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 LET∞H 2O 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. ► We demonstrate the two-step etching method for control of CR-39 sensitivity. ► PEW solution makes effectively to reduce CR-39 sensitivity but produce fuzzy track. ► Post-etching by NaOH solution recovers the track shape. ► Response curve varies as a function of ethanol concentration of pre-etching by PEW. ► Two-step etching makes increase of LET detection threshold up to 66 keV/μm.