A NEW DEVICE FOR MICRODOSIMETRY

THIS PROPOSAL DEALS WITH THE DEVELOPMENT OF A RADIATION DETECTOR TO MAKE POSSIBLE THE DIRECT MEASURMENT OF THE STRUCTURE OF CHARGED-PARTICLE TRACKS IN A GAS. SUCH A DETECTOR WILL PERMIT THE MEASUREMENT OF MICRODOSIMETRIC DISTRIBUTIONS IN VOLUMES THAT CORRESPOND TO NANOMETERS IN A BIOLOGICAL CELL, E.G., THE DIAMETER OF A DNA MOLECULE. WHENA CHARGED PARTICLE PENETRATES A GAS, ELECTRONS PRODUCED DURING IONIZATION QUICKLY BECOME THERMALIZED. THE PROPOSED DETECTOR WOULD DETERMINE THE POSITIONS OF ALL OF THESE ELECTRONS BY IMPOSING A SUITABLE RADIO FREQUENCY FIELD, CAUSING THE ELECTRONS TO AGITATE AND EXCITE MOLECULES OF THEGAS, WHICH WOULD THEN FLUORESCE AND PRODUCE PHOTONS THAT COULD BE DETECTED BY AN EXTERNAL OPTICAL DETECTOR. THUS, EACH POINT OF LIGHT WOULD REPRESENT THE POSITION OF A SINGLEELECTRON. IN PHASE I, AN EXPERIMENTAL PROOF OF CONCEPT WILL BE MADE THAT A SINGLE CHARGED-PARTICLE TRACK COULD BE DETECTED OPTICALLY. IN PHASE II, VIDICON OR OTHER CCD DETECTORS WILLBE USED TO OBTAIN SPATIALLY RESOLVED IMAGES OF ALL OF THE ELECTRONS PRODUCED IN THE TRACK OF A SINGLE CHARGED PARTICLE.