Spatial distribution and high LET component of absorbed dose measured by passive radiation monitors in ISS Russian segment N. Yasuda, H. Kawashima, M. Kurano, Y. Uchihori, H. Kitamura (NIRS) Yu. Akatov, V. Shurshakov (IMBP) I. Jadrnickova, F. Spurny (NPI) I. Kobayashi (Nagase Landauer, Ltd.) H. Ohguchi, Y. Koguchi (Chiyoda Technol Corporation)
BRADOS experiment We conducted an intercomparison experiment for passive radiation dosimeters, Space Intercomparison/BRADOS, • aboard the International Space Station (Russian • Service Module ). Phase-2 • Spatial distributions of dose (rate) at 5 locations • Intercomparison for dosimeters of NIRS and IBMP • Exposure duration: 268.5 days • This experiment was performed in the frame work of • ICCHIBAN project.
Passive dosimeter (NIRS) TLD layer Luminescence detectors: low LET CR-39: high LET ≥ 5 keV/mm
Shielding functions in the Service Module model Less Shielded Most Shielded Service Module
Results 1 Spatial distributions ~31g/cm2 ~40g/cm2
Dose quantities are depending on local shielding environment.
Comparison RRMD and CR-39 Both results are in good agreement when they pick up only cone-shaped etch pits. Tawara, Doke et al., RM35(2002)119.
Cone-shaped Track Well-behaved Track Well-behaved Stopper Track Over-Etched Stopper Track Track Taxonomy: Representative Sample
Estimation of dose contribution of short range particles • AFM Short bulk etch ~ 1 mm • Different types of CR-39 detectors Different detection threshold (HARZLAS TD-1 for >5 keV/mm) (BARYOTRAK for higher LET particles)
Calibration curves for different types of CR-39 Pure CR-39 + anti-oxidant Pure CR-39 200eV 200eV LET Threshold ~ 50 keV/mm LET Threshold ~ 5 keV/mm
HARZLAS TD-1 B=18 mm
BARYOTRAK B=19 mm
BARYOTRAK B=19 mm
How to estimate • For results of BARYOTRAK, • The component of cone shape track is in good agreement with • TD-1 detector. • Assumption: • all the shallow track (green) has LET = 50 keV/mm • (Threshold LET: minimum case)
Results Dose: x 1.7 (at least) Dose eq: x 2.5 (at least) QF: x 1.8 (at least)
Conclusions • Dose quantities seem to be depending on local shielding environment. • Contribution of short range tracks was estimated with assumption (all shallow tracks = 50 keV/mm). to dose (x 1.7) to dose eq (x 2.5) to averaged QF (x 1.8) (at least) • Contribution of short range tracks seems to be significant for dose and dose eq. - need further systematic study coupled with accelerator exp. (ICCHIBAN) - need some clear definitions/guide line to verify dose amounts by CR-39 - need model calculations
R-16 detector 0.5 g/cm2 3.5 g/cm2 SI1 This exp. MATROSHKA-1 Autumn 2005
Detectors • R-16 (1 location) with Pille-ISS • DB-8 (4 locations) • BRADOS BOX (5 locations) from IBMP - TLD LiF:Mg,Ti from NIRS - TLD LiF:Mg,Ti - Luxel OSL - Glass detector - CR-39 (HARZLAS TD-1, BARYOTRAK) *One box was located near the R-16 detector. *Two Pilles were located on the R-16 detector.
Overview of presentation • Spatial dose distribution (5 locations in Russian Service Module) • Comparison of luminescence detector and on board monitors (R-16, DB-8 and Pille-ISS) • Contribution of short range particle to dose and dose equivalent
Results * DB-8 monitors: 264, 208, 219, 146 mGy/day ~±30% ~±20% Difference ~20%
Relevant Facts concerning Galactic Cosmic Radiation • GCR consists of 87% protons, 11% helium nuclei (a-particles) and 1% heavy ions (Z³3). • While heavy ions are only 1% of flux, they make a significant (>25%) contribution to total dose equivalent. • Intensity of GCR is inversely proportional to level of solar activity throughout the 11 year Solar Cycle. • GCR is omnidirectional and isotropic. • Much of the GCR component is too energetic to practically shield (e.g. surrounding the spacecraft with polyethylene). • Leads to constant (chronic), low dose rate. - GCR produce secondary nuclei by nuclear reactions with shielding materials / inside body. - Short range and higher LET component will not be appeared in the active detector devices.