Development of position-sensitive tissue equivalent proportional chamber for space dosimetry

Radiation effects on human body are evaluated using dose equivalent H, defined as the product of the absorbed dose and the quality factor given as a function of LET. In space, there exist many kinds of radiations, such as galactic cosmic rays and geomagnetic trapped particles, where charged particles and neutrons are the main components contributing to radiation dose in space. Since LET of these radiations widely distributes, it is essential to measure directly LET for evaluation of H in space. The Tissue Equivalent Proportional Counter (TEPC) has been used as a standard space dosimeter, which is a simple gas counter made of tissue equivalent materials. In TEPC, since no position information is given, a lineal energy is measured instead of LET. Obviously the lineal energy does not represent LET accurately. The dose obtained using TEPC is reported to be inconsistent with those measured with real LET spectrometers. We started to develop a new dosimeter named as Position Sensitive Tissue Equivalent Chamber (PS-TEPC), which is based on a time projection chamber using Micro Pixel Chamber (mu-PIC) as two- dimensional position-sensitive detector. In this study, we aim to demonstrate feasibility of PS-TEPC and to complete a prototype of PS-TEPC usable in space. The performance was tested by using the heavy ion beams to examine its abilities of 3D-tracking and energy measurement.