Volume 92, Issue 2 -

Cross sections of the reactions 103 Rh( n , n ′) 103m Rh, 115 In( n , n ′) 115m In, 232 Th( n , f ), 47 Ti( n , p ) 47 Sc, 64 Zn( n , p ) 64 Cu, 58 Ni( n , p ) 58 Co, 54 Fe( n , p ) 54 Mn, 46 Ti( n , p ) 46 Sc, 27 Al( n , p ) 27 Mg, 56 Fe( n , p ) 56 Mn, 24 Mg( n , p ) 24 Na, 59 Co( n , α ) 56 Mn, 27 Al( n , α ) 24 Na and 48 Ti( n , p ) 48 Sc were measured with average neutron energies above effective threshold by using the activation method through usage of spectrum average technique in an irradiation system where there are three equivalent Am/Be sources, each of which has 592 GBq activity. The cross sections were determined with reference to the fast neutron fission cross section of 238 U. The measured values and published values are generally in agreement.

Experimentally determined ionic radii ( r i ) of heavy actinides decrease irregularly with increasing of atomic number. In order to understand sources of this irregularity ionic radii of heavy actinides were compared with the radii of the maximum charge density ( R max ) of the outermost orbital radii of these cations. From the linear dependence of ionic radii on 2 j +1 weighted R max of the 6 p 1/2 and 6 p 3/2 orbitals new values of r i equal to 91.5 pm and 90.3 pm for Fm 3+ and Md 3+ , respectively, were calculated.

Chemical shifts (ChSh) of nine emission lines of the uranium L -series in uranium oxides UO 2+ x ( x =0-1) with respect to UO 2 were studied by using a precise crystal-diffraction X-ray spectrometer. ChSh of Lα 1 , α 2 uranium and thorium lines in solid solutions y UO 2 ·(1- y )ThO 2 ( y =0:1) were measured with respect to UO 2 and ThO 2 , respectively. The changes in energy of spin-orbital splitting (SOS) — Δ δnl ± of inner nl -orbitals of the uranium atom were calculated from the data of ChSh of spin-doublet lines. For UO 2+ x oxides, a linear decrease in Δ δnl ± values with increasing degree of uranium oxidation was found. Sign inversion of Δ δnl ± for uranium levels was found on passing to solid solutions. No change in the SOS energy of inner thorium levels was detected. The values of Δ δnl ± were found to correlate with the experimental values of the effective magnetic moment of uranium in oxides. On the basis of the comparison of experimental Δ δnl ± values with Dirac–Hartree–Fock atomic calculations, it was concluded that the observed variations in Δ δnl ± values are due to the redistribution of electron and spin density between the 5 f 7/2 - and 5 f 5/2 -levels of the fine structure of the uranium atom without changes in atomic charge state. On the basis of the hypothesis of intraatomic relativistic U5 f 7/2 ↔U5 f 5/2 transition, a model of paramagnetic moment formation on the uranium atom in uranium dioxide was proposed.

The redox behaviours of neptunium(VI,V) ions in aqueous solutions containing nitric and formic acids in the presence of Pt/SiO 2 catalyst have been studied. It was shown that neptunium(VI), being quite stable in 0.1-2.0M HNO 3 and 0.1-1.5M HCOOH, is reduced effectively to neptunium(V) inthe presence of ∼1 wt. % Pt/SiO 2 . In the presence of 0.05-0.5M urea (anti-nitrous agent) the reduction of neptunium(VI) proceeds to neptunium(IV) through the stage of the neptunium(V) formation. The effects of the solid-to-liquid mass to volume ratio, the concentration of urea, the concentration of nitricacid, the concentration of formic acid and the temperature on the rates of the Np(VI) and Np(V) reductions in the presence of ∼1 wt. % Pt/SiO 2 were investigated. It was proposed that both reactions proceed through the stage of the HCOOH activated adsorption on Pt catalyst. Mechanisms of the Np(VI) and Np(V) catalytic reductions by formic acid were postulated.

The migration of 90 Sr, 237 Np, 238 Pu and 241 Am in unsaturated Chinese loess under artificial rainfall condition was investigated at the CIRP´s field test site. Quartz containing 90 Sr, 237 Np, 238 Pu and 241 Am was introduced into an experimental pit and the pit was backfilled. Artificial rainfall of 10-15 mm/d was applied to the experimental pit for 1078 days. HTO was used for obtaining the migration rate of moisture water in the pit. Vertical core soil samples were taken twice a year and cut into 0.5cm long section soil samples. The section soil samples were weighed and wind dried. Radioactivity of 237 Np and 241 Am in the section soil samples was measured with a low energy photon detector (HPGe); 90 Sr and 238 Pu were determined with a low background α & β detector after chemical separation. During the experiment, moisture water at different depths was taken on a daily basis and 3 H in the moisture water samples was determined with liquid scintillation technique. Experimental result indicates that the downward migration rate of moisture water was 2.27 cm/d and the retardation factors of 90 Sr, 237 Np, 238 Pu and 241 Am in the loess unsaturated zone were 9.9 × 10 2 , 3.2 × 10 3 , 3.2 × 10 3 and 4.5 × 10 3 , respectively. This result suggests that 90 Sr, 237 Np, 238 Pu and 241 Am could be effectively retarded by the loess unsaturated zone.

