Radiation environment in high-altitude Antarctic plateau: Recent measurements and model studies.

Polar regions are the most exposed to secondary particles and radiation produced by primary cosmic rays in the atmosphere, because naturally they are with marginal geomagnetic shielding. In addition, the secondary particle flux contributing to the complex radiation field is enhanced at high-mountain altitudes compared to sea level because of the reduced atmospheric attenuation. At present, there are very few systematic experimental measurements of environmental dose at high southern latitudes, specifically at high-altitude region. Here, we report a campaign of measurements with different devices, that is passive and Liulin-type dosimeters, of the radiation background at high-mountain Antarctic station Vostok (3488 m above sea level, 78° 27' S; 106° 50' E). We compare the measurements with a Monte Carlo-based model for the propagation of the cosmic rays through the atmosphere and assessment of the radiation field in the atmosphere. We employed the model to estimate the radiation dose at Vostok station during the ground-level enhancement at 28 October 2021. As in previous studies by other teams, we show that the annual dose equivalent at high-altitude Antarctic facilities can significantly exceed the limit of 1 mSv established for the general population by the ICRP.

Ray-tracing simulation of the radiation dose distribution on the surface of the spherical phantom of the MATROSHKA-R experiment onboard the ISS.

Space radiation is one of the main concerns for human space flights. The prediction of the radiation dose for the actual spacecraft geometry is very important for the planning of long-duration missions. We present a numerical method for the fast calculation of the radiation dose rate during a space flight. We demonstrate its application for dose calculations during the first and the second sessions of the MATROSHKA-R space experiment with a spherical tissue-equivalent phantom. The main advantage of the method is the short simulation time, so it can be applied for urgent radiation dose calculations for low-Earth orbit space missions. The method uses depth-dose curve and shield-and-composition distribution functions to calculate a radiation dose at the point of interest. The spacecraft geometry is processed into a shield-and-composition distribution function using a ray-tracing method. Depth-dose curves are calculated using the GEANT4 Monte-Carlo code (version 10.00.P02) for a double-layer aluminum-water shielding. Aluminum-water shielding is a good approximation of the real geometry, as water is a good equivalent for biological tissues, and aluminum is the major material of spacecraft bodies. The method is applied to model the dose distribution on the surface of the spherical phantom in the MATROSHKA-R space experiment. The experiment has been carried out onboard the ISS from 2004 to the present. The absorbed dose was determined in 32 points on the phantom's surface. We find a good agreement between the data obtained in the experiment and our calculation results. The simulation method is thus applicable for future radiation dose predictions for low-Earth orbit missions and experiments.

MEASUREMENT OF DIFFERENT COMPONENTS OF SECONDARY RADIATION ONBOARD INTERNATIONAL SPACE STATION BY MEANS OF PASSIVE DETECTORS.

The evaluation of different components of secondary radiation (charged fragments and neutrons) onboard ISS is described. Solid-state nuclear track detectors CR-39™ were applied for the measurements of short-range nuclear fragments, while the measurements of neutrons were carried out by means of thermo-luminescent dosimeters with various concentrations of 6Li and 7Li. The flux of charged secondaries and the gamma-equivalent neutron dose are presented in function of the low-LET dose in various modules of the Russian segment of ISS.

CONTRIBUTION OF DIFFERENT PARTICLES MEASURED WITH TRACK ETCHED DETECTORS ONBOARD ISS.

Cosmic radiation consists of primary high-energy galactic and solar particles. When passing through spacecraft walls and astronauts' bodies, the spectrum becomes even more complex due to generating of secondary particles through fragmentation and nuclear interactions. Total radiation exposure is contributed by both these components. With an advantage, space research uses track etched detectors from the group of passive detectors visualizing the tracks of particles, in this case by etching. The detectors can discriminate between various components of cosmic radiation. A method is introduced for the separation of the different types of particles according to their range using track etched detectors. The method is demonstrated using detectors placed in Russian segment of the International Space Station in 2009. It is shown that the primary high-energy heavy ions with long range contribute up to 56% of the absorbed dose and up to 50% to the dose equivalent.

