Modeling of the radiation exposure during the flight of the second Bulgarian cosmonaut on board the Mir Space Station.

An experiment involving active detection of space radiation was carried out in the Space Research Institute (SRI) of Bulgarian Academy of Sciences, in preparation of the flight of the second Bulgarian cosmonaut. The radiations that would be encountered on the flight were modelled including solar and galactic cosmic rays and the particle radiation in the Earth's radiation belts. The dose rate was calculated for these different radiations behind the shielding of the space station. The variations in dose rates over the period of the flight were calculated and compared with measurements made during the orbit of the Mir Space Station. The calculated and measured dose rates agreed within 15-35%.     

Solar cosmic rays as a specific source of radiation risk during piloted space flight.

Solar cosmic rays present one of several radiation sources that are unique to space flight. Under ground conditions the exposure to individuals has a controlled form and radiation risk occurs as stochastic radiobiological effects. Existence of solar cosmic rays in space leads to a stochastic mode of radiation environment as a result of which any radiobiological consequences of exposure to solar cosmic rays during the flight will be probabilistic values. In this case, the hazard of deterministic effects should also be expressed in radiation risk values. The main deterministic effect under space conditions is radiation sickness. The best dosimetric functional for its analysis is the blood forming organs dose equivalent but not an effective dose. In addition, the repair processes in red bone marrow affect strongly on the manifestation of this pathology and they must be taken into account for radiation risk assessment. A method for taking into account the mentioned above peculiarities for the solar cosmic rays radiation risk assessment during the interplanetary flights is given in the report. It is shown that radiation risk of deterministic effects defined, as the death probability caused by radiation sickness due to acute solar cosmic rays exposure, can be comparable to risk of stochastic effects. Its value decreases strongly because of the fractional mode of exposure during the orbital movement of the spacecraft. On the contrary, during the interplanetary flight, radiation risk of deterministic effects increases significantly because of the residual component of the blood forming organs dose from previous solar proton events. The noted quality of radiation responses must be taken into account for estimating radiation hazard in space.     

Radiation factors in space and a system for their monitoring.

The radiation environment is of special concern when the spaceship flies in deep space. The annual fluence of the galactic cosmic rays is approximately 10(8) cm-2 and the absorbed dose of the solar cosmic rays can reach 10 Gy per event behind the shielding thickness of 3-5 g cm-2 Al. For the radiation environment monitoring it is planned to place a measuring complex on the space probes "Mars" and "Spectr" flying outside the magnetosphere. This complex is to measure: cosmic rays composition, particle flux, dose equivalent, energy and LET spectra, solar X-rays spectrum. On line data transmission by the space probes permits to obtain the radiation environment data in space.     

Radiation exposures during space flight and their measurement.

The paper reviews radiation exposures recorded during space flights of the US and USSR. Most of the data are from manned missions and include discussion of absorbed dose and dose rates as a function of parameters such as altitude, inclination, spacecraft type and shielding. Preliminary data exist on the neutron and HZE-particle component, as well as the LET spectra. For low Earth-orbit missions, the dose encountered is strongly altitude-dependent, with a weaker dependence upon inclination. The doses range from about 6 millirad per day for the Space Transportation System No. 3 flight to about 90 mrad per day for Skylab. The effective quality factor (QF) for the near-Earth orbits and free space has been estimated to be about 1.5 and about 5.5 respectively. Complete shielding from the galactic cosmic rays does not appear practical because of spacecraft weight limitations.     

Real-time GLE alert in the ANMODAP Center for December 13, 2006

Within the last years, a real-time system to monitor high energy cosmic rays for space weather use has been operated at Athens cosmic ray station. Neutron monitors and satellite high resolution data in real time are used, making it possible to observe cosmic rays in dual energy range observations. In large solar energetic particle (SEP) events, ground level enhancement (GLE) can provide the earliest alert for the onset of the SEP event. This system watches for count rate increases recorded in real time by 23 neutron monitors, which triggers an alarm if a ground level enhancement (GLE) of cosmic ray intensity is detected.     

