radiation dose distribution within the matroshka … · dramatically enhanced due to the absence of...

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RADIATION DOSE DISTRIBUTION WITHIN THE MATROSHKA HUMAN PHANTOM TORSO

ONBOARD ISS

Final Report Phase A AIAU 27602

TITLE AND SUBTITLE

Radiation dose distribution within the Matroshka human phantom torso onboard ISS

ACRONYM

RADIS-Austria (MATROSHKA-2A)

REPORT TYPE AND DATES COVERED

Technical Paper (1 May 2005 – 30 September 2007)

PERFORMING ORGANIZATION NAME AND ADDRESS

Vienna University of Technology Atomic Institute of the Austrian Universities Stadionallee 2 Vienna, AT−1020

PRINCIPAL INVESTIGATORS

Univ.Prof. i.R. DI Dr. Norbert Vana Univ.Ass. DI Dr. Michael Hajek Telefon +43 1 588 01–141 93 Telefax +43 1 588 01–141 99 E-Mail [email protected]

CO-INVESTIGATORS

DI Robert Bergmann Lucas M. Ellmeier ADir. Ing. Manfred Fugger

Vienna, September 2007 Univ.Ass. DI Dr. Michael Hajek

Vienna University of Technology Atomic Institute of the Austrian Universities

Radiology, Radiation Protection and Nuclear Measurement

Stadionallee 2 Vienna, AT-1020

Austria

Cover illustration: The European Matroshka Phantom experiment was photographed by an Expedition 14 crewmember in the Zvezda Service Module of the International Space Station. (courtesy NASA).

EXECUTIVE SUMMARY The cosmic radiation environment is significantly different from that found terrestrially. Cosmic rays primarily consist of high-energy charged particles originating from galactic and solar sources. Some of these particles inflict greater biological damage than that resulting from terrestrial radiation hazards. Particle and energy spectra are attenuated in interaction processes within the human body. The reliable assessment of health risks to astronaut crews is pivotal in the design of future expeditions into interplanetary space and requires knowledge of absorbed radiation doses in critical radiosensitive organs and tissues. The MATROSHKA experiment is being continued in the frame of the RADIS project – or to use the official European Space Agency (ESA) acronym MATROSHKA-II – and is divided into two phases. Only passive detectors were used in phase A whereas phase B consists of both active and passive detectors. With this project the dose profile in the anthropomorphic phantom body onboard the Russian Segment of the International Space Station (ISS) shall be investigated.

MATROSHKA basically consists of a human phantom torso attached to a base structure. Unlike for the exposure outside the ISS, for inside operation MATROSHKA was not covered by a protective hull which was designed to resemble a spacesuit. The phantom is divided into 33 tissue-equivalent polyurethane slices of specific density for tissue and organs. Natural bones are embedded. Channels and cut-outs enable accommodation of diverse radiation monitors as well as temperature and pressure sensors. The phantom body was equipped with 7 active and more than 6000 passive detectors arranged in a regular grid. Thereof, the Vienna University of Technology—Atomic Institute of the Austrian Universities provided more than 1100 thermoluminescence dosemeter crystals for dose measurements with high spatial resolution and estimation of the biological effectiveness of the radiation field by means of the worldwide unique high-temperature ratio method. MATROSHKA was exposed inside the Russian Segment of the ISS for a period of 11 months, starting with January 2006. The dose profile in the anthropomorphic phantom was investigated to reveal a less steep gradient from the head to the abdomen compared to MATROSHKA-I. In the depth of the body a similar dose gradient was obtained. Furthermore a significant reduction of absorbed doses to the skin and head was found. Dose-related hot spots in particular organs could not be confirmed for the doses accumulated in the eye, lung, stomach, kidney and intestine were below the dose to the skin.

The results of the MATROSHKA programme are expected to improve

both dosimetric metrology and risk estimates for human spaceflight. They are equally important for terrestrial applications, e.g. radiotherapy and aircrew radiation monitoring.

ZUSAMMENFASSUNG Das Strahlenklima im Weltraum unterscheidet sich grundlegend von der terrestrischen Umgebungsstrahlung. Kosmische Strahlung besteht hauptsächlich aus hochenergetischen geladenen Teilchen aus galaktischen und solaren Quellen. Einige dieser Partikel können größere biologische Schäden hervorrufen, als sie durch terrestrische Strahlenexposition zu erwarten sind. Die Teilchen- und Energiespektren werden in Wechselwirkungsprozessen mit dem menschlichen Körper geschwächt und aufgehärtet. In Hinblick auf das Design zukünftiger, interplanetarer Missionen ist eine zuverlässige Erfassung und Bewertung des Strahlenrisikos der Astronautenbesatzung entscheidend. Dies erfordert jedenfalls die Kenntnis der in kritischen, strahlen-empfindlichen Organen und Geweben absorbierten Strahlendosen. Das MATROSHKA-Experiment wird im Rahmen des Projektes RADIS – von der Europäischen Weltraumagentur (ESA) als MATROSHKA-II bezeichnet – weitergeführt und in zwei Phasen unterteilt. Phase A beinhaltet nur passive, Phase B aktive und passive Detektoren. Bei diesem Projekt soll das Dosisprofil in einem anthropomorphen Phantomkörper an Bord des Russischen Segments der Internationalen Raumstation (ISS) untersucht werden.

