Band 101, Heft 4 -

Integral cross sections of the reactions 24 Mg( n , p ) 24 Na, 27 Al( n , p ) 27 Mg, 27 Al( n , α ) 24 Na and 95 Mo( n , p ) 95 Nb were measured for the first time with fast neutrons ( E n > 1.5 MeV) from an Am/Be source. Furthermore, upper cross section limits for the reactions 98 Mo( n , α ) 95 Zr and 103 Rh( n , p ) 103 Ru were deduced. The results were compared with data calculated using the neutron spectral distribution and the excitation function of each reaction given in the data files and libraries ENDF/B-VII, JEFF-3.1.2, JENDL-4.0, IRDF-2004, TENDL-2010, ROSFOND-2010 and CENDL-3.1. In general, the integral measurement and the integrated value agreed within ± 10%. The fast neutron field (with E n > 1.5 MeV) of the Am/Be source is thus well suited for integral tests of excitation functions of neutron threshold reactions.

Metallic catcher foils have been investigated on their thermal release capabilities for future superheavy element studies. These catcher materials shall serve as connection between production and chemical investigation of superheavy elements (SHE) at vacuum conditions. The diffusion constants and activation energies of diffusion have been extrapolated for various catcher materials using an atomic volume based model. Release rates can now be estimated for predefined experimental conditions using the determined diffusion values. The potential release behavior of the volatile SHE Cn (E112), E113, Fl (E114), E115, and Lv (E116) from polycrystalline, metallic foils of Ni, Y, Zr, Nb, Mo, Hf, Ta, and W is predicted. Example calculations showed that Zr is the best suited material in terms of on-line release efficiency and long-term operation stability. If higher temperatures up to 2773 K are applicable, tungsten is suggested to be the material of choice for such experiments.

The protonation constants of DTPA (diethylenetriaminepentaacetic acid) and two derivatives of DTPA, 1-R(4,4-diphenyl cyclohexyl-phosphonyl-methyl diethylenentriaminepentaacetic acid (MS-325) and (R)-hydroxymethyl-diethylenentriaminepentaacetic acid (HMDTPA) were determined by potentiometric titration in 0.1 M NaClO 4 . The formation of 1 : 1 complexes of Am 3+ , Cm 3+ and Ln 3+ cations with these three ligands were investigated by potentiometric titration with competition by ethylenediaminetetraacetic acid (EDTA) and the solvent extraction method in aqueous solutions of I =0.10 M NaClO 4 . The thermodynamic data of complexation were determined by the temperature dependence of the stability constants and by calorimetry. The complexation is exothermic and becomes weaker with increase in temperature. The complexation strength of these ligands follows the order: DTPA ≈ HMDTPA > MS-325. Eu 3+ /Cm 3+ luminescence, EXAFS (Extended X-ray Absorption Fine Structure) and DFT (Density Functional Theory) calculations suggest that all three ligands are octadentate in the complex. In the complex, M(L) 2− (L = DTPA, MS-325 and HMDTPA). The M 3+ binds via five carboxylates oxygen atoms, three nitrogen atoms, and the complex contains one water of hydration.

We describe the synthesis of cerium, thorium and uranium oxide nanoparticles embedded in a mesoporous matrix as template in a kind of nanocasting technique. The solid matrix is used as a template to obtain and stabilize the actinide oxide nanoparticles. We apply high resolution transmission electron microscopy (HR-TEM) to show evidence of metal oxide incorporation into the matrix pores and analyze their structure. Measured interplanar distances and calculated lattice parameters for synthesized nanosized CeO 2− x and ThO 2 samples differ from their bulk crystalline counterparts. We obtain with our synthesis CeO 2− x particles containing both Ce 4+ and larger sized Ce 3+ . The lattice parameter for these ceria nanoparticles is found to be larger than the bulk value due to the presence of Ce 3+ with its larger ionic radius. The presence of Ce 3+ was established by means of high resolution X-ray emission spectroscopy (HRXES), applied to the investigation of nanoparticles for the first time. The ThO 2 nanoparticles exhibit a decrease in interplanar distances, as one might generally expected for these nanoclusters. However, the lattice distance decrease for our particles is remarkable, up to 5%, indicating that contact with the surrounding silica matrix may exert a bond distance shortening effect such as through significant external pressure on the particle surface.

