The Liulin-5 experiment is a part of the international project MATROSHKA-R on the Russian segment of the ISS, which uses a tissue-equivalent spherical phantom equipped with a set of radiation detectors. The objective of the MATROSHKA-R project is to provide depth dose distribution of the radiation field inside the sphere in order to get more information on the distribution of dose in a human body. Liulin-5 is a charged particle telescope using three silicon detectors. It measures time resolved energy deposition spectra, linear energy transfer (LET) spectra, particle flux, and absorbed doses of electrons, protons and heavy ions, simultaneously at three depths along the radius of the phantom. Measurements during the minimum of the solar activity in cycle 23 show that the average absorbed daily doses at 40 mm depth in the phantom are between 180 μGy/day and 220 μGy/day. The absorbed doses at 165 mm depth in the phantom decrease by a factor of 1.6–1.8 compared to the doses at 40 mm depth due to the self-shielding of the phantom from trapped protons. The average dose equivalent at 40 mm depth is 590 ± 32 μSV/day and the galactic cosmic rays (GCR) contribute at least 70% of the total dose equivalent at that depth. Shown is that due to the South Atlantic Anomaly (SAA) trapped protons asymmetry and the direction of Liulin-5 lowest shielding zone the dose rates on ascending and descending nodes in SAA are different. The data obtained are compared to data from other radiation detectors on ISS.
Research Containing: Tissue-equivalent
Investigation of dose and flux dynamics in the Liulin-5 dosimeter of the tissue-equivalent phantom onboard the Russian segment of the international space station
Described is the Liulin-5 active dosimetric telescope designed for measurement of the space radiation dose depth-distribution in a human phantom on the Russian Segment of the International Space Station (ISS). The Liulin-5 experiment is a part of the international project MATROSHKA-R on ISS. The MATROSHKA-R project is aimed to study the depth- dose distribution at the sites of critical organs of the human body, using models of human body-anthropomorphic ant spherical tissue-equivalent phantoms. The aim of Liulin-5 experiment is a long term (4–5 years) investigation of the radiation environment dynamics inside the spherical tissue-equivalent phantom, mounted in different compartments. Energy deposition spectra, linear energy transfer spectra, and flux and dose rates for charged particles will be measured simultaneously with near real time resolution at different depths of the phantom by means of three silicon detectors. Data obtained together with data from other active and passive dosimeters will be used to estimate the radiation risk to the crewmembers, which verify the models of radiation environment in low Earth orbit. Presented are the test results of the prototype unit. Liulin-5 will be flown on the ISS in the year 2003.
Study of radiation conditions onboard the International space station by means of the Liulin-5 dosimeter
For estimating radiation risk in space flights it is necessary to determine radiation dose obtained by critical organs of a human body. For this purpose the experiments with human body models are carried out onboard spacecraft. These models represent phantoms equipped with passive and active radiation detectors which measure dose distributions at places of location of critical organs. The dosimetric Liulin-5 telescope is manufactured with using three silicon detectors for studying radiation conditions in the spherical tissue-equivalent phantom on the Russian segment of the International space station (ISS). The purpose of the experiment with Liulin-5 instrument is to study dynamics of the dose rate and particle flux in the phantom, as well as variations of radiation conditions on the ISS over long time intervals depending on a phase of the solar activity cycle, orbital parameters, and presence of solar energetic particles. The Liulin-5 dosimeter measures simultaneously the dose rate and fluxes of charged particles at three depths in the radial channel of the phantom, as well as the linear energy transfer. The paper presents the results of measurements of dose rate and particle fluxes caused by various radiation field components on the ISS during the period from June 2007 till December 2009.
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.
Radiation measurements of surface and deep organ doses were performed aboard the International Space Station, for the period of January 2006 to April 2007, using a MOSFET dosimetry system combined with the Matroshka-R spherical phantom. The averaged internal and surface dose rates are found to be 0.19 and 0.29 mGy d(-1), respectively. The levels of radiation dose to blood-forming organs (BFO) and to surface organs are compared with recommended safe limits. The maximum measured BFO dose has an average dose rate of 0.23 mGy d(-1) (84 mGy y(-1)), corresponding to 44 % of the recommended annual limit of 0.5 Sv, for a space radiation quality factor of 2.6. The annual surface dose is found to be higher at 126 mGy, corresponding to 16 % of the eye dose limit and to 11 % of the skin dose limit. Doses calculated using the Spenvis software showed deviations of up to 37 % from measurements.
Results of measuring neutron dose inside the Russian segment of the International Space Station using bubble detectors in experiment Matreshka-R
Distribution of neutron equivalent dose both inside and outside the spherical phantom (experiment Matryeshka-R) was determined with the help of dedicated research equipment "Bubble-dosimeter". Equipment is built up from an automatic bubbles counter and 8 bubble detectors of neutrons with energy ranging from approximately 200 keV to 15 MeV. Measurements inside the ISS were made in several 7-day sessions in the period from April 2006 till October 2007 (ISS increments 13-15). According to the bubble detectors on the outside of the phantom, ambient neutron dose H*(10) was equal to 0.1 mSv/d or approximately 20% of the dose from charged particles inside the ISS. In the tissue-equivalent phantom, neutron dose was 1.2 +/- 0.2 times less as compared with the phantom surface which characterized the degree of dose attenuation in cosmonaut's body.
The MATROSHKA Experiment: Results and Comparison from Extravehicular Activity (MTR-1) and Intravehicular Activity (MTR-2A/2B) Exposure
Astronauts working and living in space are exposed to considerably higher doses and different qualities of ionizing radiation than people on Earth. The multilateral MATROSHKA (MTR) experiment, coordinated by the German Aerospace Center, represents the most comprehensive effort to date in radiation protection dosimetry in space using an anthropomorphic upper-torso phantom used for radiotherapy treatment planning. The anthropomorphic upper-torso phantom maps the radiation distribution as a simulated human body installed outside (MTR-1) and inside different compartments (MTR-2A: Pirs; MTR-2B: Zvezda) of the Russian Segment of the International Space Station. Thermoluminescence dosimeters arranged in a 2.54 cm orthogonal grid, at the site of vital organs and on the surface of the phantom allow for visualization of the absorbed dose distribution with superior spatial resolution. These results should help improve the estimation of radiation risks for long-term human space exploration and support benchmarking of radiation transport codes.