MATROSHKA besteht im Wesentlichen aus einem an einer Basisplattform angebrachten menschlichen Torsophantom. Im Gegensatz zur äußeren Exposition war MATROSHKA im Inneren der Raumstation nicht von einer Sicherheitshülle zur Simulation eines Raumanzuges umgeben. Das Phantom aus gewebeäquivalentem Polyurethan ist in 33 Schichten unterteilt. Natürliche Knochensubstanz ist eingebettet. Kanäle und Ausfräsungen erlauben die Einbringung diverser Strahlungs- sowie Druck- und Temperatursensoren. Das Phantom wurde mit 7 aktiven und mehr als 6000 passiven, in einem regelmäßigen Raster angeordneten Detektoren ausgestattet. Davon stellte die Technische Universität Wien (Atominstitut der Österreichischen Universitäten) mehr als 1100 Thermolumineszenz-Dosimeterkristalle für Dosismessungen mit hoher Ortsauflösung und die Bewertung der biologischen Wirksamkeit des Strahlenfeldes durch ein weltweit einzigartiges Verfahren zur Verfügung. MATROSHKA wurde für einen Zeitraum von 11 Monaten ab Jänner 2006 im Russischen Segment der ISS befestigt. Das Dosisprofil in dem anthropomorphen Phantomkörper zeigte im Vergleich zu MATROSHKA-I einen deutlich schwächer ausgeprägten Gradienten vom Kopf zum Unterkörper. In die Tiefe des Gewebes konnte allerdings ein ähnlicher Dosisverlauf festgestellt werden. Weiters zeigte sich eine deutliche Reduktion der Strahlenbelastung im Kopfbereich sowie der Haut. Signifikante Dosiserhöhungen in bestimmten Organen konnten dabei nicht bestätigt werden. Die in Auge, Lunge, Magen, Niere und Darm akkumulierten Dosen lagen unterhalb, der Hautdosis.

Die Ergebnisse des MATROSHKA-Programmes lassen eine

Verbesserung sowohl der dosimetrischen Messtechnik als auch der Risikoabschätzung für die bemannte Weltraumfahrt erwarten. Sie sind jedoch gleichermaßen für terrestrische Anwendungen von Bedeutung, etwa im Bereich der Strahlentherapie und der radiologischen Überwachung des fliegenden Personals.

CONTENTS

CONTRACT DETAILS .................................................................3

EXECUTIVE SUMMARY...............................................................4

ZUSAMMENFASSUNG................................................................5

CONTENTS..............................................................................6

ACRONYMS .............................................................................7

1 INTRODUCTION .................................................................8

2 MATROSHKA FACILITY ...................................................... 13

3 MISSION PLANNING ......................................................... 17

4 INSTRUMENTATION AND METHODS..................................... 23

4.1 THERMOLUMINESCENCE ................................................... 23

4.2 APPLICATIONS TO DOSIMETRY............................................ 24

4.3 HEAVY-ION RESPONSE .................................................... 27

4.4 HIGH-TEMPERATURE RATIO METHOD .................................... 30

4.5 ENERGY RESPONSE ........................................................ 32

5 EXPERIMENTAL RESULTS................................................... 34

5.1 DEPTH DOSE DISTRIBUTION.............................................. 34

5.2 ORGAN ABSORBED DOSES................................................ 55

5.3 PONCHO ABSORBED DOSES .............................................. 57

5.4 REFERENCE DETECTOR SETS ............................................. 57

6 DATA INTERCOMPARISON ................................................. 59

6.1 INTERCOMPARISON MATROSHKA-II PHASE A VERSUS MATROSHKA-I 59

6.2 INTERNATIONAL INTERCOMPARISON...................................... 63

7 CONCLUSIONS................................................................. 66

8 PUBLICATIONS ................................................................ 67

APPENDIX A .......................................................................... 68

REFERENCES......................................................................... 83

ACRONYMS AT ................. Acceptance test ATI ................ Atomic Institute of the Austrian Universities BFO .............. Blood-forming organs BNL............... Brookhaven National Laboratory CCD.............. Charge coupled device CME.............. Coronal mass ejections CNS .............. Central nervous system CT................. Computer tomography DLR............... Deutsches Zentrum für Luft- und Raumfahrt (German

Aerospace Centre) DNA .............. Deoxyribonucleic acid DOSTEL ....... Dosimetry telescope ESA............... European Space Agency EVA............... Extra-vehicular activity GCR.............. Galactic cosmic ray HCP .............. Heavy charged particle HIMAC .......... Heavy Ion Medical Accelerator in Chiba HTR .............. High-temperature ratio INP................ Institute of Nuclear Physics ISS................ International Space Station LEO............... Low-Earth orbit LET ............... Linear energy transfer LINAC ........... Linear accelerator NASA............ National Aeronautics and Space Administration NCRP............ National Council on Radiation Protection and

Measurements NIRS ............. National Institute of Radiological Sciences NSRL ............ NASA Space Radiation Laboratory NTDP............ Nuclear track detector package OSL............... Optically stimulated luminescence OSLD............ Optically stimulated luminescence detector OSU.............. Oklahoma State University PM ................ Photomultiplier PNTD............ Plastic nuclear track detector RBE .............. Relative biological effectiveness RSC .............. Russian Space Centre SCR .............. Solar cosmic radiation SPE............... Solar energetic particle event SSD .............. Silicon scintillation detector STS............... Space Transportation System TEPC ............ Tissue-equivalent proportional counter TL.................. Thermoluminescence TLD............... Thermoluminescence Dosemeter Z.................... Nuclear charge

