LIQUID XENON MULTIWIRE PROPORTIONAL CHAMBERS FOR NUCLEAR MEDICINEAPPLICATIONS

The need for improved spatial resolution in nuclear medicine has long been recognized. Notable attempts to achieve this goal are the gas-filled wire chambers and solid-state detectors. (1) However, at energies above 100 keV, gas-filled chambers suffer from poor detection efficiency and a long recoil electron range in the gas. While it is advantageous to pressurize these chambers to 10 or more atmospheres, structural design of the thin window presents a formidable task. High-resolution optimal collimators do not appear to have sufficient strength to be used as a pressure support window. Solid-state detectors, while having the potential of a gamma camera with a superb energy resolution, are presently studied on a very small scale due to technological and cost limitations. Aside from the detector, the parallel-hole collimator presents a real limit to the resolution of the camera. A factor of two improvement in the resolution results in a factor of four loss in the collimator's transmission. A careful analysis of optimal collimators and the application of collimators designed for a specific depth range and resoluation are part of our overall program. Our goal has been the development of a liquid-xenon multiwire gamma camera with 2- to 3-mm spatial resolution, high counting-rate performance, high sensitivity, and the potential for scaling-up in size. Important ingredients for successful imaging in the prototype chamber discussed in this paper were the discovery of electron multiplication in liquid xenon, (2) the development of reliable purification techniques, (3) and the ability to extract electrons from the liquid into the gaseous phase. This paper is specifically addressed to the subject of detector development with liquid-xenon totally-filled chambers and recent work with dual-phase chambers in which the {gamma} rays are converted in the liquid phase and are electronically detected in the gaseous phase