Radiation risk during long-term spaceflight.

Cosmonauts' exposure to cosmic rays during long-term spaceflight can cause unfavorable effects in health and risk for the crew members' lives. All unfavorable effects induced by exposure should be taken into consideration for the risk estimation. They should include both the acute deterministic effects and delayed effects called stochastic. On the ground the limitation of unfavorable consequences of acute exposure is achieved by means of establishing dose limits. But in space applications this approach can't be acceptable. Establishing a fixed dose limit is adequate to introducing indefinite reserve coefficient and therefore ineffective usage of spacecraft resource. The method of radiation risk calculation caused by acute and delayed effects of cosmonauts' exposure is discussed and substantiated in the report. Peculiarities of the impact of permanent radiation sources (galactic cosmic rays and trapped radiation) and the variable one (solar cosmic rays) are taken into consideration.     

Formation of bioorganic compounds in planetary atmospheres by cosmic radiation.

Simulated planetary atmospheres (mixtures of simple gases) were irradiated with high energy particles to simulate an action of cosmic rays. When a mixture of carbon monoxide, nitrogen and water was irradiated with 2.8-40 MeV protons, a wide variety of bioorganic compounds including amino acids, imidazole, and uracil were identified in the products. The amount of amino acids was proportional to the energy deposit to the system. Various kinds of simulated planetary atmospheres, such as "Titan type" and "Jovian type", were also irradiated with high energy protons, and gave amino acids in the hydrolyzed products. Since cosmic rays are a universal energy source in space, it was suggested that formation of bioorganic compounds in planetary atmospheres is inevitable in the course of cosmic evolution.     

Dosimetry during the first IBIS facility flight.

The dosimetry of cosmic rays was performed during the first experimental flight of the IBIS facility. Different thermoluminescent detectors (TLD) have been used to measure the contribution of the low linear energy transfer component (LET < 10 keV/micrometer) and plastic nuclear track detectors (PNTD) for the high linear energy tranfer (LET) component. Several parameters of tracks have been measured to determine the LET spectra of primary and secondary charged particles. The total absorbed dose rate (TLD+PNTD) during the flight was 0.23 mGy/day and the dose equivalent rate using the ICRP 60 was 0.52 mSv/day. The corresponding mean quality factor was 2.4. These results are in agreement with those obtained aboard the MIR station with a tissue equivalent proportional counter.     

The atmospheric radiation response to solar-particle-events.

High-energy solar particles, produced in association with solar flares and coronal mass ejections, occasionally bombard the earth's atmosphere. resulting in radiation intensities additional to the background cosmic radiation. Access of these particles to the earth's vicinity during times of geomagnetic disturbances are not adequately described by using static geomagnetic field models. These solar fluxes are also often distributed non uniformly in space, so that fluxes measured by satellites obtained at great distances from the earth and which sample large volumes of space around the earth cannot be used to predict fluxes locally at the earth's surface. We present here a method which uses the ground-level neutron monitor counting rates as adjoint sources of the flux in the atmosphere immediately above them to obtain solar-particle effective dose rates as a function of position over the earth's surface. We have applied this approach to the large September 29-30, 1989 ground-level event (designated GLE 42) to obtain the magnitude and distribution of the solar-particle effective dose rate from an atypically large event. The results of these calculations clearly show the effect of the softer particle spectra associated with solar particle events, as compared with galactic cosmic rays, results in a greater sensitivity to the geomagnetic field, and, unlike cosmic rays, the near-absence of a "knee" near 60 degrees geomagnetic latitude.     

Results on Artemia cysts, lettuce and tobacco seeds in the Biobloc 4 experiment flown aboard the Soviet Biosatellite Cosmos 1129.

