Nelson Ng

High dose-rate brachytherapy source localization: positional resolution using a diamond detector

A potential real-time source position verification process for high dose-rate (HDR) brachytherapy treatment is described. This process is intended to provide immediate confirmation that a treatment is proceeding according to plan, so that corrective action can be taken if necessary. We show that three dosimeters are in principle sufficient and demonstrate the feasibility of the process using a diamond detector and an Ir-192 source. An error analysis including all identified sources of error shows that this detector is capable of locating the distance to the source to within 2 mm for distances up to 12 cm. This positional accuracy is less than the diameter of typical HDR catheters indicating that a diamond detector can be used to accurately determine the distance to the source. The uncertainty in the distance is found to increase with distance.

Photodesorption of gases in vacuum glazing

When samples of vacuum glazing are exposed to sunlight, the pressure within these devices is observed to increase. The major gas species released have been identified using mass spectroscopic techniques, and are found to be carbon monoxide and carbon dioxide rather than water vapor as in thermally degraded vacuum glazing. Different measuring techniques, including the use of a spinning rotor gauge, were developed to study the time dependence of pressure in samples of vacuum glazing during sunlight exposure. The mechanism associated with optical stability of vacuum glazing has been studied. High temperature baking during the evacuation stage of the manufacturing process for vacuum glazing greatly improves the stability of these devices under optical illumination.

Bakeable, all-metal demountable vacuum seal to a flat glass surface

A technique is described for making a demountable vacuum seal of reasonably good quality between an all-metal evacuation cup and a flat glass surface. The seal is bakeable to temperatures close to the softening point of glass. The stainless steel evacuation cup has two concentric and coplanar sealing surfaces. The regions defined by these surfaces are differentially pumped. Pressures typically below 1 Torr are achieved in the annular space between the two sealing surfaces using a conventional rotary pump. The center region inside the inner sealing surface is typically evacuated to below 10−4 Torr using conventional diffusion or turbomolecular pumps.

Impact of a composite metal-glass system; a study using high-speed imaging

In many large and small scale devices metal and glass are used side-by-side. In general, metal components are coupled directly to glass components to provide extra strength. However, in certain configurations the metal-glass interface is a structural weak point. This is particularly the case when the composite metal-glass systems are subjected to impact loading. In this work the impact, and subsequent failure, process of a simply layered glass-metal-glass composite structure was investigated. The structure consisted of a core array of cylindrically shaped metal separators sandwiched between two flat sheets of soda-lime glass. High speed photography was used to capture the impact process, and the subsequent failure, of the composite. Even though significant damage was sustained at the impact point, the high speed photography showed that the initial failure point was not at the impact point.