Feasibility of a novel TLD based personal microdosimeter for dosimetry and risk assessment of astronauts enduring long-term habitat in space stations

摘要

The ratio of thermoluminescence glow curve area of LiF and BeO dosimeters is found to be directly proportional to average LET (linear energy transfer) of impinging radiations. Using this phenomenon and widely available TLD-700 (~7LiF: Mg, Ti) and BeO (Thermolux) dosemeter chips the authors have developed a TLD-Microdosimeter (LiBe-14) emulating a gas filled Tissue Equivalent Proportional Counter (TEPC), an essential tool of space radiation dosimetry. The LiBe-14 is capable of assessing the average LET (L_(av): 11.0 to -100 keVμm~(-1)), quality factor (Q_(av): 1.1 to -30) and associated dose equivalent (H: 0.1 to 1000 mSv) of complex radiation fields of interest similar to space radiations predominant in Low Earth Orbit (LEO) environment. The microdosimeter was calibrated using the mixed radiation fields produced by bombarding a 25cmx25cmx35cm polystyrene phantom with 81, 119, 150 177, 201 and 231 MeV protons from a Proton Therapy Medical Cyclotron and a Rossi-Type TEPC. Presently, there are two space stations in operation at LEO: (a) Shenzhou-XI (Apogee-altitude: 378km, Inclination: 42.79°, 16 orbits/day), (b) International Space Station (ISS) (Apogee-altitude: 400km, Inclination: 51.64°, 15.5 orbits/day). Astronauts of both genders and of various age groups use to reside in those space stations for durations ranging from few weeks to several months depending on mission goals. Due to the complex nature of space radiation inside the space station, personal monitoring of the astronauts is performed by using "multi-component" dosimeters made of batches of different types of TLD and CR-39 track etch detector to assess the sparsely and densely ionising radiation respectively. This paper highlights the feasibility of LiBe-14 personal microdosimeter based on TLD-700 and BeO chips for estimation of dose equivalent and associated radiation risk of astronauts working in LEO space stations.