[SUBSTANTIATION OF DOSE LIMITS FOR A NEW NORMATIVE DOCUMENT ON RADIATION SAFETY OF LONG-DURATION SPACE MISSIONS AT ORBIT ALTITUDES OF UP TO 500 KM].

Review of the data of experimental radiobiology and epidemiological follow-up of large groups of people subjected to radiation exposures on Earth has been undertaken to substantiate dose limits for critical organs of cosmonauts in order to ensure good performance and vitality while on long-duration orbital missions. The career dose limits for cosmonauts and astronauts established earlier in the USSR and USA amounted to nothing more but banning the risk of cancer death increase to 3%. To apply more rigorous criteria of delayed radiation risks, the Russian limits for cosmonauts were revised to substantiate a 4-fold reduction of the average tissue equivalent dose maximum to 1 Sv. The total of cancer and non-cancer radiation risks over lifetime and probable reduction of mean life expectancy (MLE) were calculated using the model of radiation-induced mortality for mammals and taken as the main damage to health. The established dose limit is equal to the career dose for nuclear industry personnel set forth by Russian standard document NRB 99/2009. For better agreement of admissible threshold doses to critical human organs (bone marrow, lens and skin) in the revised radiation limits for long-duration space missions and radiation safety limits on Earth, reduction of dose limits for the critical organs were substantiated additionally; these limits comply with those for planned over-exposure on Earth in document NRB 99/2009.

[CALCULATION OF RADIATION LOADS ON THE ANTHROPOMORPHIC PHANTOM ONBOARD THE SPACE STATION IN THE CASE OF ADDITIONAL SHIELDING].

The paper presents the results of calculating doses from space ionizing radiation for a modeled orbital station cabin outfitted with an additional shield aimed to reduce radiation loads on cosmonaut. The shield is a layer with the mass thickness of -6 g/cm2 (mean density = 0.62 g/cm3) that covers the outer cabin wall and consists of wet tissues and towels used by cosmonauts for hygienic purposes. A tissue-equivalent anthropomorphic phantom imitates human body. Doses were calculated for the standard orbit of the International space station (ISS) with consideration of the longitudinal and transverse phantom orientation relative to the wall with or without the additional shield. Calculation of dose distribution in the human body improves prediction of radiation loads. The additional shield reduces radiation exposure of human critical organs by -20% depending on their depth and body spatial orientation in the ISS compartment.

Overview of the Liulin type instruments for space radiation measurement and their scientific results.

Ionizing radiation is recognized to be one of the main health concerns for humans in the space radiation environment. Estimation of space radiation effects on health requires the accurate knowledge of the accumulated absorbed dose, which depends on the global space radiation distribution, solar cycle and local shielding generated by the 3D mass distribution of the space vehicle. This paper presents an overview of the spectrometer-dosimeters of the Liulin type, which were developed in the late 1980s and have been in use since then. Two major measurement systems have been developed by our team. The first one is based on one silicon detector and is known as a Liulin-type deposited energy spectrometer (DES) (Dachev et al., 2002, 2003), while the second one is a dosimetric telescope (DT) with two or three silicon detectors. The Liulin-type instruments were calibrated using a number of radioactive sources and particle accelerators. The main results of the calibrations are presented in the paper. In the last section of the paper some of the most significant scientific results obtained in space and on aircraft, balloon and rocket flights since 1989 are presented.

[MEASUREMENT OF SPACE RADIATION DOSES AND LINEAR ENERGY TRANSFER SPECTRA INSIDE BIOLOGICAL SATELLITE BION-M1].

The paper presents the results of measuring biologically significant characteristics of space radiation (spectra of linear energy transfer (LET), absorbed and equivalent doses and averaged quality factors) inside the descend capsule of biosatellite Bion-M1 in space experiment Bioradiation. Measurements combined the use of thermoluminescent detectors DTG-4 (TDL) and solid state nuclear track detectors CR-39 (Tastrak) (SSNTD). Differential and integral LET spectra of high-LET space radiation were determined in 4 points inside spacecraft using passive detectors assembles (PDA). Total absorbed dose rates for PDA boxes No 1-4 made up 2.4 ± 0.2; 1.1 ± 0.1; 1.6 ± 0.2; 2.0 ± 0.1 mGy/d respectively, whereas total equivalent dose rates estimated based on ICRP Publication 60 recommendations made up 3.4 ± 0.2; 2.0 ± 0.1; 2.6 ± 0.2; 3.1 ± 0.1 mSv/d respectively. Values of the averaged quality factor for different PDSs were in the range between 1.4 and 1.8.