1 INTRODUCTION The cosmic ray environment in low-Earth orbit (LEO) is mainly composed of high-energy charged particles originating from galactic sources, solar energetic events and radiation confined within the dipolar geomagnetic field. Galactic cosmic ray (GCR) fluxes are determined essentially by protons (85 %) and alpha particles (12 %), with the remainder being highly ionized heavier ions with charges of Z = 2 to 92 (Figure 1.1). Energy spectra extend from a few MeV amu−1 to several GeV amu−1 (Figure 1.2). Solar cosmic radiation (SCR) is emitted regularly as solar wind and consists of electrons, protons, some heavier nuclei and electromagnetic waves over virtually all wavelengths. However, the major radiation hazard from the sun is related to sporadic outbursts from the solar corona (Figure 1.3), so-called solar energetic particle events (SPE), comprising the effects of solar flares and coronal mass ejections (CME). In the course of such events, large amounts of energy are released in many forms: electromagnetic (radio waves, gamma- and X-rays), energetic particles (electrons and protons) and mass flows. As electromagnetic emissions propagate faster and are not deflected by the interplanetary magnetic fields they may be utilized advantageously for space weather alerts and warnings.

Life on our home planet is shielded from cosmic radiation by the geomagnetic field and the absorbing effect of approximately 1020 g cm−2 of atmospheric air. This protection is sufficiently effective that at sea level a dose rate of only about 0.8 µSv d−1 is observed—mainly accumulated from muons produced in interactions of primary cosmic rays with the atmosphere. Unlike on ground, particle fluxes in LEO are dramatically enhanced due to the absence of the atmospheric shield. Although protected by its hull structure, the shielding efficiency of a spacecraft is generally much lower than that of the Earth. As a consequence, high-energy GCR and SCR particles can easily penetrate its walls and interior. Additionally, a spacecraft in LEO is exposed to high-energy electrons and protons trapped in the Earth’s radiation belts. Exposure levels inside spacecraft at an altitude of 400 km, i.e. the average orbital altitude of the International Space Station (ISS), can be as high as 1 mSv d−1. During a nominal extra-vehicular activity (EVA) the radiation load on astronauts is possible to reach about 1 mSv per excursion. A major SPE may well increase exposure levels by a factor of 100 and more.

Radiation exposure of astronauts has been identified by the responsible space authorities as a major—perhaps the most severe—risk in human space flight and as a limiting factor in the design of future space exploration, particularly long-term interplanetary

INTRODUCTION 9

FIG. 1.1. Percentage contributions from individual GCR elements for the particle flux, absorbed dose and dose equivalent at solar minimum (Cucinotta et al., 2003).

FIG. 1.2. Fluence rate of cosmic-ray particles as a function of energy (Wilson et al., 1991).

FIG. 1.3. Proton fluxes for different energy intervals measured during the significant solar energetic particle events in October 2003 (SEC/NOAA, 2003).

INTRODUCTION 10

missions. The radiations encountered in space can pass through shielding with differing levels of penetration and can ultimately inflict biological damage from ionizing dose effects that are hazardous to the crew. The expected exposure levels in long-term work shifts on a space station surpass by far the limits for occupational radiation exposure at terrestrial workplaces, implying that the concepts of terrestrial radiation protection are not applicable to space-borne operations. Radiation protection authorities defined career exposure limits (Table 1.1) in accordance with a lifetime excess risk of fatal cancer ≤ 3 % (Fry et al., 2000). More important, the National Council on Radiation Protection and Measurements (NCRP) proposed the implementation of limits for preventing deterministic radiation effects (Table 1.2) that incorporates a relative biological effectiveness (RBE). Dose limits for such effects are expressed as Gray-equivalent (Gy-Eq)—a dose weighted for RBE. This is a significant change from the prior use of radiation quality factors that are based on data for late effects, most importantly cancer, although few studies with heavy charged particles (HCP) have been made for determining both short-term and career limits. Based on these new NCRP recommendations, more emphasis on research for determining the appropriate RBE values for deterministic effects, particularly after exposure to ultra-high energy heavy ions and their secondaries are needed. Deterministic effects on the crew, including acute radiation sickness, damage to the central nervous system (CNS) and blood-forming organs (BFO) or cataracts, occur only above dose thresholds. The probability of stochastic effects to occur, such as cancer, hereditary effects or neurological disorders, is proportional to dose. TABLE 1.1. Career radiation dose limits for late effects

10-year career exposure limit (Sv)

Age (yr) Male Female

25 0.7 0.4

35 1.0 0.6

45 1.5 0.9

55 3.0 1.7

Source: Fry et al. (2000). TABLE 1.2. Radiation dose limits for deterministic effects

Dose limit (Gy-Eq)

Anatomy 30-day limit 1-year limit

Eye 1.0 2.0

Skin 1.5 3.0

BFO 0.25 0.50

Source: Fry et al. (2000).

