G. Kennedy

A γ-ray detection system for 3-D particle tracking in multiphase reactors

A system employing eight NaI detectors has been developed for tracking particles moving in a three-phase fluidized bed reactor. One particle is tagged with typically 2 MBq of 46Sc which emits high energy γ-rays. The system is calibrated by measuring the count-rates in the 8 detectors with the tagged particle placed at a number of locations in the reactor and then calculating the count-rates, using the Monte Carlo technique, at 19 200 locations. In a tracking experiment, data are accumulated in the multiscaling mode and the coordinates of the moving particle are calculatedby least-squares using the calibration map. With 30 ms counting intervals, the location of the particle is determined with a typical precision of 5 mm. The use of these data for determining velocity flow fields in multiphase reactors is illustrated.

Use of the semi-absolute method in neutron activation analysis

A new standardization method has been developed for neutron activation analysis. In this method, experimental activation constants, are determined for a given reactor power level and irradiation and counting position. The unusual feature of this technique is the fact that no flux monitor or standards are needed due to the exceptional stability of the reactor used. The semi-absolute method was tested over a three month period and its reliability was demonstrated for 6 elements of different neutrons cross-section characteristics.

Alzheimer type II astrocytic changes following sub-acute exposure to manganese and its prevention by antioxidant treatment

Exposure to manganese in an industrial or clinical setting can lead to manganism, a neurological disorder with similarities to Parkinsons disease. Although the pathogenetic basis of this disorder is unclear, studies indicate this metal is highly accumulated in astrocytes, suggesting an involvement of these glial cells. To investigate this issue, we have used a recently characterized, sub-acute model of manganese neurotoxicity. Treatment of rats with manganese (II) chloride (50 mg/kg body weight, i.p.) once daily for 1 or 4 days led to increases in manganese levels of up to 232, 523, and 427% in the cerebral cortex, globus pallidus, and cerebellum, respectively, by instrumental neutron activation analysis. These changes were accompanied by development of pathological changes in glial morphology identified as Alzheimer type II astrocytosis in both cortical and sub-cortical structures. Co-treatment with either the antioxidant N-acetylcysteine or the manganese chelator 1,2-cyclohexylenedinitrilotetraacetic acid completely blocked this pathology, indicating the cellular transformation may be mediated by oxidative stress associated with the presence of this metal. These findings represent, to our knowledge, the first report of early induction of this pathological hallmark of manganese neurotoxicity, an event previously considered a consequence of chronic exposure to manganese in primates and in human cases of manganism. Our results also indicate that use of this rodent model may provide a novel opportunity to examine the nature and role of the Alzheimer type II astrocyte in the pathophysiology of this disorder as well as in other disease processes in which cerebral accumulation of manganese occurs.

The pigeon (Columbia livia) as a monitor for manganese contamination from motor vehicles

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic derivative of manganese (Mn) used in unleaded gasoline in Canada since 1977. It has been suggested that the production of Mn3O4 resulting from the combustion of MMT may become one of the principal sources of manganese contamination in the urban environment. This research evaluates the feral pigeon (Columba livia) as a monitor of Mn contamination in rural (Lachute) and urban (Montreal) environments. Atmospheric Mn concentrations were measured over a 6-month period in the rural and urban areas. Twenty pigeons were captured in each area and the Mn concentrations of several tissues (liver, kidney, lung, pancreas, intestine, brain, down feathers, feces, whole blood, and blood serum) were measured by neutron activation. Biochemical profiles of the blood samples (total protein, aspartate aminotransferase, hematocrit, glucose, and uric acid) were also measured. Air particulate data showed significantly higher Mn levels (p<0.05) in the urban area (0.036 μg/m3) relative to the rural area (0.026 μg/m3). Mn concentrations were similar (P>0.05) in the two groups of pigeons for all the tissues except liver (Lachute=2.42 ppm; Montreal=3.13 ppm) and feces (Lachute=32.2 ppm; Montreal=46.8 ppm); the urban pigeons had about 35% more Mn than the rural pigeons. Aspartate aminotransferase (AST) was also significantly different in the two groups. These results show the importance of the entero-hepatic cycle in the homeostasis of Mn in blood and other tissues. Since the excess of Mn in the feces and liver of the urban pigeons relative to the rural pigeons was similar to the excess Mn in urban air over rural air, pigeon feces and liver appear to be good biomarkers of Mn contamination. Although it is premature to associate this excess Mn with the combustion of MMT, these results nevertheless lead us to consider the pigeon as an interesting indicator of the potential risk to the ecosystem and to human health.

Interference from uranium in neutron activation analysis or rare-earths in silicate rocks

Neutron activation analysis of rare-earth elements in silicate rocks containing several parts per million uranium may be complicated by interference from235U fission products and activation products of238U. The degree of interference has been measured quatitatively for La, Ce, Nd, Sm and Lu, and a method of correcting the NAA data for these elements is presented.

