Dose dependence of F-centre production by fast neutrons in magnesium oxide

The effects of various thermal treatment methods on the radiation catalytical effects, induced by the pre-irradiation of the BASF K-3-10 catalyst by the γ- or β-radiation or by fast neutrons, were investigated. It has been found that the calcination of the irradiated non-reduced catalyst results in a strong decrease or even in total disappearance of the final radiation catalytical effects; however, at the same time the catalytical activity of the unirradiated catalyst was found to increase. The calcination of the catalysts in nitrogen atmosphere after reduction led also to a substantial decrease of the resulting positive radiation catalytical effects and exceeding a certain calcination temperature resulted in the decrease even of the unirradiated catalyst activity. It could be concluded that the calcination in nitrogen of the reduced irradiated samples decreases the radiation catalytical effects less than the calcination on air of the non-reduced irradiated samples. In both cases a different thermal stability of effects induced by different types of the ionizing radiation has been observed and it has been found that it increases in the sequence beta radiation – gamma radiation – fast neutrons. The investigation of the γ radiation dose dependence of the radiation catalytical effect on the catlyst calcinated before irradiation under the access of air showed that the final radiation catalytical effects are lower than those observed in the case of similarly irradiated but non-calcinated samples. At the same time the dose dependence of the effect has the same character in both cases.

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Effect of ionizing radiation on the kinetics of reduction of NiO-MgO mixed oxids with hydrogen

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19791023 ◽

1979 ◽

Vol 44 (4) ◽

pp. 1023-1033 ◽

Cited By ~ 5

Author(s):

Milan Pospíšil ◽

Miroslav Tvrzník

Keyword(s):

Nickel Oxide ◽

Magnesium Oxide ◽

Reaction Rate ◽

Mixed Oxides ◽

Reduction Rate ◽

Inert Atmosphere ◽

Fast Neutrons ◽

Mixed System ◽

Degree Of Reduction ◽

Kinetics Of

The low-temperature reduction of the mixed system nickel oxide-magnesium oxide with hydrogen was studied thermogravimetrically in the region 260-470 °C. The two oxides form in the whole composition region solid solutions, some physicochemical parameters of which vary nonmonotonically with the sample composition. The kinetics and degree of reduction of nickel oxide are appreciably affected by the presence of the unreduced magnesium oxide, in higher concentrations lowering the reaction rate. The kinetics of the reduction can be quantitatively described by the equation 1-(1-α)1/3 = kt, valid in dependence on the composition in differently wide ranges of the degree of reduction α. The reaction rate can be varied, particularly for samples with low contents of magnesium oxide, by heat treatment in inert atmosphere at 700 °C, and for all samples by irradiation by gamma rays or fast neutrons. The reduction rate grows with the increasing content of magnesium oxide up to a constant value. The positive effect increases with the increasing gamma dose and, according to the kind of radiation, in the order γ, n. The variation of the reactivity of irradiated or thermally treated mixed oxides is due predominantly to the shift of the equilibrium of the lattice defects, formation and stabilization of new centres, which affect the rate of nucleation of the forming metal phase.

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On the possibility of using magnesium oxide for selective detection of fast neutrons

Radiation Effects and Defects in Solids ◽

10.1080/10420150.2018.1424849 ◽

2018 ◽

Vol 173 (3-4) ◽

pp. 223-231 ◽

Cited By ~ 1

Author(s):

V. G. Kvatchadze ◽

V. T. Gritsyna ◽

M. G. Abramishvili ◽

G. G. Dekanozishvili ◽

M. V. Galustashvili ◽

...