Due to their high ionization density, expressed by the linear energy transfer (LET), cosmic rays potentially inflict greater biological damage than that resulting from typical terrestrial radiation hazards. The

INTRODUCTION 11

investigation of radiobiological action and damage on a microscopic level seems of particular importance since radiation-sensitive targets such as deoxyribonucleic acid (DNA)—the carrier of genetic information—are concentrated mostly in the cellular nucleus. Depending on the type of particle, the ionizations along its path are more or less closely spaced. LET is used to describe the situation and is defined as the amount of locally absorbed energy per unit path length, commonly stated in multiples of keV µm−1. The attribute ‘locally’ is of special interest since it postulates that only the energy fraction leading to ionizations and/or excitations within the considered volume is counted. HCP and neutrons are characterized as high-LET radiations because they produce an extremely dense linear track of ionization and excitation events along their passage through matter (Figure 1.4). Thus, they are likely to cause multiple damage at the same site and their biological effectiveness is dramatically enhanced. In contrast, gamma-rays and electrons produce a more uniform distribution of ionization events and are considered to be low-LET radiations. A LET value of 10 keV µm−1 is commonly accepted as dividing line between low- and high-LET radiations.

Particle and energy spectra are attenuated in interaction processes within shielding structures and the human body. Reliable assessment of health risks to astronaut crew, particularly cancer induction, is pivotal in the design of future expeditions into interplanetary space and related to the estimation of radiation doses at the level of critical radiosensitive organs and tissues. As organ dose equivalents are not directly measurable, anthropoid phantoms need to be used. Previous experimental studies in LEO included a phantom head from the National Aeronautics and Space Administration (NASA) which was flown on board three Space Shuttle missions (Konradi et al., 1992). A Russian experiment with Austrian participation determined the dose distribution in a simple water-filled phantom sphere on board the Mir Orbital Station (Berger et al., 2001, 2002, 2004). A NASA phantom torso was exposed on board the ninth Shuttle-Mir mission STS-91 (Yasuda et al., 2000) and, more recently, on board the US Destiny Laboratory Module of the ISS (Badhwar et al., 2002). The most extensive joint research effort, however, was initiated by the

FIG. 1.4. Monte Carlo-simulated tracks of (a) a typical HCP and of (b) an electron (Horowitz et al., 2001).

TABLE 1.3. Laboratories participating of the MATROSHKA-II experiment

Laboratory Investigator(s)

Boeing Space Systems (US) Atwell W

Chalmers University of Technology (SE) Shiver L

INTRODUCTION 12

Christian-Albrechts-Universität zu Kiel (DE) Beaujean R

Dublin Institute for Advanced Studies (IE) O’Sullivan D

Eril Research Inc. (US) Benton E

German Aerospace Center (DE) Reitz G

Health Protection Agency (GB) Bartlett D

Henrik Niewodniczanski Institute of Nuclear Physics (PL) Bilski P, Olko P

Institute for Biomedical Problems (RU) Akatov Y, Shurshakov V

Istituto Nazionale di Fisica Nucleare (IT) Casolino M, Grossi G

Japan Aerospace Exploration Agency (JP) Nagamatsu A, Yoshitomi S

KFKI Atomic Energy Research Institute (HU) Pálfalvi J

Lawrence Berkeley National Laboratory (US) Miller J, Zeitlin C

National Aeronautics and Space Administration (US) Cucinotta F, Semones E

National Institute of Radiological Sciences (JP) Uchihori Y

Oklahoma State University (US) McKeever S, Yukihara E

Physikalisch-Technische Bundesanstalt (DE) Luszik-Bhadra M

Vienna University of Technology (AT) Hajek M, Vana N

European Space Agency (ESA) in developing the anthropomorphic phantom body MATROSHKA (Dettmann and Reitz, 2003) which is described in detail in Chapter 2. Table 1.3 provides an overview of the renowned laboratories having joined the MATROSHKA-II project.

2 MATROSHKA FACILITY The MATROSHKA facility basically consists of an Alderson-type human phantom torso attached to a base platform and covered by a protective carbon-fibre container, acting as a spacesuit model (Figure 2.1), which has been removed for the internal exposure. The phantom is divided into 33 nearly tissue-equivalent, polyurethane-based slices of specific density for tissue and organs, aligned along a central rod (Figure 2.2). Natural bones are embedded. 356 channels and cut-outs enable accommodation of 7 active and more than 6000 passive radiation sensors. Active devices included different types of silicon scintillation detectors (SSD), a silicon telescope (DOSTEL) and a tissue-equivalent proportional counter (TEPC). Passive detectors comprised thermoluminescence (TL) and optically stimulated luminescence (OSL) dosemeters as well as plastic nuclear track detector (PNTD) sheets. Additional detectors were implemented in 5 boxes at the sites of radiosensitive organs (eye, lung, stomach, kidney and intestine). A sixth box was mounted on top of the head. To simulate the skin, the phantom was dressed by a hood (Figure 2.3) and a poncho (Figure 2.4). Skin doses were measured on the anterior, posterior and lateral sides of the torso with the detectors housed in polyethylene boxes sued to the phantom surface (mid thorax, upper abdomen, lateral right and left sides, mid dorsal and lumbar). After the facility had been sealed by the containment, it was coated with a protective multilayer insulation (MLI) to which detector boxes had been attached (Figure 2.5). An animated computer tomography (CT) image of the MATROSHKA phantom torso can be viewed at http://www.dlr.de/matroshka.

http://www.dlr.de/matroshka

MATROSHKA FACILITY 14

FIG. 2.1. Schematic drawing illustrating the design of the MATROSHKA facility (courtesy DLR).