Bioaccumulation of manganese by plants: influence of MMT as a gasoline additive

Abstract This study on the bioaccumulation of manganese (Mn) by plants was motivated by the increased use of Methylcyclopentadienyl manganese tricarbonyl (MMT) as a replacement for lead in gasoline. Oats and beans were grown in sandy and organic soils at a control site (E o ) and at two other sites weakly (E + ) and highly exposed (E ++ ) to Mn contamination, potentially from a MMT source. Total Mn, Ca, Mg, Fe, Zn and Al were measured in the soils and in the plants (roots, stems/leaves and fruits). Exchangeable Mn was measured in the soils at the beginning and at the end of the exposure period. The pH of the organic and sandy silty soils were found to be lower outdoors (E + and E ++ ) than in the greenhouse (E o ) and exchangeable Mn was found to be significantly higher in the organic soil at E ++ (1.03–1.36 ppm). Higher Mn accumulation was also found in the fruits and stems of oats grown in the organic and sandy soils at E ++ . This Mn accumulation is often associated with increased Fe and Al in the plant. These results suggest that the addition of MMT to gasoline may result in an increase in exchangeable Mn in organic soils. However, it has not been proven that the source of the increased Mn accumulation is indeed MMT in gasoline.

Activation Constants for Slowpoke and MNS Reactors Calculated from the Neutron Spectrum and k0 and Q0 Values

The relative thermal, epithermal and fast neutron fluxes were measured in the inner and outer irradiation sites of three Slowpoke reactors and one Miniature Neutron Source (MNS) reactor by the bare triple monitor method. Using the measured neutron spectrum parameters and a compilation of published k0 and Q0 values, activation constants were calculated for the most intense gamma-rays of all nuclides commonly used in NAA. The resulting table of constants can be used to standardize NAA measurements for all elements when combined with relative efficiency measurements and the measurement of the thermal neutron flux with one standard. The observed constancy of the neutron spectra suggests that these activation constants are valid for all 14 Slowpoke and MNS reactors.

Manganese and other trace elements in urban snow near an expressway

The Mn contamination arising from the combustion of MMT (methylcyclopentadienyl manganese tricarbonyl) in unleaded gasoline was assessed using snow collected at different distances 15, 25, 125 and 150 m from an expressway (Montreal, Canada) in February 1993. The snow samples were analyzed by atomic absorption and by neutron activation for total Mn, Mg, Cu, V, Al, Zn, Fe, Na, and Ca concentrations in the soluble (<0.4 microm) and particulate fractions. ANOVA with ranked values was performed to compare element concentrations and soluble/particulate ratios among receptor sites and depths. Principal component analysis was used to describe the spatiotemporal variations of the deposition rates and the influence of meteorological factors. The average concentration of all trace elements, except Mg, Cu, and V, decreased significantly (p<0.05) from receptor sites near the road (15-25 m) to those farther away (125-150 m). The deposition rates of all metals and ions, except Cu, were highly positively correlated (tau = 0.5-0.9) with each other and inversely correlated with snowfalls. Wind frequency showed no correlation with deposition rate. The spatial trend was similar for all these elements making it difficult to distinguish Mn arising from the combustion of MMT from that due to other sources, such as road dust. Only the soluble/particulate ratio calculated for Mn seemed higher than that for the other metals, which might be explained by the particle size of Mn from MMT (0.2-0.4 microm). The present study only indicates a direct contamination of the snow by road activities and substantial deposition of trace elements near the roadway; no clear link can be established between motor vehicle emissions and the concentration of Mn in snow.

NAA with the improved relative method and the interactive computer program EPAA

The program EPAA has been written to perform neutron activation analysis calculations on a personal computer. It reads gamma-ray spectra from disk, calculates peak areas using interactive computer graphics, corrects interferences, and calculates the concentrations of the elements chosen by the user with the improved relative standardization method. This method is suitable for use with reactors with reproducible neutron fluxes. Calibrations are performed for all elements in standard counting geometries and are used for subsequent analyses over a long period of time.

ON-LINE FLOW VISUALIZATION IN MULTIPHASE REACTORS USING NEURAL NETWORKS

Abstract The success of the radioactive particle tracking system (RPT) developed at the Ecole Polytechnique (Montreal) and pplied to the study of particle motion in a variety of chemical reactors (three-phase fluidized bed, gas spouted bed and liquid fluidized bed) has motivated us to continue improving this technique (in terms of accuracy and resolution) and to apply it to new reactor types. Our goals are: (i) to enhance the original search location algorithm in order to permit on-line flow visualization and (ii) to extend RPT to very fast solids flows, such as those encountered in circulating fluidized beds (particle velocities higher than a few m s−1). The potential of neural networks for on-line and real-time visualization of particle movements in multiphase reactors will be illustrated. The original least-squares search location algorithm (Larachi et al., 1994) has been replaced with an enhanced algorithm which uses a three-layer feedforward neural network. The results obtained from the two algorithms for particle tracking in a three-phase fluidized bed reactor are compared. The RPT system employs 8 NaI(TI) scintillation detectors to study the movement of solid particles in chemical reactors. The performance of the system was investigated using particles containing the radioisotopes 46Sc (γ-ray energy 1005 keV), 99Mo (γ-ray energy 140 keV) and 198Au (γ-ray energy 412 keV). The three-dimensional spatial resolution was measured in empty and water-filled tubes, simulating highly diluted and dense media. The best results were obtained using 198Au with which the particle can be located to within 7 mm in water and 9 mm in air 100 times s−1.