Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: L. Brown x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

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.

Restricted access

The thermal decomposition of ammonium metavanadate

II The kinetics and mechanism of the decomposition

Journal of Thermal Analysis and Calorimetry
Authors: M. Brown, L. Glasser, and B. Stewart
Restricted access

It has been shown that the ESS Maximum Principle, used to find evolutionarily stable strategies, is applicable to a large class of population dynamic models. These include both differential and difference equation models. To date, this principle has been used to find an evolutionarily stable strategy (ESS) for single-stage systems. That is, systems in which the density of all individuals of a given species or phenotype are represented by a scalar. There are many situations in which more detail is needed in order to properly model the state of a system (e.g. within a given species or phenotype, juveniles may effect the fitness of adults and vice versa). In this case, the density of a species or phenotype is more properly represented by a vector. Each component of the vector represents the density of a particular life stage. We show here that the ESS Maximum Principle may be extended to include multistage systems in a very natural way. In the scalar case, we have used a scalar G-function (fitness generating function) to model the system and formulate the ESS Maximum Principle. We have shown that it is necessary for the G-function, when evaluated at equilibrium, to take on a maximum with respect to the ESS strategy. Here we show, for multistage systems that a G-matrix may be used to model the system and the ESS Maximum Principle may be stated in terms of a G-matrix. In this case the real part of the dominant eigenvalue of the G-matrix, when evaluated at equilibrium, must take on a maximum with respect to the ESS strategy. Two multistage examples are given to illustrate use of the theory.

Restricted access

Abstract  

Treating iron-doped ZSM-5 zeolite with NO2 produced a complete change in the parameters of its 57Fe Mössbauer spectrum. The intensity of the absorption showed a dramatic decrease at 40–70 K with smooth, but anharmonic, behavior above this temperature. The results can be interpreted in terms of the modification of the iron environment to form an approximately square-well potential. This results in an asymmetric potential in which the iron becomes frozen in one region at low temperatures.

Restricted access

Abstract  

The nuclear track technique (NTT) is used to enhance the porosity of silica micro-particles. The enhanced porosity is a result of the formation of surface and interior pores or tracks in the silica by the action of external and internal fission fragments. The fission tracks produced at the surface and within the interior of the micro-particles are a result of coating the particles with trace quantitities of uranium, instead of having trace quantities of uranium incorporated within the silica matrix.

Restricted access

Abstract  

Naturally occurring opals from three different regions in Australia were studied for their thermal characteristics. All the opals showed initial expansion followed by contraction in thermomechanical analysis (TMA) although the temperature at which the change from expansion to contraction occurred depended on their provenance. Thermogravimetric analysis (TG) revealed different rates and temperatures of dehydration for these opals. A general correlation between the temperature at which there was a zero thermal expansion and that of the maximum rate of dehydration was observed. A dehydration–sintering mechanism is proposed with the effect of sintering being more pronounced following total dehydration.

Restricted access

The thermal decomposition of ammonium metavanadate, III

A structural view of the decomposition mechanism

Journal of Thermal Analysis and Calorimetry
Authors: M. E. Brown, L. Glasser, and B. V. Stewart

The kinetics and thermodynamics of the thermal decomposition of ammonium metavanadate (AMV) are combined with the structural information available for AMV, for the important decomposition intermediate, ammonium hexavanadate (AHV), and for vanadium pentoxide, the product of the decomposition in non-reducing atmospheres, to enable the atomic movements involved in the course of decomposition to be discussed in detail.

Restricted access