FIG. 2.2. The MATROSHKA torso is cut into 33 slices for dosemeter integration (courtesy DLR).


FIG. 2.3. Matroshka wears a hood to simulate the skin (courtesy DLR).

FIG. 2.4. MATROSHKA wearing a poncho to simulate the skin (courtesy DLR).


FIG. 2.5. A multi-layer insulation is used to protect the Matroshka facility from environmental effects and space debris (courtesy DLR).

FIG. 2.6. Layout of the TL detector tubes distributed within the MATROSHKA torso (courtesy DLR).

The Vienna University of Technology–Atomic Institute of the Austrian Universities (ATI) provided 942 thermoluminescence dosemeter (TLD) chips for insertion into 89 detector tubes in 14 different slices of the MATROSHKA phantom torso. A few more hundred TLD chips were used for dose measurements in the organ and poncho detector boxes. A total number of slightly more than 1100 detectors from ATI accounted for about one fifth of the passive radiation detector set used in the MATROSHKA-II phase A experiment. A detailed illustration of the dosemeter distribution within the 14 relevant slices can be found in Appendix A. In the Figures, the detector chips of the participating laboratories are represented by different colours, with dark blue referring to dosemeters from ATI. Each tube (Figure 2.6) is identified properly by a label containing a code composed of the slice number and the lateral position of the tube within the slice.

The flight hardware had to pass two acceptance tests (AT). AT-1 was conducted in Cologne, Germany, under the auspices of specialists from RSC Energia. AT-2 was performed in Moscow, Russia, shortly before the launch and was aimed to verify the completeness of the flight hardware which had been delivered to Moscow by representatives from ESA and the German Aerospace Centre (DLR).

3 MISSION PLANNING The detector upload for the MATROSHKA-II phase A experiment was launched to the ISS from the Kazakh Cosmodrome Baikonur on December 21 2005, 19:38 CET on board an unmanned Russian Progress M-55 freighter (mission 20P) carried by a Soyuz-U rocket. The cargo ship docked to the station's Pirs Docking Compartment two days later at 20:46 CET. The entire process of fully automated rendezvous, closure, final approach and capture, followed by closing of hooks and latches, went smoothly and without issues. The integration of the passive detectors on board the Russian Zevzda Module were performed by Flight Engineer One Valery Tokarev and Commander William McArthur from 09:30 to 13:30 CET on January 5 2006 during ISS Expedition 12. Disintegration of the passive detectors took place on December 7 2006 carried out by Flight Engineer Two Thomas Reiter from 22:20 to 23:20 CET during ISS expedition 14. They were downloaded to Earth on board STS-116 December 22 2006. The Space Shuttle arrived safely at the Kennedy Space Center at 10:32 CET. Photographies of launch and return along with some impressions of the ISS environment and portraits of the crews are presented in Figures 3.1 to 3.12. TABLE 3.1. Timetable for the MATROSHKA-II experiment phase A

Date Event Crew Expedition

Dec. 21 2005 New detector upload – Start of MATROSHKA -II Phase A – with Progress 20P freighter

Dec. 23 2005 Docking of Progress 20P cargo ship to ISS

Jan. 05 2006 Integration of the passive detector set into the MATROSHKA facility

W. McArthur, V. Tokarev

ISS-12

Dez. 07 2006 Dismounting of the passive detectors from the MATROSHKA facility

T. Reiter

Dez. 19 2006 Undocking of Discovery from ISS

Dez. 22 2006 Landing of Discovery with passive radiation sensors

ISS-14

MISSION PLANNING 18

FIG. 3.1. Launch of Progress 20P freighter from Baikonur, Kazakhstan (courtesy RSC Energia).

FIG. 3.2. Flight Engineer V. Tokarev begins with setup of the MATROSHKA-II experiment (courtesy NASA).

FIG. 3.3. V. Tokarev is assembling the MATROSHKA facility with the passive detector set (courtesy NASA).

MISSION PLANNING 19

FIG. 3.4. The MATROSHKA facility with the passive detector set (courtesy NASA).

FIG. 3.5. The MATROSHKA phantom mounted in the Zvezda Module (courtesy NASA).

FIG. 3.6. The MATROSHKA phantom mounted in the Zvezda Module (courtesy NASA).

MISSION PLANNING 20

FIG. 3.7. Astronaut T. Reiter disassembling the MATROSHKA facility (courtesy NASA).

FIG. 3.9. Disintegration of passive detectors from the MATROSHKA phantom slices (courtesy NASA).

FIG. 3.8. Nomex® bags for download of the dosimeter tubes to Earth (courtesy DLR).

MISSION PLANNING 21

FIG. 3.10. Landing of the Space Shuttle Discovery, returning the ISS-14 crew along with the MATROSHKA-II dosimeter sets to Earth (courtesy NASA).

FIG. 3.11. ISS-12 crew W. McArthur and V. Tokarev (courtesy NASA).

FIG. 3.12. ISS-13 crew T. Reiter, P. Winogradow and J. Williams (courtesy NASA).