Artemia cysts, lettuce and tobacco seeds were flown aboard the Cosmos 1129 for 19 days. A correlative method was used in order to determine the passage of cosmic heavy ions (HZE particles) through the biological test objects. This space flight resulted in a decrease on hatchability, nucleic acid and protein synthesis in hydrated Artemia cysts. HZE particle effects on plant cellular chromosomes are confirmed. In tobacco seeds, a stimulating effect on germination rate and a higher frequency of abnormalities were observed. Dormant biological objects are a very suitable material to study cosmic ray effects: these objects can be arranged in monolayers and sandwiched between visual track detectors in order to determine the passage of the cosmic heavy ions (HZE particles). On the other hand this method allows us to study effects of microgravity and those of the protonic component of cosmic rays in the objects not hit by the HZE articles.     

Overview on experience to date on human exposure to space radiations.

The human exposure in space depends on the three factors: the flight trajectory, its date and duration and the cyclogram of the cosmonaut's activities. In the near-Earth orbits the daily dose varies within the limits of (1.5-5.0) 10(-4) Gy day-1 and greatly increases if the altitude increases. The mean daily quality factor is 1.6-2.0. Strong solar proton events in the orbits with the inclination of < 52 degrees result in the dose rate increase up to 2-3 cGy day-1. On the surface of the orbital spacecrafts the daily dose reaches 2 Gy. The neutron dose depends on the shielding mass distribution varying within the limits of 6%-30% of the charged particles dose. In deep space the dose is mainly formed by the galactic and solar cosmic rays(GCR,SCR). Behind the shielding of 2-3 g cm-2 Al the GCR dose varies in the range of (20-30) 10(-5) Gy day-1. The SCR dose can reach hundreds of cSv.     

航天员受银河宇宙线辐射的剂量计算

在近地空间(LEO)和深空探测中,航天员遭受的辐射风险主要来自于银河宇宙线(GCR)照射.银河宇宙线的辐射剂量是航天员辐射风险评价的基础.国际放射防护委员会(ICRP)于2013年提出了新的航天员空间辐射剂量估算方法,以更准确给出空间重离子辐射的剂量.基于此方法,开发了宇宙线粒子在物质中输运的蒙特卡罗程序,并在程序中实现用中国成年男性人体数字模型来仿真航天员.采用该程序计算了粒子(Z=1~92)各向同性照射航天员时器官的通量-器官剂量转换因数,并估算出航天员在近地轨道空间受银河宇宙线辐射的剂量.     

Neoplastic cell transformation by energetic heavy ions and its modification with chemical agents.

For many years we have been interested in understanding the potential carcinogenic effects of cosmic rays. We have studied the oncogenic effects of cosmic rays with accelerator-produced heavy particle radiation and with a cultured mammalian cell system--C3H10T1/2 cells. Our quantitative data obtained with carbon, neon, silicon, and iron particles showed that RBE is both dose and LET dependent for neoplastic cell transformation. RBE is higher at lower dose, and RBE increases with LET up to about 200 keV/micrometer. In nonproliferation confluent cells, heavy-ion induced transformation damage may not be repairable, although a dose modifying factor of about 1.7 was observed for X-ray radiation. Our recent studies with super-heavy high-energy particles, e.g., 960 MeV/U U235 ions (LET = 1900 keV/micrometer), indicate that these ions with a high inactivation cross-section can cause neoplastic cell transformation. The induction of cell transformation by radiation can be modified with various chemicals. We have found that the presence of DMSO (either during or many days after irradiation) decreased the transformation frequency significantly. It is, therefore, potentially possible to reduce the oncogenic effect of cosmic rays in space through some chemical protection.     

Enhancing the ATIC charge resolution

The Advanced Thin Ionization Calorimeter (ATIC) experiment is designed to investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 10¹¹ to 10¹⁴ eV during Long Duration Balloon (LDB) flights from McMurdo, Antarctica. Currently, analysis from the ATIC-1 test flight and ATIC-2 science flight is underway and preparation for a second science flight is in progress. Charge identification of the incident cosmic ray is accomplished, primarily, by a pixilated Silicon Matrix detector located at the very top of the instrument. While it has been shown that the Silicon Matrix detector provides good charge identification even in the presence of electromagnetic shower backscatter from the calorimeter, the detector only measures the charge once. In this paper, we examine use of the top scintillator hodoscope detector to provide a second measure of the cosmic ray charge and, thus, improve the ATIC charge identification.     

