Research Project
3491698
A program is proposed for the development of a thermoluminescence dosimetry (TLD) system for measurement of absorbed dose distributions of ionizing radiation (gammas, betas, neutrons) in phantoms. The system will employ IST-developed technology for laser heating and fabrication of suitable large area thin film dosimeter arrays. Commercial TL phosphors (e.g. magnesium borate) will be used with a printing technique for producing various spot sizes and thicknesses on thin glass or high-temperature polymer substrate sheets. Neutron doses can be measured using proton radiators and proton absorbers on alternate spots, or using a TL phosphor made with different isotopes at alternate locations, for gamma-neutron discrimination. This LTD system will be based on a highly stable, closed-loop feedback controlled 20 Watt CO2 laser whose beam has a uniform cross section of variables size. The temporal shape of the laser heating pulse will be tailored by computer control for pre- and post-anneal treatments and rapid heating of these dosimeters with minimal incandescence background emission. A large reading area will be obtained by the addition of special X-Y dosimeter positioning mechanisms. The advantage of the proposed technology over conventional phantom dosimetry is the possibility of placing a large number of very small dosimeters in form of arrays on sheets between the transverse slices of human phantoms (or even wrapping them around bone-like or prosthetic material inserted in these phantoms) and rapidly measuring the absorbed doses in an automated TLD reader (potentially over 8000 dosimeter spots per hour). The dose distributions will be plotted using specially developed software.