The extraction behaviour of Np(IV) by 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) in the presence of tri- n -octyl phosphine oxide (TOPO) was investigated from nitric acid medium. The speciation studies, carried out by the slope analysis method, yielded binary species of the type Np(PBI) 4 when only HPBI was used as the extractant and ternary species of the type Np(PBI) 4 ·TOPO when both HPBI and TOPO were used as the extractants. The two-phase extraction constant for the binary species (log k ex ) was calculated to be 10.11±0.03, while that for the ternary species was found to be 17.24±0.05. Thermodynamic parameters for the binary and ternary extraction systems were also determined. Both the binary and ternary extraction systems were found to be highly spontaneous processes with predominant enthalpy stabilization. The very high negative entropy factor suggested contribution of unfavourable steric factors.

Picrolonic acid (HPA) in methylisobutylketone (MIBK) has been used for the extraction studies of Eu(III) and Tm(III) from pH 2 buffer solution. The composition of the organic adduct responsible for the extraction of these metal ions has been determined by slope analysis method that came out to be M(PA) 3 (M= Eu(III), Tm(III)). The effect of various anions and cations on the extraction of these metal ions has also been studied. Among the anions, fluoride, oxalate, citrate and cyanide ions masked the extraction, whereas Fe(III) Cu(II), Ni(II) and Co(II) has reduced the extraction. The formation constant of the organic adduct has also been calculated and discussed.

Hydrous manganese oxide (HMO) was synthesized and its ability to sorb 60 Co 2+ from aqueous solution was studied under static conditions as a function of contact time, cobalt concentration (10 -2 -10 -7 M), temperature (303-333K) and pH of adsorptive solution (2.2-11.4). X-ray diffraction was used in characterization of synthesized HMO. Low concentration of 60 Co 2+ solution, high pH and high temperature were the most favorable conditions for the adsorption process. The results show that the removal process is complete in 40 minutes, obeys a first order rate law and can be described using the Freundlich adsorption model. The standard enthalpy of the system was Δ H 0 = 12.5 ± 0.2 kJ mol -1 and cobalt desorption indicates that the uptake process proceeds via cation exchange. The removal of cobalt ions by HMO appears to be endothermic and irreversible. The values of calculated Δ G 0 and Δ S 0 were -17.0 ± 3.0 kJ mol -1 and (9.8 ± 0.2) × 10 -2 kJ K -1 mol -1 respectively, this indicates spontaneity of the process and the degree of freedom of ions is increased by adsorption.

Instrumental neutron activation analysis (INAA) has been used to determine some trace, minor and major elements in some cosmetic samples. These samples have been randomly selected from the Egyptian market. Some of these cosmetics are imported from the world market and the others are manufactured in Egypt. Up to 25 elements have been quantitatively determined in selected cosmetic samples. These elements are: As, Br, Ba, Ce, Co, Cr, Cs, Eu, Fe, Hf, K, La, Lu, Na, Sb, Sc, Sm, Rb, Ta, Tb, Th, U, W, Yb and Zn. Two certified standard reference materials have been used to assure the accuracy and precision of the technique, which are IAEA-405 and SL-1. Two different γ -radioactivity counting systems have been used and compared. Some of the analyzed samples contain some elements, which according to the list of the European Union must not be present in cosmetics. Moreover, some of these elements are present in a very high concentration. Thus, some of the analyzed samples contain arsenic, antimony, chromium and cobalt with the following respectively concentration ranges, in ppm, 0.37-3.67, 0.14-5.36, 2.94-29768 (∼3) and 0.52-4.12.

Radiolysis of [ 11 C]iomazenil was investigated in an aqueous solution. Preparation of [ 11 C]iomazenil with [ 11 C]CH 3 I produced a good radiochemical yield, however, its radiochemical purity was always less than 90 without additives. This poor radiochemical purity was attributed to radiolysis of [ 11 C]iomazenil. The degradation of [ 11 C]iomazenil via radiolysis was markedly facilitated in the presence of HCOONa (strong selective hydroxyl radical and hydrogen atom scavenger). On the other hand, the radiolysis was suppressed effectively in the presence of NaNO 3 (selective hydrated electron scavenger), suggesting participation of hydrated electrons in the radiolysis of [ 11 C]iomazenil. LC/MS analysis of the degradation product suggested that the major degradation product by radiolysis had a molecular weight of 285 corresponding to the deiodinated compound. The present study showed that a decrease in the radiochemical purity of [ 11 C]iomazenil was attributed to the radiolysis via the deiodination reaction by hydrated electron.