This experiment attempted to expand the knowledge of environmental radiation at the 51.6 degree orbit, the location of the Mir station and future location of the International Space Station. Information on the shielding effects of the station and different methods of radiation dosimetry was also gathered. The data and associated analysis contributed to the establishment of a reliable database for the radiation environment in space.
Two types of spectra were measured and compared: linear energy transfer (LET) and absorbed dose. The measurements for both spectra occurred inside six area passive dosimeters (APDs) that were flown to Mir via Shuttle mission STS-76 and placed at six different locations on Mir. LET spectra was measured using CR-39 PNTDs that were placed on the APDs. The CR-39 plates were etched with a NaOH solution and read out on an image digitizer system and analyzed. The absorbed spectra was measured using thermoluminescent detectors (TLDs) attached to the APDs. The flight data was compared with data read from background and calibration TLDs.
By using identical APDs in the exact locations on Mir, changes in radiation levels over time were recorded and analyzed. The measured dose rates in the APDs ranged from 268 to 422 mGy/d, yielding an average of 324 mGy/d. The differences in the high and low values were most likely caused by shielding differences due to the individual APD placements on Mir. Also, secondary target fragments, generated by inelastic scattering of protons and alpha particles within the detector medium, contributed to the spread of values. The dose and dose equivalent rates were used to calculate the effective quality factor, which was determined to be about 9 for LETs 25 keV/mm. This value shows the significance of short-range high LET target fragments to dose equivalent. The shielding data is currently being used to model the APD measurements made in the Mir Core.