This proposal deals with the development of a radiation detector system that will make possible the direct measurement of the structure of charged particle tracks in a gas. Such a detector will permit the measurement of energy e.g., the diameter of a DNA molecule. This information, which is critical to development and evaluation of mechanistic biophysical models for understanding radiation effects, has hereto fore not been measurable. When a charged particle penetrates a gas, electrons produced during ionization events quickly become thermalized. The proposed detector system will determine the positions and number of these electrons by imposing a suitable RF field, causing the electrons to agitate and excite molecules of the gas which will then fluoresce producing photons that will be detected by the external optical detector system. Thus, each point of light will represent the position of a single electron. In Phase I experimental proof of the concept was made that a single charged particle track can be detected optically. In this proposal the operation of the system would be greatly enhanced so that CCD detectors can be used to obtain quantitative information from images of all of the electrons produced in the track of a single particle.
