This paper presents results from dosimetric measurements made aboard the Mir space station and the International Space Station (ISS) using the Pille portable thermoluminescent dosemeter (TLD) system. This paper includes the dosimetry mapping and automatic readout (trapped and untrapped components) results from Mir and ISS. The mean dose rate in 2001–2003 was 7 μGy h−1. Using the hourly measuring period in automatic mode, doses from both galactic (independent of South Atlantic Anomaly—SAA) and SAA components were determined during Euromir'95 experiment. The mean total dose rate was 12.5 μGy h−1, while the SAA contribution was 6.2 μGy h−1. A similar measurement was performed on ISS in 2001 and in 2003. Both the manual and automatic measurements show a significant decrease in dose rate in 2001 in comparison to 1995–1997 due to the change in solar activity. For determination of the high linear energy transfer contribution from the radiation field during the ISS mapping experiment, three CR-39 plastic nuclear track detectors (PNTDs) were co-located with each TL detector. Analysis of the combined TLD and PNTD measurements showed a typical mean TLD efficiency of 84%, a dose contribution <10 keV μm−1 of 17%, and an average quality factor of 1.95.
Research Containing: Dose equivalents
Radiation in low Earth orbit (LEO) is mainly from Galactic Cosmic Rays (GCR), solar energetic particles and particles in South Atlantic Anomaly (SAA). These particles’ radiation impact to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field and the influence of radiation on astronauts. At present, the best active dosimeters used for all LET are the tissue equivalent proportional counter (TEPC) and silicon detectors; the best passive dosimeters are thermoluminescence dosimeters (TLDs) or optically stimulated luminescence dosimeters (OSLDs) for low LET and CR-39 plastic nuclear track detectors (PNTDs) for high LET. TEPC, CR-39 PNTDs, TLDs and OSLDs were used to investigate the radiation for space mission Expedition 12 (ISS-11S) in LEO. LET spectra and radiation quantities (fluence, absorbed dose, dose equivalent and quality factor) were measured for the mission with these different dosimeters. This paper introduces the operation principles for these dosimeters, describes the method to combine the results measured by CR-39 PNTDs and TLDs/OSLDs, presents the experimental LET spectra and the radiation quantities.
Results of neutron dose measurements inside and outside International Space Station are presented. Measurements outside module «Zvezda» were conducted with Board Neutron Telescope (BTN) from 2007 to 2010. The telescope consists of three 3He counters and organic scintillator crystal (stylbene). BTN performs to work within the range of 0.1eV –10MeV. Measurements inside module «Zvezda» were conducted with so called Bubble Detectors in the same energy interval. Comparison of results is presented.
Cosmic ray detection on the ISS by a 3 axes track etch detector stack and the complementary calibration studies
The complex radiation field inside the International Space Station (ISS) as well as the dose received by its crew was studied for several years in the BRADOS ( 1 – 5 ) projects organized by the Institute for Biomedical Problems (IBMP, Moscow) with the participation of different laboratories. The results of the measurements performed during the BRADOS-5 project by a 3 axes solid state nuclear track detector (SSNTD) stack as LET spectra and dose values are presented. According to the results, no remarkable directional dependence could be observed in the radiation field. The averaged absorbed dose rate and dose equivalent rate values above ∼ 12 keV μ m – 1 were 27.0 ± 1.6 μ Gy d – 1 and 211.4 ± 14.4 μ Sv d – 1 , respectively, resulting in an averaged quality factor of 7.9 ± 0.1 .
A PAssive Dosimeter for Life-science Experiments in Space (PADLES) has been developed for measuring total absorbed dose and dose equivalents in the radiation environments of the International Space Station (ISS) where the Linear Energy Transfer (LET) of radiation ranges from 0.2 (ionization minimum) to 103 keVμm−1 or more. PADLES consists of two types of passive and integrating radiation detectors: MSO-S (Mg2SiO4:Tb) ThermoLuminescence Dosimeters (TLDs) and antioxidant-doped CR-39 plastic nuclear track detectors. In this paper, we first describe a method to obtain a water-equivalent absorbed dose by combining data from these two types of detector. In order to increase the reliability of PADLES for ISS space radiation dosimetry, we investigated the following characteristics of MSO-S TLDs: calibration of our ThermoLuminescence (TL) readout system for high-energy protons and gamma rays from 60Co and 137Cs sources; dose responses for high-energy heavy ions (He, C, Si, Ar, Fe); response variation of different manufacture batches; directional response for the high-energy protons; the initial variations and long-term fading effects of the TL response for high-energy protons and heavy ions at temperatures from −80 °C to 60 °C; and LET response.
Astronaut's organ doses inferred from measurements in a human phantom outside the international space station
Space radiation hazards are recognized as a key concern for human space flight. For long-term interplanetary missions, they constitute a potentially limiting factor since current protection limits for low-Earth orbit missions may be approached or even exceeded. In such a situation, an accurate risk assessment requires knowledge of equivalent doses in critical radiosensitive organs rather than only skin doses or ambient doses from area monitoring. To achieve this, the MATROSHKA experiment uses a human phantom torso equipped with dedicated detector systems. We measured for the first time the doses from the diverse components of ionizing space radiation at the surface and at different locations inside the phantom positioned outside the International Space Station, thereby simulating an extravehicular activity of an astronaut. The relationships between the skin and organ absorbed doses obtained in such an exposure show a steep gradient between the doses in the uppermost layer of the skin and the deep organs with a ratio close to 20. This decrease due to the body self-shielding and a concomitant increase of the radiation quality factor by 1.7 highlight the complexities of an adequate dosimetry of space radiation. The depth-dose distributions established by MATROSHKA serve as benchmarks for space radiation models and radiation transport calculations that are needed for mission planning.