Estimation of a cosmonaut's radiation hazard during long-term space missions on the basis of a generalized dosimetric function.

This paper presents a new concept of radiation hazard assessment for spacecraft crew members during long term space missions on the basis of a generalized dosimetric function. This new dosimetric function enables a complicated nature of space radiation exposure to be reduced to the conditions of a standard irradiation. It can be obtained on the basis of mean-tissue equivalent dose values calculated for each space radiation source and transmission coefficients describing the influence of the complex spatial and temporal distribution of the absorbed dose in the cosmonaut's body on the radiobiological effects. The combination of cosmic ionizing radiation with other non-radiation nature factors in flight can also be accounted for. In terms of the generalized dose, it is possible to assess the nature and extent of lowering a crew working capacity, as well as radiation risk, both during a flight and post flight period.     

1998年9月24日地磁暴前宇宙线各向异性特性分析

分析了日本Nagoya 宇宙线闪烁体望远镜30°, 49°, 64° 倾角的东、西、南、北方向探测数据的变化特点, 运用小波分析方法定性地探讨了磁暴前后宇宙线南北、东西各向异性的变化特征. 研究发现, 当发 生大地磁暴时, 地面宇宙线强度的各向异性特征将发生非常大的变化, 这种变化一般在磁暴发生前10~20 h就开始出现. 当描述这种各向异性特征的各向异性指数的小波系数变化达到一定阈值时, 就可能有大地磁暴发生.      

PAMELA observational capabilities of Jovian electrons

PAMELA is a satellite-borne experiment that has been launched on June 15th, 2006. It is designed to make long duration measurements of cosmic radiation over an extended energy range. Specifically, PAMELA is able to measure the cosmic ray antiproton and positron spectra over the largest energy range ever achieved and will search for antinuclei with unprecedented sensitivity. Furthermore, it will measure the light nuclear component of cosmic rays and investigate phenomena connected with solar and earth physics. The apparatus consists of: a time of flight system, a magnetic spectrometer, an electromagnetic imaging calorimeter, a shower tail catcher scintillator, a neutron detector and an anticoincidence system. In this work a study of the PAMELA capabilities to detect electrons is presented. The Jovian magnetosphere is a powerful accelerator of electrons up to several tens of MeV as observed at first by Pioneer 10 spacecraft (1973). The propagation of Jovian electrons to Earth is affected by modulation due to Corotating Interaction Regions (CIR). Their flux at Earth is, moreover, modulated because every 13 months Earth and Jupiter are aligned along the average direction of the Parker spiral of the Interplanetary Magnetic Field.PAMELA will be able to measure the high energy tail of the Jovian electrons in the energy range from 50 up to 130 MeV. Moreover, it will be possible to extract the Jovian component reaccelerated at the solar wind termination shock (above 130 MeV up to 2 GeV) from the galactic flux.     

Computation of radiation environment during ground level enhancements 65, 69 and 70 at equatorial region and flight altitudes

The radiation environment in the troposphere of the Earth is governed by cosmic rays of galactic and solar origin. During major solar energetic particles events the radiation environment changes dramatically. As a results the risk of biological effects due to exposure to ionizing radiation of aircrew increases. Here we present a numerical model for computation of absorbed dose in air due to cosmic rays of galactic and solar origin. It is applied for computation of radiation environment at flight altitude in the equatorial region during several major ground level enhancements, namely GLE65 on 28 October 2003, GLE69 on 20 January 2005 and GLE70 on 13 December 2006. The model is based on a full Monte Carlo simulation of cosmic ray induced atmospheric cascade. The cascade simulation is carried out with CORSIKA 6.990 code with corresponding hadron generators FLUKA 2011 and QGSJET II. The contribution of different cascade components, namely electromagnetic, hadron and muon is explicitly obtained. The spectra of arriving solar energetic particles are calculated from ground level measurements with neutron monitors and satellite data from GOES. The obtained results are discussed.     

