ABSTRACT
Ionizing radiation in general and mixed fields of space radiation in particular pose a risk of serious harm to human health. The risk of such adverse effects increases with the duration of the mission, and for all missions outside the protective properties of the Earth's magnetic field and atmosphere. Accordingly, radiation protection is of central importance for all human spaceflight, which is recognized by all international space agencies. To date various systems, analyze and determine the exposure to ionizing radiation within the environment and to the crew onboard the International Space Station (ISS). In addition to this operational monitoring, experiments and technology demonstrations are carried out. This to further enhance systems capabilities, to prepare for exploratory missions, to the Deep Space Gateway and/or to enable for human presence at other celestial bodies. Subsequently the European Space Agency (ESA) decided early to support the development of an active personal dosimeter. Under the auspices of the European Space Research and Technology Center (ESTEC) together with the European Astronaut Center's (EAC) Medical Operations and Space Medicine (HRE-OM) team, a European industrial consortium was formed to develop, build, and test this system. To complete the ESA Active Dosimeter (EAD) Technology Demonstration in space, EAD components were delivered to ISS with the ESA's space missions 'iriss' and 'proxima' in 2015 and 2016. This marked Phase 1 (2015) and 2 (2016-2017) of the EAD Technology Demonstration to which focus is given in this publication. All EAD systems and their functionalities, the different radiation detector, their properties, and calibrations procedures are described. Emphasis is first on the "iriss" mission of September 2015, that provided a complete set of data for an entire space mission from launch to landing, for the first time. Data obtained during Phase 2 in 2016-2017 are discussed thereafter. Measurements with the active radiation detectors of the EAD system provided data of the absorbed dose, dose equivalent, quality factor as well as the various dose contributions during the crossings of the South Atlantic Anomaly (SAA) and/or resulting from galactic cosmic radiation (GCR). Results of the in-flight cross-calibrations among the internal sensors of the EAD systems are discussed and alternative usage of the EAD Mobile Units as area monitors at various different locations inside the ISS is described.
Subject(s)
Cosmic Radiation , Radiation Monitoring , Space Flight , Humans , Radiation Dosimeters , Radiation Monitoring/methods , Astronauts , Radiation DosageABSTRACT
Dynamic light scattering (DLS) is a well-known noninvasive technique for investigating interactions of protein molecules in solution. Unfortunately, DLS is not very sensitive to small size changes because covariables, such as temperature, viscosity, and refractive index, are not precisely known, or they vary as functions of an experiment run, making it difficult to resolve subtle size changes of only a few Angstrom. It is usually not possible, if these covariables are not systematically measured and brought into the DLS analysis, to separate monomers from dimers when both are present in solution. We present here measurements with a variant of DLS that determines rotational diffusion as well as translation diffusion. This technique, called depolarized dynamic light scattering (DDLS) is, like DLS, also an old method, but it is rarely used due to enormous practical difficulties. However, we have found that a combination of DLS with DDLS is very promising, because it allows for a rough shape determination of the molecule under study and it is more sensitive to subtle size changes. We built an instrument that overcomes some of the difficulties, and report measurements made with this instrument. One of the samples was Photosystem-I, a membrane protein for photosynthesis. Its dimensions were determined to be 9.6 nm thick and 26 nm in diameter, values that are in good agreement with the dimensions obtained from X-ray diffraction analysis of single crystals.
Subject(s)
Biophysics/instrumentation , Biophysics/methods , Crystallization , Light , Proteins/chemistry , Crystallography , Crystallography, X-Ray , Diffusion , Dimerization , Gravitation , Particle Size , Photosystem I Protein Complex/chemistry , Photosystem II Protein Complex/chemistry , Protein Conformation , Refractometry , Scattering, Radiation , Temperature , Time Factors , X-RaysABSTRACT
A means of controlling crystallization is to separate the phases of nucleation and growth. Methods to achieve this, other than seeding, involve lowering the supersaturation by changing the temperature or diluting drops after incubating them for a given time at nucleation conditions. However, by the time nuclei or crystals are visible under the microscope too many nuclei will have formed. Dynamic Light Scattering was applied practically, to determine the most likely time for nucleation-growth decoupling to be performed successfully. The time at which DLS showed a significant change in the size-distribution of species in solution, corresponded to that optimal time.