MISSION PLANNING 22

The MATROSHKA-II experiment is going to be continued with ATI

participation in the frame of phase B. The phantom is exposed inside the Zvezda Module without particular shielding from the containment. Active radiation sensors were not allowed to be activated in phase A until extensive safety procedures and test routines for on-board utilization were passed successfully. Phase B shall be initiated on March 9 2007 (Soyuz-14S) and comprise exposure of both active and passive detectors inside the Station for a period of 6 to 9 months. A third phase to study the effects of the solar cycle is discussed between the relevant space authorities.

4 INSTRUMENTATION AND METHODS Radiation dosimetry in complexly mixed radiation fields such as the harsh space environment is usually associated with extensive instrumentation in order to account for the variety of particles and energies involved. Nuclear collisions along the particle trajectory cause the build-up of secondary reaction fragments, both from the projectile and the target. A correct assessment of the biological effectiveness of such a radiation field is aggravated by the fact that, in principle, a separate detector for each of its components is required. Many applications strongly call for measurement techniques featuring high spatial resolution. In this regard, solid-state TL detectors have proven to be reliable instruments to determine the absorbed radiation dose. The commercial production of TL materials in powder form, as hot-pressed and extruded ribbons, chips, rods, capsules or Teflon® discs has greatly influenced their acceptance and lead to widespread use in different segments of environmental and medical radiation protection (McKeever, 1985).

Previously conducted experiments lead to considerable evidence that there are certain conceptual parallels between the action of radiation in biological tissue and solid-state TL detectors (Noll et al., 2000). Specific TL properties exhibit a significant dependence on radiation quality (Schöner et al., 1999), and the molecular crystal structure of approximately nanometre dimensions is believed to be—in some aspects—similar in its response to the effects of ionization density in DNA. This analogy points to the potential of applying TLDs as a solid-state nanodosemeter in mixed radiation fields of unknown composition. 4.1 THERMOLUMINESCENCE The effect of thermally stimulated radioluminescence, shortly termed thermoluminescence, describes the emission of light from an electrical insulator following the previous absorption of energy from ionizing radiation. This is not to be confused with black-body radiation emitted from a substance when heated to incandescence. The luminescence properties of a material are a consequence of structural defects and impurities in the crystal lattice and may be outlined briefly within the energy band theory of solids (Figure 4.1). In an ideal crystal, the periodically varying potential causes the electronic energy levels to be broadened into ‘allowed’ energy bands separated by ‘forbidden’ zones. The highest filled band is termed the valance band and is separated by several electron volts

INSTRUMENTATION AND METHODS 24

FIG. 4.1. Common electronic transitions in a two-level model of a crystalline TL phosphor. Electrons are represented by solid symbols, holes by open symbols. Refer to the text for explanation.

from the lowest unfilled band called the conduction band. Intrinsic and extrinsic lattice defects such as vacancies, interstitials or impurities cause a breakdown in the periodicity of the crystalline structure, thereby inducing further discrete energy levels in the otherwise forbidden zone. It is important to notice that the valence and conduction bands extend throughout the crystal, whereas the defect states are centred upon the defects themselves, i.e. they are localized. Ionizing radiation excites an electron out of the valence band into the conduction band leaving a positive vacancy, shortly termed a ‘hole’, behind in the valence band (transition (a) in Figure 4.1). Thus, ionization creates free electron-hole pairs which may wander through the crystal until they are trapped and become localized by the Coulombic potential of a defect site (transition (b)). The position of the localized energy level within the band gap is determined by the energy required to free the electron from the trapping centre. If the temperature is raised, the traps are emptied successively (transition (c)). The electrons may recombine by one of the several possible transitions depicted in Figure 4.1, emitting their excess energy as TL light (stimulated by transition (g)), or, with much lesser probability, get re-trapped. Additionally, direct and indirect transitions between localized energy levels—particularly within the same atom—may take place, without the involvement of thermal excitation of the trapped electrons into the delocalized conduction band (transition (h)). The excess energy is not necessarily converted into TL light but may as well be dissipated by phonon interaction (non-radiative recombination). 4.2 APPLICATIONS TO DOSIMETRY The configuration of TL recording equipment as commonly applied to radiation dosimetry is illustrated in Figure 4.2. Its nucleus is a light detection system—usually a photomultiplier (PM) tube, a photodiode or a charge coupled device (CCD) element—a sample heater and a temperature control unit. The reader used by ATI was developed in-


FIG. 4.2. Block diagram of the experimental arrangement for recording thermoluminescence, including emission spectra (McKeever, 1985).

house for dosimetric and archaeometric purposes. It facilitates an EMI 9635 QB PM tube with adjustable optical filters and a sample chamber that can be evacuated and flooded with inert high-purity nitrogen during the readout process to prevent from any non-radiation induced light emissions, e.g. due to external contaminants, triboluminescence, chemical reactions etc. (German and Weinstein, 2002).

