Semiconductor particle detectors are ideal for alpha spectroscopy due to their compact size, low noise, and high resolution.
This paper describes the construction and testing of an automatic sample changer for use with such a detector. The changer
was constructed from locally available services and materials. It holds up to 24 samples of alpha emitting material deposited
on 22 mm stainless steel counting planchets. The vacuum chamber can be evacuated to less than 10 μm mercury in 10 to 15 minutes.
Once the chamber has been evacuated and detector bias has been applied, any sample in the chamber may be selected for analysis,
either automatically or manually. Continuous automatic analysis of up to 24 samples is possible. Variation in efficiency from
position to position was found to be 3.25% at the detector-sample spacing of 4.8 mm, and 2.31% at 27 mm. Shielding between
the adjacent samples not under analysis and the detector was acceptable.
Nutrigenomics examines nutrient-gene interactions on a genome-wide scale. Increased dietary fat or higher non-esterified fatty acids (NEFA) from starvation-induced mobilisation may enhance hepatic oxidation and decrease esterification of fatty acids by reducing the expression of the fatty acid synthase gene. The key factors are the peroxisome proliferator-activated receptors (PPARs). Dietary carbohydrates — both independently and through insulin effect — influence the transcription of the fatty acid synthase gene. Oleic acid or n-3 fatty acids down-regulate the expression of leptin, fatty acid synthase and lipoprotein lipase in retroperitoneal adipose tissue. Protein-rich diets entail a shortage of mRNA necessary for expression of the fatty acid synthase gene in the adipocytes. Conjugated linoleic acids (CLAs) are activators of PPAR and also induce apoptosis in adipocytes. Altered rumen microflora produces CLAs that are efficient inhibitors of milk fat synthesis in the mammary gland (‘biohydrogenation theory’). Oral zinc or cadmium application enhances transcription rate in the metallothionein gene. Supplemental CLA in pig diets was found to decrease feed intake and body fat by activating PPARγ-responsive genes in the adipose tissue. To prevent obesity and type II diabetes, the direct modulation of gene expression by nutrients is also possible. Nutrigenomics may help in the early diagnosis of genetically determined metabolic disorders and in designing individualised diets for companion animals.
Sodium silicate, or a mixture of silica and sodium carbonate, reacts with chromium(III) oxide in the presence of oxygen to give sodium chromate, within the approximate temperature range 300–900°. Above 900° the reaction is reversed and chromium(III) oxide regenerated.
The thermal behaviour of Ba[Cu(C2O4)2(H2O)]·5H2O in N2 and in O2 has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively
low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place
in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation
of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The
enthalpy for the dehydration was found to be 311±30 kJ mol−1 (or 52±5 kJ (mol of H2O)−1). The overall enthalpy change for the decomposition of Ba[Cu(C2O4)2] in N2 was estimated from the combined area of the peaks of the DSC curve as −347 kJ mol−1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly
deceleratory and the α-time curves could be described by the three dimensional diffusion (D3) model. The values of the activation
energy and the pre-exponential factor for the dehydration were 125±4 kJ mol−1 and (1.38±0.08)×1015 min−1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed
in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry
model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.
The values ofEa andA were 206±23 kJ mol−1 and (2.2±0.5)×1019 min−1, respectively, for the fast process, and 259±37 kJ mol−1 and (6.3±1.8)×1023 min−1, respectively, for the slow process.
We prove the following theorem. Assume f ∈ L∞(R2) with bounded support. If f is continuous at some point (x1,x2) ∈ R2, then the double Fourier integral of f is strongly q-Cesro summable at (x1,x2) to the function value f(x1,x2) for every 0 < q < ∞. Furthermore, if f is continuous on some open subset
The effect of electrolysis on the devitrification of aluminosilicate glasses containing 2–10 wt. % Ti, V, Fe, Co and Ni was studied by DTA. In all cases the devitrification temperature is lowered under electrolysis by an amount greater than that which would be achieved by independently electrolysing or doping with the transition metal ion. The relative effect of the different transition metal ions on devitrification is explained in terms of the strengths of the respective metal-oxygen bonds and the octahedral/tetrahedral site preferences of the ions. The electrolysis mechanism is similar to that of the undoped base glass, but also includes migration of the transition metal ions to the cathode and the possibility of interaction between these species and the residual protons of the base glass.
Authors:A. Coetzee, M. Brown, D. Eve, and C. Strydom
Both isothermal and programmed temperature experiments have been used to obtain kinetic parameters for the dehydrations and
the decompositions in nitrogen of the mixed metal oxalates: FeCu(ox)2·3H2O, CoCu(ox)2·3H2O and NiCu(ox)2·3.5H2O, [ox=C2O4]. Results are compared with those reported for the thermal decompositions of the individual metal oxalates, Cuox, Coox·2H2O, Niox·2H2O and Feox·2H2O. X-ray photoelectron spectroscopy (XPS) was also used to examinee the individual and the mixed oxalates.
Dehydrations of the mixed oxalates were mainly deceleratory processes with activation energies (80 to 90 kJ·mol−1), similar to those reported for the individual hydrated oxalates. Temperature ranges for dehydration were broadly similar
for all the hydrates studied here (130 to 180°C).
Decompositions of the mixed oxalates were all complex endothermic processes with no obvious resemblance to the exothermic
reaction of Cuox, or the reactions of physical mixtures of the corresponding individual oxalates.
The order of decreasing stability, as indicated by the temperature ranges giving comparable decomposition rates, was NiCu(ox)2>CoCu(ox)2>FeCu(ox)2, which also corresponds to the order of increasing covalency of the Cu−O bonds as shown by XPS.
Authors:D. Robertson, V. Thomas, H. Rieck, D. Haggard, W. Reece, J. Pappin, W. Hensley, D. Brown, C. Thomas, and P. Robinson
Battelle, Pacific Northwest Laboratories has recently developed, tested and field-demonstrated a technology for the direct assay of transuranic radionuclides (TRU), fission products, and activation products in a variety of radwaste packages generated at commercial nuclear power plants. This technology involves non-destructive passive neutron counting for determination of nanocurie/gram quantities of the TRU radionuclides. Direct gamma spectrometry combined with thermoluminescent dosimetry (TLD) and correlation analysis is also utilized to determine the concentrations of the fission and activation products present in the radwaste packages. Employing counting times of 10 to 20 minutes, a complete analysis of all radionuclides specified for assay by the U.S. Nuclear Regulatory Commission (in 10CFR61) prior to shallow-land disposal of commercial radwastes can be measured at concentrations at least tenfold below the least restrictive Class A waste catagory.
Authors:O. Manuel, J. Lee, D. Ragland, J. Macelroy, Bin Li, and W. Brown
Formation of the Solar System from heterogeneous debris of a supernova (SN) that exploded 5 billion years ago was recorded
as (1) inter-linked chemical and isotopic heterogeneities in meteorites, (2) higher levels of extinct nuclides in grains that
trapped larger isotopic anomalies, (3) the physical properties of grains mentioned in part (2), and (4) patterns of isotopic
anomalies in meteorites, in the solar-wind, and in solar flare particles. The Sun formed on the SN core, and planets formed
in a rotationally-supported, equatorial disk of SN debris. Interiors of the Sun and the inner planets accreted first in a
central, Fe-rich region surrounding the SN core. These were layered as condensate from other parts of the SN fell toward the
condensing Sun. Elements in outer SN layers formed low-density, giant Jovian planets. Intra-solar diffusion enriches hydrogen
and lighter isotopes of individual elements at the Sun's surface.