Cosmic ray hit frequencies in critical sites in the central nervous system.

One outstanding question to be addressed in assessing the risk of exposure to space travelers from galactic cosmic rays (GCR) outside the geomagnetosphere is to ascertain the effects of single heavy-ion hits on cells in critical regions of the central nervous system (CNS). As a first step toward this end, it is important to determine how many "hits" might be received by a neural cell in several critical CNS areas during an extended mission outside the confines of the earth's magnetic field. Critical sites in the CNS: the macula, and an interior brain point (typical of the genu, thalamus, hippocampus and nucleus basalis of Meynert) were chosen for the calculation of hit frequencies from galactic cosmic rays for a mission to Mars during solar minimum (i.e., at maximum cosmic-ray intensity). The shielding at a given position inside the body was obtained using the Computerized Anatomical Man (CAM) model, and a radiation transport code which includes nuclear fragmentation was used to calculate yearly fluences at the point of interest. Since the final Mars spacecraft shielding configuration has not yet been determined, we considered the minimum amount of aluminum required for pressure vessel-wall requirements in the living quarters of a spacecraft, and a typical duty area as a pressure vessel plus necessary equipment. The conclusions are: (1) variation of the position of the "target site" within the head plays only a small role in varying hit frequencies; (2) the average number of hits depends linearly on the cross section of the critical portion of the cell assumed in the calculation; (3) for a three-year mission to Mars at solar minimum (i.e., assuming the 1977 spectrum of galactic cosmic rays), 2% or 13% of the "critical sites" of cells in the CNS would be directly hit at least once by iron ions, depending on whether 60 micrometers2 or 471 micrometers2 is assumed as the critical cross sectional area; and (4) roughly 6 million out of some 43 million hippocampal cells and 55 thousand out of 1.8 million thalamus cell nuclei would be directly hit by iron ions at least once on such a mission for space travelers inside a simple pressure vessel. Also, roughly 20 million out of 43 million hippocampal cells and 230 thousand out of 1.8 million thalamus cell nuclei would be directly hit by one or more particles with z > or = 15 on such a mission.     

Applications and usage of the real-time Neutron Monitor Database

A high-time resolution Neutron Monitor Database (NMDB) has started to be realized in the frame of the Seventh Framework Programme of the European Commission. This database will include cosmic ray data from at least 18 neutron monitors distributed around the world and operated in real-time. The implementation of the NMDB will provide the opportunity for several research applications most of which will be realized in real-time mode. An important one will be the establishment of an Alert signal when dangerous solar cosmic ray particles are heading to the Earth, resulting into ground level enhancements effects registered by neutron monitors. Furthermore, on the basis of these events analysis, the mapping of all ground level enhancement features in near real-time mode will provide an overall picture of these phenomena and will be used as an input for the calculation of the ionization of the atmosphere. The latter will be useful together with other contributions to radiation dose calculations within the atmosphere at several altitudes and will reveal the absorbed doses during flights. Moreover, special algorithms for anisotropy and pitch angle distribution of solar cosmic rays, which have been developed over the years, will also be set online offering the advantage to give information about the conditions of the interplanetary space. All of the applications will serve the needs of the modern world which relies at space environment and will use the extensive network of neutron monitors as a multi-directional spectrographic detector. On top of which, the decreases of the cosmic ray intensity – known as Forbush decreases – will also be analyzed and a number of important parameters such as galactic cosmic ray anisotropy will be made available to the users of NMDB. A part of the NMDB project is also dedicated to the creation of a public outreach website with the scope to inform about cosmic rays and their possible effects on humans, technological systems and space-terrestrial environment. Therefore, NMDB will also stand as an informative gate on space research through neutron monitor’s data usage.