The fast transfer system was modified to enable a fixed counting geometry with high reproductibility using an endcap geometry. The optimal count rate for short time activation analysis by means of the loss free counting system was found to be within 100–140 kcts/s, if a high accuracy is needed (1%). The method of calculating the peak area after the dead time and pile up corrections was modified by changing the peak fitting parameters gradually with increasing count rates. Epithermal activation by a6LiD converter was found to be an ideal irradiation technique for short time activation analysis especially for heavy elements due to the lower contribution of24Na and28Al (up to 30 fold).
Different pattern recognition techniques were applied for classification and characterization of a large number of coal, and coal fly ash samples. Cluster analysis was performed on 116 samples using the concentration data of 40 elements. The effect of the number and type of the elements on the clustering was studied in detail. It was proved that short time activation analysis enables the characterization of these types of samples if139Ba and87Sr are included, these data being obtained by increasing the irradiation and counting times. The two elements and chlorine were found to be necessary for such a classification. The combination between cluster analyses and principal component analysis gives accurate and confirmed results. The statistical analyses of the subgroups are compared.
Airborne samples representing dustfall, street, and household dusts of Aswan were collected; and ten elements (Si, Ti, Fe, Mn, K, Al, Ca, Mg, Na, and P) were chemically analysed by means of instrumental activation analysis (INAA), inductively coupled plasma (ICP), and X-ray fluorescence (XRF). The puzziling differences in the values of the enrichment factors (EF) and obvious contradiction with the mineralogy of the dustfall samples both indicate that this method of calculation could help to establish models of dust matrices in different geological and industrial regions rather than considering it only as a tool for assessing the source rocks.
A new counting geometry with a simple sample changer was constructed to enable cyclic and pseudocyclic short-time activation
analysis. With the new system it is possible to cycle a sample, or successively an indefinite number of samples up to 20 times.
The sample changer acts at the same time as sample catcher for two n-type HPGe detectors and can release the sample into a
well-type HPGe detector. The new system enables the simultaneous counting of the irradiated samples by means of two endcap
HPGe detectors, and subsequent counting by means of the well HPGe detector or both detector types. A well detector ensures
a high counting efficiency which improves the sensitivity of a large number of short lived nuclides. Some standard reference
materials (i.e., BCR-176, NIST SRM 1633b, IAEA-336, 335b, 335c) were prepared and analysed in replicates. The results indicate
that up to 46 nuclides can be determined in BCR-176 if the samples are irradiated with and without the6LiD converter. An automatic evaluation programme was developed that determines the FWHM calibration parameters for each spectrum
for accurate peak-area estimation at high count rates.
Various mushroom species have been analyzed for their elemental composition (i.e., Al, B, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, P, Sr and Zn) by means of ICP-AES. The accuracy of the measurements was confirmed by analyzing a series of the same samples by short time activation analysis. The data were evaluated statistically including the values of137Cs. The results denote that the distribution of these elements and their correlation of these elements and their correlation coefficients are highly distinctive for each mushroom species. K, Na and P were found to correlate negatively with137Cs in most species. Suillus grevillei and Cantharellus cibarius show high Be values (0.27 and 0.30 g g–1, respectively), while Pb was high in Suillus grevillei (16.3 g g–1) and Amanita rubescens (9.3 g g–1). Higher levels of Cd were found in Rozites caperata and Russula vesca with a mean of 9.2 and 16.1 g g–1, respectively. Cluster analysis was applied to classify these samples according to their botanical species using their elemental composition. The concentrations of Al, Cr, Mn, Na and137Cs have no influence on the classification of these samples.
The concentration of 18 elements in different cane sugar products, i.e., cane sugar plants, crude and syrup juices, molasses, and the end products of the consumer sugar, were analyzed and processed. The samples were collected from five citics, i.e., Kom Ombo, Edfu, Armant, Deshna and Naga Hammady in Upper Egypt where the main Egyptian sugar industry factories are located. INAA was applied for the determination of Al, Ca, Cl, Co, Cr, Fe, Mg, Mn, Na and Sc, while Cu, Li, P, Sn, V and Zn were determined by ICP-AES and Pb and As were determined by AAS. These three analytical methods were applied to optimize the sensitivity and the accuracy of the measurements in order to provide a sound basis for the obtention of reliable clustering results.