[MODIFICATION OF THE PROTON BEAM PHYSICAL PARAMETERS AND RADIOBIOLOGICAL CHARACTERISTICS BY ELEMENTS OF SPACECRAFT RADIATION PROTECTION].

The experiment was performed with outbred ICR (CD-1). female mice (SPF). The animals were irradiated by 171 MeV protons at a dose of 20 cGy. The spacecraft radiation protection elements used in the experiment were a construction of wet hygiene wipes called a "protective blind", and a glass plate imitating an ISS window. Physical obstacles on the path of 171 MeV protons increase their linear energy transfer leading to the absorbed dose elevation and strengthening of the radiobiological effect. In the experiment, two types of obstacles together raised the absorbed dose from 20 to 23.2 cGy. Chemically different materials (glass and water in the wipes) were found to exert unequal modifying effects on physical and biological parameters of the proton-irradiated mice. There was a distinct dose-dependent reduction of bone marrow cellularity within the dose range from 20 cGy to 23.2 cGy in 24 hours after exposure. No modifying effect of the radiation protection elements on spontaneous motor activity was discovered when compared with entrance protons. The group of animals protected by the glass plate exhibited normal orientative-trying reactions and weakened grip with the forelimbs. Rationalization of physical methods of spacecrew protection should be based as on knowledge in physical dosimetry (ionizing chambers, thermoluminescent, track detectors etc.), so the radiobiological criteria established in experiments with animals.

[Results of measuring neutrons doses and energy spectra inside Russian segment of the International Space Station in experiment "Matryoshka-R" using bubble detectors during the ISS-24-34 missions].

The paper presents the results of calculating the equivalent dose from and energy spectrum of neutrons in the right-hand crewquarters in module Zvezda of the ISS Russian segment. Dose measurements were made in the period between July, 2010 and November, 2012 (ISS Missions 24-34) by research equipment including the bubble dosimeter as part of experiment "Matryoshka-R". Neutron energy spectra in the crewquarters are in good agreement with what has been calculated for the ISS USOS and, earlier, for the MIR orbital station. The neutron dose rate has been found to amount to 196 +/- 23 microSv/d on Zvezda panel-443 (crewquarters) and 179 +/- 16 microSv/d on the "Shielding shutter" surface in the crewquarters.

[Calculation of radiation loads in a space station compartment with a secondary shielding].

Doses from space ionizing radiation were estimated using a model of ISS cosmonaut's quarters (CQ) outfitted with secondary shielding ("Protective shutter" (PS) as part of experiment MATRYOSHKA-R). Protective shutter is a "blanket" of water-containing material with mass thickness of - 6 g/cm2 covering the CQ exterior wall. Calculation was performed specifically for locations of experimental dosimetry assemblies. Agreement of calculations and experimental data reaching accuracy - 15% proves model applicability to estimating protective effectiveness of secondary shielding in the present-day and future space vehicles. This shielding may reduce radiation loading onto crewmembers as an equivalent dose by more than 40% within a broad range of orbit altitudes equally during the solar minimum and maximum.

[A new approach to shielding function calculation: radiation dose estimation for a phantome inside space station compartment].

The article presents a new procedure of calculating the shielding functions for irregular objects formed from a set of nonintersecting (adjacent) triangles covering completely the surface of each object. Calculated and experimentally derived distributions of space ionizing radiation doses in the spherical tissue-equivalent phantom (experiment MATRYOSHKA-R) inside the International space station were in good agreement in the mass of phantom depths with allowance for measurement error (-10%). The procedure can be applied in modeling radiation loads on cosmonauts, calculating effectiveness of secondary protection in spacecraft, and design review of radiation protection for future space exploration missions.