Light intensity is recorded as a function of temperature by a microprocessor-controlled device. The resulting curve—commonly termed the glow curve—shows a number of distinct peaks whose height is proportional to the absorbed dose. The shape of the glow curve and the number of peaks is characteristic for the TL phosphor in use. During the MATROSHKA experiment the following detector types were employed: CaF2:Tm (TLD-300), 6LiF:Mg,Ti (TLD-600) and 7LiF:Mg,Ti (TLD-700). The detector chips have been purchased from the Austrian sales representative of the Thermo Electron Corporation (former Harshaw Chemical Co.). The annealing and readout protocols differ from type to type (Table 4.1), except that linear heating at a rate of 5°C s−1 was applied. Routine dosimetry usually exploits glow peaks of sufficient thermal stability for dose determination—peak 5 for LiF:Mg,Ti and LiF:Mg,Cu,P which reaches its maximum intensity at 220°C, and peak 5 (250°C) for CaF2:Tm. TABLE 4.1. Annealing and readout protocols for the TL phosphors used by ATI in the MATROSHKA experiment


TL phosphor Trade name Annealing Readout

CaF2:Tm TLD-300 400°C (1.5 h) max 400°C 6LiF:Mg,Ti TLD-600 400°C (1 h) max 480°C 7LiF:Mg,Ti TLD-700 400°C (1 h) max 480°C

FIG. 4.3. Batch variation of TLD-600 TL response, expressed by the calibration factor.

FIG. 4.4. Batch variation of TLD-700 TL response, expressed by the calibration factor.

The detector chips were calibrated individually in terms of gamma-equivalent absorbed dose to water before their use in the MATROSHKA phantom body. Calibration was conducted at the 60Co gamma-theratron of the Clinic of Radiotherapy and Radiobiology–Vienna Medical University, at a dose level corresponding to the expected exposure in space. The chips were pre-selected according to their absolute response (Figures 4.3 and 4.4).


4.3 HEAVY-ION RESPONSE When TL detectors are used in radiation fields of high ionization density, it is essential for correct interpretation of the measured data to consider their dose response characteristics. The dose response function for LiF:Mg,Ti phosphors (TLD-600, TLD-700) is linear up to ~ 10 Gy. For higher doses it starts to become supralinear, followed by a sublinear, saturation-like behaviour in the kGy region (Figure 4.5). In penetrating the phosphor, heavy charged particles deposit extremely high doses in microscopic volumes around the particle track. This causes the registration efficiency of the dosemeter for heavy ions to be different from that for gamma-rays.

FIG. 4.5. Dose response for LiF:Mg,Ti detectors measured after exposure to a 90Sr–90Y beta source (Source: Schöner, 1997).

FIG. 4.6. Schematic cut-away view of the NIRS–HIMAC high-energy accelerator facility in Chiba, Japan (courtesy NIRS).


FIG. 4.7. The Biological Irradiation Room at the NIRS–HIMAC facility in Chiba, Japan.

Relative efficiencies of different types of TL detectors were determined from exposing the detectors to beams of 4He (150 MeV amu−1), 12C (290 and 400 MeV amu−1), 16O (400 MeV amu−1), 20Ne (400 MeV amu−1), 28Si (490 MeV amu−1), 40Ar (500 MeV amu−1), 56Fe (500 MeV amu−1), 84Kr (400 MeV amu−1) and 132Xe (290 MeV amu−1) ions available from the National Institute of Radiological Sciences–Heavy Ion Medical Accelerator (NIRS–HIMAC) in Chiba, Japan (Figure 4.6). The choice of particle species and energy was focused on their abundance in cosmic radiation. To achieve LET variation, particle energy was attenuated with the help of water-equivalent binary filters. Thus, it was possible to cover practically the entire LET range of cosmic rays (Doke et al., 2001). An ionization chamber and plastic nuclear track detectors (PNTD) were used as reference instruments.

The NIRS–HIMAC is probably the most reliable high-energy accelerator for heavy ions worldwide. Initially intended for medical purposes—particularly the treatment of tumour patients with 1H and 12C ions—the HIMAC increasingly developed to a leading scientific facility. Several linear accelerators (LINAC) and two ring synchrotrons are fed by variable ion sources. Beam lines lead into three clinical and four experimental treatment rooms. The facility is able to accelerate particles up to energies between 100 and 800 MeV amu−1. All exposures were realized in the Biological Irradiation Room (Figure 4.7), for the available maximum beam diameter of 10 cm guaranteed a homogeneous dose distribution over the area of the detector packages. Due to the long established cooperation between ATI and NIRS the beam time was provided free of charge. Furthermore, ATI was invited to participate in the Intercomparison of Cosmic Rays with Heavy Ion Beams at NIRS (ICCHIBAN) project, intended to compare the reading of active and passive detectors from the MATROSHKA investigators under identical exposure conditions. For the so-called blind exposures, the beam composition was kept unknown to the participants until all results had been submitted. Two examples of a simulated LEO exposure and a mono-energetic 12C beam (Figures 4.8 and 4.9) demonstrate that ATI results were reliably close to the reference dose values.


FIG. 4.8. Intercomparison of results from ICCHIBAN 2, Blind No. 1 under space-like exposure conditions.

FIG. 4.9. Intercomparison of results from ICCHIBAN 4, Blind No. 8 composed of mono-energetic 12C ions.

Figure 4.10 shows that TL efficiency of 7LiF:Mg,Ti (TLD-700) depends

on both particle species and LET. An over-response of a few percent is observed for protons and alpha particles, whereas the relative TL efficiency decreases significantly for heavier ions. For mixed radiation fields, it is possible to determine a curve fit as a function of LET and calculate from it the effective TL efficiency which is needed to correct the measured doses. The picture is different for CaF2:Tm (TLD-300): relative TL efficiency is comparably close to unity, implying that there is no need for correction of measured dose values (Figure 4.11).


