Effective dose equivalent on the ninth Shuttle--Mir mission (STS-91)

Area of Science:

• Space radiation dosimetry
• Astrobiology and space medicine
• Radiation physics

Background:

• Spaceflight exposes astronauts to unique radiation environments, including galactic cosmic rays and solar particle events.
• Accurate measurement of organ and effective doses is crucial for assessing health risks to astronauts.
• Previous dosimetry on space missions often relied on limited measurement points and detector types.

Purpose of the Study:

• To measure organ and tissue doses and effective dose equivalent during the Shuttle-Mir Mission (STS-91).
• To assess the spatial variation of radiation dose within a human phantom in low-Earth orbit.
• To evaluate the effective quality factor and compare organ doses to skin dose.

Main Methods:

• Utilized a life-size human phantom instrumented with 59 thermoluminescent dosimeters (Mg(2)SiO(4):Tb, TDMS) and plastic nuclear track detectors (PNTD).
• Corrected TDMS efficiency reductions attributed to high-energy HZE particles (>100 MeV nucleon(-1)).
• Determined linear energy transfer (LET) from PNTD track-formation sensitivities using a conservative calibration curve.

Main Results:

• Organ and tissue absorbed doses ranged from 1.7 to 2.7 mGy (factor of 1.6 variation).
• Dose equivalents ranged from 3.4 to 5.2 mSv (factor of 1.5 variation), based on ICRP 1990 recommendations.
• Effective dose equivalent was calculated as 4.1 mSv, approximately 90% of the skin dose equivalent (H(skin)).

Conclusions:

• The effective dose equivalent during the STS-91 mission was 4.1 mSv, with significant spatial variation in organ doses.
• Dose equivalents to radiation-sensitive organs (stomach, lung, gonad, breast) were comparable to skin dose.
• These findings highlight the importance of comprehensive dosimetry for astronaut radiation protection in low-Earth orbit.