||Dosimetry of proton-induced target fragments with CR-39 PNTD and AFM
Kawashima, Hajime ,
High energy protons, the main component of the cosmic rays, dominates the radiation risk for astronauts in space. Although the linear energy transfer (LET) of energetic protons is lower than that of heavy ions, their flux is extremely high in the cosmic rays. Results of space radiation dosimetry experiments using CR-39 plastic nuclear track detectors (PNTD) show that the contribution of proton-induced secondary particles to total absorbed dose and dose equivalent received by astronauts during space missions is significant. In addition to energy loss by ionization processes energetic protons can undergo nuclear interactions with target nuclei of Z >1, resulting in the production of short range (<10 µm), high-LET target fragment particles. One of the few methods to detect these short-range particles is by means of CR-39 PNTD analyzed with an atomic force microscope (AFM). For the evaluation of the short-range, high LET target fragment contribution to total dose, CR-39 (BARYOTRAK) PNTDs were irradiated with 30 - 230 MeV protons at HIMAC and cyclotron facilities in NIRS. CR-39 PNTDs are insensitive to primary protons of these energies due to the LET detection threshold of CR-39. Sets of CR-39 PNTD were exposed at six different incident angles to take into account the intrinsic sensitivity of the critical angle for track registration of the detector. Following irradiation and chemical processing, LET spectrum between 15 and 1500 keV/m was measured in each detector set by means of AFM. In this presentation the dose contribution of secondary particles for primary protons and its energy dependency will be presented.
Space Radiation and Heavy Ions in Therapy Symposium 2015 (SRHITS2015)