Volume 95, Issue 4

Excitation functions were measured for the 89 Y( d , x ) 90m,88,87m,87m+g Y, 89 Y( d , x ) 88,89 Zr and 89 Y( d , x ) 85 Sr reactions in the energy range 9–40 MeV by the stacked-foil activation technique in combination with high resolution HPGe γ-ray spectroscopy. The data above 27 MeV have been measured for the first time. Yield calculations revealed that in the deuteron-induced activation of yttrium the direct production of 88 Y is about two times lower than that of 88 Zr. The maximum cross section for the production of the PET isotope 89 Zr by the Y+ d process is higher than by Y+ p . The yields and decay characteristics of the 88 Y and 88 Zr nuclides are suitable for thin layer activation (TLA) analysis.

The solubility and redox reactions of Pu(IV) hydrous oxide were analyzed by comparing total Pu concentrations, oxidation state distributions and simultaneously measured redox potentials under air and under Ar containing only traces of oxygen. At pH>3 the aqueous Pu concentration is dominated by Pu(V) for both solubility studies under air and argon. Combining all information strongly indicates that PuO 2+ x (s,hyd), mixed valent (Pu V ) 2 x (Pu IV ) 1-2 x O 2+ x (s,hyd) or (PuO 2.5 ) 2 x (PuO 2 ) 1-2 x (s,hyd) with x = 0.003 (present study) and x = 0.05–0.06 (literature studies under air), is the solubility controlling solid phase. It can be formed by the oxidation of PuO 2 (s,hyd) with the oxygen in the system and by co-precipitation of Pu(V) and Pu(IV). The Pu 4+ concentration is given by the known solubility product of Pu(IV) hydrous oxide and the PuO 2 + concentration is described by the solubility product ( K sp = [PuO 2 + ][OH - ]) for the fraction of Pu(V) in PuO 2+ x (s,hyd): log K ° sp = −14.0±0.8 at zero ionic strength. Small Pu(IV) colloids/polymers present in neutral to alkaline solutions at a constant level of log[Pu(IV)] coll = −8.3±1.0 play an important role for the redox potentials in these systems. Similar Pu(V) concentrations and redox potentials were reached from oversaturation in initially Pu(VI) solutions.

The unsaturated phosphotungstate K 10 P 2 W 17 O 61 and silicotungstate K 8 SiW 11 O 39 are strong and selective complexants of An(IV) in aqueous solution. In presence of these complexants, the redox properties of actinides are changed drastically due to stabilization of the tetravalent actinides. Redox potentials of Fe(III)/Fe(II) and U(VI)/U(IV) pairs were measured in K 10 P 2 W 17 O 61 and K 8 SiW 11 O 39 , solutions with various HClO 4 concentration and absolute complexes stability constants of Fe(III) ions with phosphotungstate and silicotungstate ions were determined: logβ abs Fe(III) =17.4 ± 0.8 and 20.1 ± 0.8 respectively. The equilibrium constant of reaction between U(VI) and Fe(II) in 1 M HClO 4 was determined. The equilibrium constant, K eq , depends on excess of heteropolyanion, and is close to 10 4 in 1 M HClO 4 at [P 2 W 17 O 61 ] free ∼ 5 × 10 -4 M.

A study of americium, uranium and europium extraction by various dialkyl-diarylamides of 2,6-pyridine-dicarboxylic (dipicolinic) acid has shown that maximum extractability is achieved by using polar fluorine-substituted diluents. Generally, the diamide extractability is found to increase with the alkyl radical length. We have demonstrated the possibility to separate Am and Eu in solutions with a nitric acid concentration of 0.5–2 mol/l. The extractability of these diamides with respect to the three metals rises with the acid concentration increase to 6 mol/l.

The internal gelation process and a suitable broth formulation with an uranium concentration of 1.3 M was used to produce air-dried uranium trioxide dihydrate (UO 3 ·2H 2 O) and carbon microspheres with crush strengths greater than 600 g per microsphere. The addition of carbon lowered the slow-pour densities of the air-dried microspheres by a minimum of 9% if all other conditions were held constant. The crush strengths of the air-dried microspheres with and without carbon remained very good. These microspheres were not prone to leach when they were washed with ammonium hydroxide, and they did not have the tendency to crack during subsequent heat treatments. For the UO 3 ·2H 2 O microspheres with and without carbon, dehydration occurred at the same rate. The dehydration was accompanied by spontaneous reduction of the urania to UO 2.67 . In the same temperature range, hydrogen and carbon can be used to further reduce the urania to uranium dioxide. Therefore, the loss of carbon during calcination appears to be unavoidable. The current recommendation on calcinations is to use a temperature of 600 °C or higher to minimize the loss of carbon. Dense and strong uranium fuel kernels with carbon were produced in argon at 1680 °C.

An attempt is made to prepare and characterize the working standards of 238 Pu by mixing solutions of enriched isotopes of 238 Pu and 239 Pu, available indigenously. The working standards were characterized using the recently developed interfering element correction methodology in thermal ionization mass spectrometry (TIMS) and the data were compared with those obtained by conventionally used alpha spectrometry. The results obtained by alpha spectrometry on various synthetic mixtures agreed within 0.5 to 1% to those determined by TIMS. These studies show that by mixing accurately weighable amounts of highly enriched 238 Pu and 239 Pu isotopes, it is possible to prepare and characterize the certified reference materials (CRMs) for 238 Pu, which have eluded the nuclear community until recently. The commercial availability of these CRMs would allow the traceability of 238 Pu measurements in Pu using different radio-analytical techniques, provide a common platform to the measurements made on 238 Pu by various nuclear material accounting laboratories around the world, and would also permit the use of newly developed TIMS methodology, by various laboratories, with confidence.

Five nuts, namely almond, cashew nuts, peanuts, pine nuts and pistachio, commonly consumed in Pakistan, were analyzed for their inorganic element contents. Instrumental neutron activation analysis (INAA) methodology, using different irradiation, cooling and counting protocols, was adopted to determine Al, Br, Ca, Cl, Co, Cs, Eu, Fe, Hg, K, La, Mg, Mn, Mo, Na, Rb, Sc, Se, Sr and Zn. The investigated nuts were found to contain substantial amounts of Ca, Cl, Fe, Mg, K, Na and Zn. Dietary intake of the essential inorganic elements present in these nuts, as compared to the recommended dietary allowance, has also been calculated. This has further substantiated the nutrient role of nuts in the prevention of cardiovascular disease, as in addition to their established efficacy in improving the lipid profile, they are a rich source of cardioprotective trace elements such as magnesium, zinc, iron and calcium. Toxic elements were present in very low concentrations in nuts.