-situ analyses indicate that IO 3 − , IO 4 − , SeO 3 2− , and SeO 4 2− have been incorporated into its structure. The proposed mechanisms are the substitution of IO 3 − , IO 4 − , SeO 3 2− , and SeO 4 2− for CO 3 2− . The incorporation of iodine oxoanions results in the loss of Na+ cations so as to maintain charge balance; the substitution schemes may be expressed as follows:□+IO 3 − ↔Na + + CO 3 2− and □+IO 4 − ↔Na + +CO 3 2− (□ = vacancy).

The synthesis of uranyl complexes coordinated to tridentate, monoanionic salicylaldiminate (Schiff base) ligands was achieved by the reaction of UO 2 Cl 2 (THF) 3 , 1 , with one equivalent of the corresponding sodium salicylaldiminate salts affording [(C 9 H 6 N)N=C(H)C 6 H 2 t Bu 2 O]UO 2 Cl(THF), 2 , [(NC 5 H 4 )N=C(H)C 6 H 2 t Bu 2 O]UO 2 Cl(THF), 3 , and [(C 6 H 4 SCH 3 )N=C(H)C 6 H 2 t Bu 2 O]UO 2 Cl(THF), 4 . These are uncommon examples of uranyl complexes with a monoanionic ancillary ligand to stabilize the coordination sphere and one chloride ligand. Compounds 2 - 4 have been characterized by 1 H and 13 C NMR spectroscopy as well as IR and UVVis spectroscopy and their structures determined by X-ray crystallography.

Lead-gold eutectic (LGE) has been recently proposed as an alternative target material for high power spallation sources. In order to compare the corrosive properties of LGE to the better-studied eutectic of lead-bismuth (LBE), an isothermal twin-loop made of SS 316L was built and operated at the Institute of Physics of the University of Latvia. We have measured the concentration of steel alloying elements dissolved in both alloys at the end of two test campaigns via ICP-OES. In case of LGE, a pronounced concentration increase of Fe, Ni, Mn and Cr is found in the liquid metal, which is significantly higher compared to LBE. Similar results were obtained during complementary investigations on material samples exposed to both alloys in this twin-loop at 400 ◦C and 450 ◦C. These findings indicate that in contact with LGE, SS 316L steel suffers from substantial chemical attack. Detailed investigations using structure materials other than SS 316L have to be undertaken before qualifying LGE as a serious alternative to LBE.

The solubility and solid phase stability of zirconium hydroxide was investigated in the acidic pH range after heating the aqueous samples at 50, 70 and 90 ◦C. The solubility measured at room temperature after exposing the batch samples to elevated temperatures for a given period of time significantly decreased with increasing heating periods. The Zr concentrations at given pH after heating at 90 ◦C for 3 weeks are about 5 orders of magnitude lower than the solubility of amorphous zirconium hydroxide (Zr(OH) 4 (am)) kept at room temperature. Size distributions of the Zr colloidal species after heating were investigated by sequential filtration using different pore-sized membranes, and the contribution of the colloidal species to the solubility was assessed. The TEM images and XRD spectra of the solid phases after heating indicated the agglomeration and crystallization of the initial amorphous hydroxide solid phase. The solid phase was identified as crystalline oxide after heating at 90 ◦ C. The solubility product determined from the solubility data excluding contributions of colloidal species is correlated to the particle size of the solid phase.

A technique of selenium purification from 232 Th, 238 U, 226 , 228 Ra, 227 Ac and 40K was developed. This technique is simple to perform and employs a minimum number of highly pure reagents (bidistilled water, nitric acid). Operations carried out during purification (elution, evaporation) practically exclude losses of the target product (chemical yields of Se > 99%). A test purification of 100 g of selenium was carried out using this technique. The efficiency of this technique was confirmed by low background gamma spectrometry of the purified selenium sample. Distribution coefficients of Th, U, Ra and Ac on DOWEX 50W-×8 cation-exchange resin at different concentrations of selenium and nitric acid were experimentally determinated. Instrumental neutron activation analysis of bidistilled water, deionized water and nitric acid was performed.

The presented work aims at a radiochemical analysis of the radionuclide inventory of a solid lead target irradiated with high energetic protons in the spallation neutron facility SINQ at Paul Scherrer Institute. Lead samples from the vicinity of the beam entry have been extracted. A detailed γ -analysis shows the radial distribution of selected radionuclides relative to the incoming beam. The concentrations of these nuclides are evaluated in dependence on the proton beam profile.

89 Sr, a pure beta emitter with half life of 50 . 53 d is used as its chloride solution for palliative care of bone metastases. This paper describes the feasibility studies that have been conducted at FBTR, IGCAR for production of this radionuclide using the 89 Y( n, p ) 89 Sr reaction. Yttria pellets were irradiated in a special subassembly at the core centre for a total of 73 d in two steps of 35 d and 38 d with a time gap of 38 d. The irradiated yttria target was dissolved in nitric acid and the bulk Y was separated by solvent extraction using the TBP-HNO 3 complex. The 89Sr fraction was purified using the cation exchange resin DOWEX 50W×8 (100-200 mesh size) from the other radioactive impurities seen. The eluted 89 Sr fraction was assayed using a GM counting system. The 89 Sr activity produced in 1 g of yttria pellet was found to be 19 mCi.

Methods for the small scale synthesis of I-131 labelled iodine species relevant to severe nuclear accidents in light water reactors have been developed. The introduced methods allow the synthesis of impurity free, volatile, inorganic elemental iodine and volatile, organic iodides such as methyl- and ethyl iodide, as well as butyl iodide, chloroiodomethane, allyl iodide and benzyl iodide with ease. The radioactive iodine containing products are sufficiently stable to allow their storage for later use. Due to their volatility the liquid species can be easily converted into gaseous species and thus can be used in research in liquid and gaseous phase. The primary motivation for the development of these synthesis methods is to study the behaviour of volatile iodine species under the conditions of a severe nuclear accident in a light water reactor. Thus, the chemicals involved in the synthesis are chosen in a way to not generate impurities (chlorine and organic solvents) in the products which interfere with competing reactions relevant during a severe nuclear accident. Teknopox Aqua VA epoxy paint, which is used in Swedish light water reactor containments, and its reactions with the produced iodine species are described. The synthesised iodine species undergo chemisorption on paint films. Different to elemental iodine, the organic iodides are non-reactive with copper surfaces. The sorbed iodine species are partly re-released mainly in form of organic iodides and not as elemental iodine when the exposed paint films are heat treated. The partitioning and hydrolysis behaviour of gaseous methyl- and ethyl iodide between containment gas phase and water pools is found to be similar. The methods have been designed to minimise the use of harmful materials and the production of radioactive waste.