Area radiation monitoring on ISS Increments 17 to 22 using PADLES in the Japanese Experiment Module Kibo
The measurement of radiation environmental parameters in space is essential to support radiation risk assessments for astronauts and establish a benchmark for space radiation models for present and future human space activities. The Japan Aerospace Exploration Agency (JAXA) is performing a continuous area radiation monitoring experiment using the “PAssive Dosimeters for Lifescience Experiments in Space” (PADLES) system inside the Japanese Experiment Module Kibo on board the International Space Station (ISS). The PADLES dosimeter consists of thermoluminescent dosimeters (TLDs) and CR-39 plastic nuclear track detectors (PNTDs). JAXA has run the Area PADLES experiment since the Kibo module was attached to the ISS in June 2008, using 17 dosimeters in fixed locations on the Pressurized Module (PM) and the Experiment Logistics Module-Pressurized Section (ELM-PS) of Kibo, which are replaced every 6 months or every Increment, respectively. For three monitoring periods, known as Area PADLES experiment series #1 to #3, of 301, 180, and 232 days in June 2008 to April 2010 over ISS Increments 17 to 22, the average absorbed dose (dose equivalent) rates of 12 positions in the PM of Kibo were 319 ± 30 μGy/day (618 ± 102 μSv/day), 276 ± 30 μGy/day (608 ± 94 μSv/day), and 293 ± 33 μGy/day (588 ± 84 μSv/day), respectively. The radiation measurement in the ELM-PS was conducted in only Area PADLES experiment series #3 from August 2009 to April 2010 (232 days) over ISS Increments 21 to 22, the average absorbed dose (dose equivalent) rates of 5 positions was 297 ± 28 μGy/day (661 ± 65 μSv/day). The directional dependence of the radiation field was also investigated by installing PADLES dosimeters located in the zenith of ELM-PS of Kibo.
Variation of absorbed doses onboard of ISS Russian Service Module as measured with passive detectors
Cosmic radiation represents possible risk for the astronauts. For estimation of the radiation onboard the spacecraft in space flights, it is necessary to obtain the data on dose distribution in real space flight conditions. This contribution deals with the study of absorbed dose and dose equivalent due to space radiation in different compartments of the International Space Station (ISS) using passive detectors. Luminescent detectors (LD) and CR-39 plastic nuclear track detectors (PNTD) were exposed onboard of Russian Service Module on ISS from August 2004 to October 2005 (425 days); they were placed at SPD boxes and positioned at 6 various locations inside the Russian Service Module. LD were used to measure absorbed doses, particularly from low-LET particles and photons, PNTDs were used to measure the spectra of linear energy transfer (LET), absorbed dose, and dose equivalents from particles with LET∞H2O >5 keV/μm. Results from both types of detectors (LD and PNTD) were then combined together to obtain total values of absorbed doses and dose equivalents. Distribution of absorbed doses and dose equivalents measured with passive detectors, as well as LET spectra of registered particle fluxes, are presented as the function of position of SPD boxes (shielding thickness). Also the influence of position of detectors inside the SPD boxes (top and bottom wall) will be discussed. The dose characteristics depend on the location inside the Service Module; their variation has been observed to be up to factor of almost 2.
Space radiation doses in the anthropomorphous phantom in space experiment "Matryeshka-R" and spacesuit "Orlan-M" during extravehicular activity
Russian space experiment "Matryeshka-R" was conducted in 2004-2005 to study dose distribution in the body of anthropomorphous phantom inserted in a spacesuit imitating container mounted on outer surface of the ISS Service module (experiment "Matryeshka"). The objective was to compare doses inside the phantom in the container to human body donned in spacesuit "Orlan-M" during extravehicular activity (EVA). The shielding function was calculated using the geometric model, specification of the phantom shielded by the container, "Orlan-M" description, and results of ground-based estimation of shielding effectiveness by gamma-raying. Doses were calculated from the dose attenuation curves obtained for galactic cosmic rays, and the AE-8/AP-8 models of electron and proton flows in Earth's radiation belt. Calculated ratios of equivalent doses in representative points of the body critical organs to analogous doses in phantom "Matryeshka" H(ORLAN-M)/H(Matryeshka) for identical radiation conditions vary with organs and solar activity in the range from 0.1 to 1.8 with organs and solar activity. These observations should be taken into account when applying Matryeshka data to the EVA conditions.
The dose values in body's critical organs are necessary for estimating the effective dose. The tissue-equivalent phantom is used for such assessment as a rule. The spherical phantom is best fit for this goal. Therefore, the method developed on the basis of such phantom application becomes a good mean of effective dose estimating onboard the International Space Station. The main problems connected with developing a method of assessing an effective dose in the human's body organs with usage of a spherical phantom are presented in the paper. Proposed method can be used for monitoring the daily effective dose of crewmembers exposure for undisturbed radiation conditions of the flight.