PEW-NaOH二段階エッチング法を用いたCR-39の応答感度制御

CR-39 PNTDs are commonly used as the heavy ion detectors with the LET detection threshold of > ~5 keV/um in water. In the space utilization field, CR-39 PNTDs onboard the International Space Station (ISS) are used as the space radiation dosimeter to measure precisely LET distribution of cosmic rays and also CR-39 is a promising candidate detector for the precise observation of trans-iron nuclei in galactic cosmic rays (GCRs). However, due to the high sensitivity of CR-39 detector, a single track of ultra heavy trans-iron nuclei will not be discernible among the numerous background tracks produced by lighter nuclei such as CNO group and Fe in GCRs. Moreover, the detector response will be saturated in higher LET (i.e. trans-iron nuclei) regions. Raising the LET detection threshold of CR-39 and controlling the detector response to be high enough at the arbitrary LET regions will be able to observe trans-iron nuclei selectively without recording low LET particles such as C, N, O nuclei that are dominant heavy components in GCRs. We found that the two-step etching method using PEW (Potassium hydroxide + Ethanol + Water) solution for pre-etching and 7N NaOH solution for post-etching increases the detection threshold and improves the charge resolution for high LET particles in CR-39. In this paper, we report a method to control the detector response and detection threshold of CR-39 PNTDs using the two-step etching process to achieve the precise measurement of high LET particles.第26回固体飛跡検出器研究