Sediment samples of the High Dam lake were investigated for their137Cs,226Ra,228Th, and40K content, using low-level -spectroscopy. The results show that at the begining of the lake (500 km from the High Dam), where sediments consist mostly of sand, the level of137Cs is very low (0.1 Bq kg–1). The maximum value (22.3 Bq kg–1) was found 40 km from the wall of the High Dam, where the composition of the sediments is nearly 50% clays. The distribution of the natural nuclides226Ra,228Th, and40K shows a different trend.
Copper and nickel oxide samples supported on MgO were prepared by wet impregnation method. The obtained solids were heated
at 350 °C and 450 °C. The extent of copper and nickel oxides was fixed at 16.7 mol%. The effect of g-irradiation (0.2-1.6
MGy) on the surface and catalytic properties of the solids were investigated. The techniques employed were XRD, nitrogen adsorption
at -196 °C and H2O2 decomposition. The results revealed that the g-irradiation up to 0.8 MGy of CuO/MgO-450 °C effected a measurable decrease
in the crystallite size of CuO phase with subsequent increase in its degree of ordering. Irradiation at a dose of 1.6 MGy
brought about a complete conversion of MgO into Mg(OH)2 during its cooling from 450 °C to room temperature via interacting with atmospheric water vapor. The SBET and total pore volume of CuO/MgO precalcined at 350 °C and 450 °C increased progressively as a function of g-ray dose reached
a maximum limit at 0.8 MGy. Gamma-irradiation of NiO/MgO-450 °C solids up to 0.8 MGy increased the degree of ordering of MgO
and NiO phases without changing their crystallite size. The exposure of these solids to 1.6 MGy led to an effective transformation
of some of NiO (not dissolved in MgO lattice) into Ni(OH)2 via interacting with atmospheric water vapor during cooling from 450 °C to room temperature. Gamma-irradiation led to a measurable
increase in the SBET and Vp of NiO/MgO system. Gamma-irradiation of the two investigated systems resulted in both increase and decrease in their catalytic
activities in H2O2 decomposition depending mainly on the irradiation dose and calcination temperature. This treatment, however, did not modify
the mechanism of the catalytic reaction, but changed the catalytic active sites without changing their energetic nature.
Authors:S. Ismail, A. Ghods, R. Awadallah, and F. Grass
A study was undertaken to determine element concentrations in Aswan High Dam Lake sediments. Sediment samples were collected from 40 to 500 km upstream of the dam to follow the sedimentation process and the distribution of Th, U and the trace elements in the lake. INAA was applied for the determination of Sm, Ce, Lu, Th, Cr, Yb, Au, Hf, Ba, Nd, Cs, Tb, Sc, Rb, Fe, Zn, Co, Eu, and Sb, while Laser Fluorimetry was applied for U determination. The accuracy and the reproducibility of the techniques were tested with IAEA standard materials (SL, Soil-7). The U values ranged from 4 ppm to 18 ppm, Th values were between 2 and 10 ppm, and showed a very good correlation with the rare earth elements and Fe. The distribution of most of the elements in the lake follows the same trend as the distribution of the clays in the sediments. Ba showed a negative correlation with most of the elements under investigation.
Authors:S. Ismail, G. Wiesinger, R. Pavlovec, and F. Grass
Different reference materials of environmental and geological origin, such as NBS 1633a (Coal Fly Ash, CFA), NBS 1645 (River Sediment, RS), GXR-2, and IAEA Soil-5, were investigated by short time activation analysis. The samples were analyzed in 5 replicates each between 100 to 150 mg, at neutron flux of 1.3 E 12 cm–2 s–1, using a high rate — high resolution gamma spectroscopy with a Loss Free Counting (LFC) System to correct the dead time and pile up to 500,000 cps. The results of the measurements indicate that the precision in determination of28Al,46mSc, and52V is between 1 to 6%. Different evaluation programs (i.e. ALCHEM, AKTAN, and ND-PEAK) were used to calculate the peak areas. The results indicate that, at lower counts, the statistical error of peak area calculation becomes more significant. Finally, Mössbauer spectroscopy was used to investigate the main Fe compounds present in some reference materials.