Detection threshold control of CR-39 plastic nuclear track detectors for the selective measurement of high LET secondary charged particles

The two-step etching method using PEW (Potassium hydroxide + Ethanol + Water) and NaOH solutions was applied to the control of the response of CR-39 plastic nuclear track detectors for the measurement of high LET (linear energy transfer) particles. CR-39 detectors were exposed to several heavy ion beams covering the LETH₂O range of 30-750 keV/μm from HIMAC (Heavy Ion Medical Accelerator in Chiba) at NIRS (National Institute of Radiological Sciences), Japan. The detectors were pre-etched in PEW solutions with 3 different ethanol concentrations at the temperature of 70 °C for 30-60 min. Then, the detectors were post-etched in 7N NaOH solution at the same temperature for 4-28 h. We found that the response curves and the detection thresholds of the detectors smoothly shifted to higher LET regions as the ethanol concentration increases in PEW solution.