Annual Report

62. Effective Dose Equivalent on the Ninth Shuttle-Mir mission (STS-91)

Hiroshi Yasuda, Tatsuto Komiyama* and Kazunobu Fujitaka (* National Space Development Agency of Japan)

Keywords: space radiation, effective dose equivalent, Shuttle-Mir mission, organ and tissue doses, low Earth orbit


Organ and tissue doses and effective dose equivalent were measured using a life-size human phantom in the 9th Shuttle-Mir Mission (STS-91), a 9.8-day spaceflight at a low Earth orbit (about 400 km in altitude and 51.65oC in inclination). The doses were measured at 59 positions by a combination of thermoluminescent dosemeters of Mg2SiO4:Tb (TDMS) and plastic nuclear track detectors (PNTD). In correction of efficiency change of TDMS, it was assumed that reduction of efficiency is predominantly attributed to HZE particles with energy greater than 100 MeV amu-1. A conservative calibration curve was chosen for LET determination from PNTD track-formation sensitivities. The organ and tissue absorbed doses during the mission ranged from 1.7 to 2.7 mGy, varying by a factor of 1.6. The dose equivalent ranged from 3.4 to 5.2 mSv with a variation factor of 1.5 on the basis of the Q-LET relationship in the 1990 recommendation of the ICRP. The effective quality factor (Qe) varied from 1.7 to 2.4. The dose equivalents at several radiation-sensitive organs, such as the stomach, lung, gonad and breast, were not significantly different from the skin dose equivalent (Hskin). The effective dose equivalent was evaluated as 4.1 mSv; this value was about 90 % of the Hskin.

Publications:
1) Yasuda, H., Badhwar, G.D., Komiyama, T. and Fujitaka, K.: Radiat. Res. 154, 705-713, 2000.
2) Yasuda, H. and Fujitaka, K.: Radiat. Prot. Dosim. 87, 115-120, 2000.
3) Yasuda, H. and Fujitaka, K.: Radiat. Meas. 32, 355-360, 2000.


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