A radioanalytical method based on the use of a single TRU extraction chromatographic column and selective, on-column oxidation state adjustment of actinides was developed for the determination of Th, U, Np, Pu and Am(Cm) in environmental samples (such as sediment and swipe samples). The procedure of Vajda et al. [1] was further investigated and optimized focusing on the separation of Th, U and Np. The improved method combines two measurement techniques — alpha spectrometry and inductively coupled plasma mass spectrometry (ICP-MS) – which allows to obtain more reliable information on a wider range of isotopes: 228 Th, 230 Th, 232 Th, 234 U, 235 U, ( 236 U), 238 U, 237 Np, 238 Pu, 239 Pu, 240 Pu, 241 Pu, 241 Am, 242 Cm, 243 Cm and 244 Cm from one sample.

Gold nanoporous film (AuNPF) was grown on gold substrate by electrochemical oxidation of the gold electrode at 5 V for 180 s in phosphate buffer (pH 7.4) followed by reduction of the oxidized gold with ascorbic acid solution. Atomic force microscopy (AFM) showed the porous nature of the prepared film. In cyclic voltammetric (CV) studies, anodic shift of 141 mV in the cathodic peak potential for the reduction of UO 2 2+ in 0.5 M H 2 SO 4 was observed at the AuNPF electrode, showing evidence of its enhanced electrochemical activity as compared to that of the bare Au electrode. The charge transfer studies done using electrochemical impedance spectroscopy indicated similar rates of the heterogeneous electron-transfer kinetics at the bare Au and the AuNPF electrodes. The Cottrell plots obtained from the chronoamperometric experiments showed the Cottrell linearity at the bare Au electrode. In contrast, the Cottrell plot of the AuNPF electrode showed deviation from the linearity at longer times and this is characteristic of the thin-layer diffusion coupled with the electron transfer. Therefore, the observed anodic shift at the AuNPF electrode for the reduction of UO 2 2+ was attributed to the contribution from thin-layer diffusion within the gold nanoporous film.

The redox chemistry of neptunium in irradiated 4 M nitric acid was investigated using γ -ray irradiation and UV/Vis spectroscopic measurements. Irradiation caused changes in the abundances of Np(V) and Np(VI) regardless of the initial fractional components of these oxidation states. At low absorbed doses Np(V) was oxidized to Np(VI) in irradiated solution, due to its reaction with oxidizing, radiolytically-produced, free radicals. However, when sufficient radiolytically-produced nitrous acid accumulated, the reduction of Np(VI) to Np(V) occurred, even at this high nitric acid concentration. Neptunium(IV) was not produced. A kinetic model which incorporates the standard water radiolysis reactions, estimated radical yields for 4 M HNO 3 , and rate constants for neptunium reactions available from the literature was used to successfully reproduce the experimental results.

Time resolved laser fluorescence spectroscopy (TRLFS) and X-ray absorption fine structure (XAFS) are used as complimentary techniques to show that the hetero-valent incorporation of europium into apatite at temperatures relevant to environmental and biological processes occurs at grain boundaries and not the crystallographic calcium sites as previously presumed. For this study, we focus on mechanisms at the solid solution interface and therefore define this temperature regime as the range in which liquid water exists (0–100 ºC). Site-selective TRLFS show that the local Eu 3+ symmetry does not match the presumed crystallographic site of incorporation. This is confirmed by XAFS results that show a deviation from the local environment in apatite. The transition of this amorphous europium to acrystallographic calcium site upon heating is then explained by grain growth and followed through a transition species by TRLFS.

In order to devise methodology to study various environmental matrices 28 pairs of coarse and fine air particulate samples were collected in the vicinity of an automotive workshop located at Tasmasipabad on Chaklala Road, Rawalpindi. The samples were collected using a Gent sampler and polycarbonate filters during the period 7 to 27 April 2009. These samples were analyzed using instrumental neutron activation analysis (INAA) using the low power Pakistan Atomic Research Reactor-2 (PARR-2). Reference materials (RMs) IAEA-SL1 and IAEA-S7 were used for calibration and quality assurance (QA) purpose. The gravimetric data for these samples were found to exceed the PM 2.5 and PM 10 national limits. Up to 34 elements were measured using the INAA optimized procedure.