Monitoring on board spacecraft by means of passive detectors.

To estimate the radiation risk of astronauts during space missions, it is necessary to measure dose characteristics in various compartments of the spacecraft; this knowledge can be further used for estimating the health hazard in planned missions. This contribution presents results obtained during several missions on board the International Space Station (ISS) during 2005-09. A combination of thermoluminescent and plastic nuclear track detectors was used to measure the absorbed dose and dose equivalent. These passive detectors have several advantages, especially small dimensions, which enabled their placement at various locations in different compartments inside the ISS or inside the phantom. Variation of dosimetric quantities with the phase of the solar cycle and the position inside the ISS is discussed.

[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.

[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.

[Dose distribution in the depth of the tissue-equivalent ball phantom modeling location of human body critical organs inside the compartments of the International space station].

Goal of the investigation is to study and to analyze radiation dose distribution in cosmonaut's body during long-term mission aboard the International space station (ISS). The established patterns of dose distribution under different conditions of the experiment allow simplify evaluation of dose accumulation by spacecrew. Dose from ionizing space radiation was determined with the help of thermoluminescent dosimeters mounted in conditional depths of critical organs in human body modeled in a dosimetric device, i.e.--a ball-like tissue-equivalent phantom designed and manufactured in Russia for international space experiment Matreshka-R. The article reports experimental data disclosing the character and levels of exposure to ionizing radiation inside the Service module crew quarters during ISS missions 8 and 9 (425 days, 2004-2005) and the docking compartment (SO1) during ISS missions 15 and 16 (285 days, 2007-2008).

[Radiation protective quality of spacesuit "Orlan-M" during extravehicular activities on the International Space Station].

Sampling irradiation of spacesuit "Orlan-M" allowed construction of a simulation model of the spacesuit shielding function for critical body organs. The critical organs self-shielding model is a Russian standard anthropomorphic phantom. Radiation protective quality of the spacesuit was assessed by calculating the dose attenuation rates for several critical body organs of an ISS crewmember implementing EVA. These calculations are intended for more accurate assessment of radiation risk to the ISS crews donning "Orlan-M" in near-Earth orbits.

[Method of calculating self-shielding of the human critical organs in the anthropomorphic phantom]. / Metodika rascheta samoékranirovannosti kriticheskikh organov tela cheloveka v antropomorfnom fantome.

Proposed is a procedure of calculating the self-screening function of a point on the human body model. The procedure has been developed for the anthropomorphic phantom approved in Russian standard GOST 25645.203-83. The procedure allows extrapolation of the self-shielding calculations to a different body model and a partially protected human body (intra- and extravehicular spacesuit, etc). Results can be useful in precise determination of radiation risks with consideration of the organs self-shielding factor.

[Problems of radiation safety of a Martian expedition crew]. / Problemy radiatsionnoi bezopasnosti ékipazha marsianskoi ékspeditsii.

Analysis of the radiation conditions during a piloted expedition to Mars made it evident that the radiation safety system will be one of the most critical components of life support aboard the future Martian vehicle. The concept and main functions of the system have been considered. The authors give their vision of the radiation monitoring system based on the present-day radiation safety postulates, comparison and contrasting methods and equipment applied for the purpose in current orbital and projected interplanetary flights.

Analysis of the Cyclotron Facility calibration and aircraft dosimetry results from the LIULIN-3M instrument.

The LIULIN-3M instrument is a further development of the LIULIN dosimeter-radiometer, used on the MIR spacestation during the 1988-1994 time period. The LIULIN-3M is designed for continuous monitoring of the radiation environment during the BION-12 satellite flight in 1999. A semiconductor detector with 1 mm thickness and cm2 area is contained in the instrument. Pulse high analysis technique is used to determine the energy losses in the detector. The final data from the instrument are the flux and the dose rate for the exposure time and 256 channels of absorbed dose spectra based on the assumption that the particle flux is normal to the detector. The LIULIN-3M instrument was calibrated by proton fluxes with different energies at the Indiana University Cyclotron Facility in June 1997 and had been used for radiation measurements during commercial aircraft flights. The calibration procedure and some flight results are presented in this paper.