Accelerator Mass Spectrometry and Bayesian Data Analysis

Accelerator mass spectrometry (AMS) is an ultrasensitive technique for measuring the concentration of a single isotope. The electric and magnetic fields of an electrostatic accelerator system are used to filter out other isotopes from the ion beam. The high velocity means that molecules can be destroyed and removed from the measurement background. As a result, concentrations down to one atom in 10^16 atoms are measurable. This thesis describes the construction of the new AMS system in the Accelerator Laboratory of the University of Helsinki. The system is described in detail along with the relevant ion optics. System performance and some of the 14C measurements done with the system are described. In a second part of the thesis, a novel statistical model for the analysis of AMS data is presented. Bayesian methods are used in order to make the best use of the available information. In the new model, instrumental drift is modelled with a continuous first-order autoregressive process. This enables rigorous normalization to standards measured at different times. The Poisson statistical nature of a 14C measurement is also taken into account properly, so that uncertainty estimates are much more stable. It is shown that, overall, the new model improves both the accuracy and the precision of AMS measurements. In particular, the results can be improved for samples with very low 14C concentrations or measured only a few times.

Use of Standards for CAD Layers in Building

One of the central issues in making efficient use of IT in the design, construction and maintenance of buildings is the sharing of the digital building data across disciplines and lifecycle stages. One technology which enables data sharing is CAD layering, which to be of real use requires the definition of standards. This paper focuses on the background, objectives and effectiveness of the International standard ISO 13567, Organisation and naming of layers for CAD. In particular the efficiency and effectiveness of the standardisation and standard implementation process are in focus, rather than the technical details. The study was conducted as a qualitative study with a number of experts who responded to a semi-structured mail questionnaire, supplemented by personal interviews. The main results were that CAD layer standards based on the ISO standard have been implemented, particularly in northern European countries, but are not very widely used. A major problem which was identified was the lack of resources for marketing and implementing the standard as national variations, once it had been formally accepted.