Keyword(s):

Magnesium Oxide ◽

Fast Neutrons ◽

Selective Detection

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Observations of the Thermal Decomposition of Brucite

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101980 ◽

1968 ◽

Vol 26 ◽

pp. 446-447

Author(s):

P. L. Burnett ◽

W. R. Mitchell ◽

C. L. Houck

Keyword(s):

Thermal Decomposition ◽

Magnesium Oxide ◽

Basal Plane ◽

Magnesium Ions ◽

A Value ◽

Reaction Proceeds

Natural Brucite (Mg(OH)2) decomposes on heating to form magnesium oxide (MgO) having its cubic ﹛110﹜ and ﹛111﹜ planes respectively parallel to the prism and basal planes of the hexagonal brucite lattice. Although the crystal-lographic relation between the parent brucite crystal and the resulting mag-nesium oxide crystallites is well known, the exact mechanism by which the reaction proceeds is still a matter of controversy. Goodman described the decomposition as an initial shrinkage in the brucite basal plane allowing magnesium ions to shift their original sites to the required magnesium oxide positions followed by a collapse of the planes along the original <0001> direction of the brucite crystal. He noted that the (110) diffraction spots of brucite immediately shifted to the positions required for the (220) reflections of magnesium oxide. Gordon observed separate diffraction spots for the (110) brucite and (220) magnesium oxide planes. The positions of the (110) and (100) brucite never changed but only diminished in intensity while the (220) planes of magnesium shifted from a value larger than the listed ASTM d spacing to the predicted value as the decomposition progressed.

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Electron Beam-Induced Mass Loss in Freeze-Dried Tissue and Protein Samples

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010011917x ◽

1985 ◽

Vol 43 ◽

pp. 470-471

Author(s):

M.E. Cantino ◽

M.K. Goddard ◽

L.E. Wilkinson ◽

D.E. Johnson

Keyword(s):

Electron Beam ◽

Salivary Gland ◽

Mass Loss ◽

Counting Rate ◽

Dose Dependence ◽

X Ray ◽

Large Samples ◽

Freeze Dried ◽

Muscle Homogenate ◽

Large Muscle

Quantification in biological x-ray microanalysis depends on accurate evaluation of mass loss. Although several studies have addressed the problem of electron beam induced mass loss from organic samples (eg., 1,2). uncertainty persists as to the dose dependence, the extent of loss, the elemental constituents affected, and the variation in loss for different materials and tissues. in the work described here, we used x-ray counting rate changes to measure mass loss in albumin (used as a quantification standard), salivary gland, and muscle.In order to measure mass loss at low doses (10-4 coul/cm2 ) large samples were needed. While freeze-dried salivary gland sections of the required dimensions were available, muscle sections of this size were difficult to obtain. To simulate large muscle sections, frog or rat muscle homogenate was injected between formvar films which were then stretched over slot grids and freeze-dried. Albumin samples were prepared by a similar procedure. using a solution of bovine serum albumin in water. Samples were irradiated in the STEM mode of a JEOL 100C.

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Time-resolved high-resolution electron microscopy of structural stability in mgo clusters

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100165823 ◽

1996 ◽

Vol 54 ◽

pp. 672-673

Author(s):

T. Kizuka ◽

N. Tanaka

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Magnesium Oxide ◽

Structural Stability ◽

High Resolution Electron Microscopy ◽

Video Tape ◽

Solid State Physics ◽

Time Resolved ◽

Resolution Electron ◽

Structural And Functional Properties

Structure and stability of atomic clusters have been studied by time-resolved high-resolution electron microscopy (TRHREM). Typical examples are observations of structural fluctuation in gold (Au) clusters supported on silicon oxide films, graphtized carbon films and magnesium oxide (MgO) films. All the observations have been performed on the clusters consisted of single metal element. Structural stability of ceramics clusters, such as metal-oxide, metal-nitride and metal-carbide clusters, has not been observed by TRHREM although the clusters show anomalous structural and functional properties concerning to solid state physics and materials science.In the present study, the behavior of ceramic, magnesium oxide (MgO) clusters is for the first time observed by TRHREM at 1/60 s time resolution and at atomic resolution down to 0.2 nm.MgO and gold were subsequently deposited on sodium chloride (001) substrates. The specimens, single crystalline MgO films on which Au particles were dispersed were separated in distilled water and observed by using a 200-kV high-resolution electron microscope (JEOL, JEM2010) equipped with a high sensitive TV camera and a video tape recorder system.

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