RADIATION-DOSIMETRY MEASUREMENTS WITH REAL-TIME RADIATION MONITORING DEVICE (RRMD)-II IN SPACE-SHUTTLE STS-79

The real-time measurement of radiation environment was made with an im proved real-time radiation monitoring device (RRMD)-II onboard Space S huttle STS-79 (S/MM#4: 4th Shuttle MIR Mission, at an inclination angl e of 51.6 degrees and an altitude of 250-400km) for 199 h during 17-25 September, 1996. The observation of the detector covered the linear e nergy transfer (LET) range of 3.5-6000 keV/mu m. The Shuttle orbital p rofile in this mission was equivalent to that of the currently planned Space Station, and provided an opportunity to investigate variations in count rate and dose equivalent rate depending on altitude, longitud e: and latitude in detail. Particle count rate and dose equivalent rat e were mapped geographically during the mission. Based on the map of c ount rate, an analysis was made by dividing whole region into three re gions: South Atlantic Anomaly (SAA) region, high latitude region and o ther regions. The averaged absorbed dose rate during the mission was 3 9.3 mu Gy/day for a LET range of 3.5-6000 keV/mu m. The corresponding average dose equivalent rates during the mission are estimated to be 2 93 mu Sv/day with quality actors from International Commission on Radi ological Protection (ICRP)-Pub. 60 and 270 mu Sv/day with quality fact ors from ICRP-Pub. 26. The effective quality factors for ICRP-Pub. 60 and 26 are 7.45 and 6.88, respectively. From the present data for part icles of LET > 3.5keV/mu m, we conclude that the average dose equivale nt rate is dominated by the contribution of galactic cosmic ray (GCR) particles. The dose-detector depth dependence was also investigated.