FIG. 4.10. Relative TL efficiency of 7LiF:Mg,Ti (TLD-700) for different particle types and LET.

FIG. 4.11. Relative TL efficiency of CaF2:Tm (TLD-300) for different particle types and LET.

4.4 HIGH-TEMPERATURE RATIO METHOD To permit correction of the measured doses for effective TL efficiency in mixed radiation fields of mostly unknown composition it is essential to determine at first the effective LET. For this purpose, the high-temperature ratio (HTR) method was developed at ATI. By analysis of the well-investigated LET-dependent high-temperature TL emission in LiF:Mg,Ti phosphors (Schöner et al., 1999) information about the ionization density—expressed by the effective LET—can be extracted (Figure 4.12). The HTR is defined as the ratio of the high-temperature intensities for the radiation under study, ξχ, and a reference radiation (60Co gamma-rays), ξγ,


FIG. 4.12. LET-dependence of the high-temperature emission in TLD-700 (normalized to peak 5).

≡ ⋅HTR γ χ

χ γ

δ ξδ ξ

, (4.1)

where δχ and δγ are the corresponding intensities of the main dosimetry peak 5. For our experimental setup, ξχ and ξγ are determined by the integral TL emission in the temperature range from 248 to 310 °C. Calibrations with HCP available from the NIRS–HIMAC established a functional relationship of HTR in dependence on LET (Figure 4.13). Linearity of the HTR with absorbed dose was verified up to 100 mGy (Figure 4.14). Once the effective LET, Leff, is known, the effective efficiency, ηeff, can be derived by applying the curve fit shown in Figure 4.10:

+ ⋅

=+ ⋅

effeff

eff

1 a Lb c L

η . (4.2)

FIG. 4.13. LET-dependence of the high-temperature ratio.


FIG. 4.14. Linearity of the high-temperature ratio with absorbed dose.

where a, b and c are empirical constants. Correction of measured dose values for TL efficiency can now be achieved in two steps: (i) the effective LET is assessed from the HTR, and (ii) is further utilized to determine effective TL efficiency according to Equation (4.2). A plot of TL efficiency over HTR shall further illustrate the correlation (Fig. 4.15). Similar techniques of TL efficiency correction—based on the methodology developed by ATI—were investigated and applied by Yukihara et al. (2004) and Bilski et al. (2004).

FIG. 4.15. Relative TL efficiency of TLD-700 as a function of HTR.

4.5 ENERGY RESPONSE Interpretation of the measured doses should also take into account the energy dependence of TL response for the phosphors employed. Whereas LiF detectors behave almost tissue-equivalent for a broad range of photon energies, CaF2 shows a significant over-response to


low-energy radiations. This fact is particularly important whenever significant bremsstrahlung components are generated. The situation is illustrated by Figure 4.16 showing the ratio of the mass energy absorption coefficients, µen/ρ, for the respective phosphor and tissue:

( ) ( )( ) ( )= ⋅en det

en ref

S E Eµ ρ

ηµ ρ

, (4.3)

where S denotes the energy-dependent response and η the relative efficiency of the detector.

FIG. 4.16. Calculated energy dependence of the TL response for LiF and CaF2 phosphors relative to tissue.

5 EXPERIMENTAL RESULTS 5.1 DEPTH DOSE DISTRIBUTION In total, more than 1100 TL detectors from ATI were dispersed over the MATROSHKA phantom body. Of those, 942 dosemeter crystals of 3.2×3.2×0.9 mm3 in size were inserted into tubes to be placed in 14 of the 33 torso slices (Appendix A). The detectors were read out in the ATI laboratory and analyzed according to the methods outlined in Chapter 4. A post-flight calibration in terms of absorbed dose to water was conducted at the 60Co gamma-theratron of the Clinic of Radiotherapy nd Radiobiology–Vienna Medical University to verify that the TL response was not altered through the space exposure.

The temperature and pressure variations within the course of the MATROSHKA experiment were not recorded by sensors accommodated in the torso due to the fact that no active instruments were used during phase-A. It can be assumed that only very small temperature and pressure variations occurred since the atmosphere in the compartments of the station are well regulated. It can thus be concluded that fading does not require further consideration. The ISS orbit was rather stable during exposure at around 400 km altitude, a very stable inclination of 51,63° and eccentricity of 0,0002285°. It has to be noted that a lower orbit occurred during the pause of NASA’s Space Shuttle programme which was resumed with STS-116.

Absorbed dose and HTR measured in the MATROSHKA slices with 6LiF:Mg,Ti (TLD-600) and 7LiF:Mg,Ti (TLD-700) detectors are given numerically in Tables 5.1 to 5.14. The dose distribution in the respective slices is presented by means of interpolated three-dimensional graphs in Figures 5.6 to 5.19. The applied coordinate system is illustrated in Figure 5.5: the abscissa points in anteroposterior (AP) direction, the ordinate is oriented laterally. The coordinate origin is defined by the MATROSHKA central rod along which the slices are stapled. Effective TL efficiency can be estimated from the HTR (Figure 4.15) to be ~1.12 for both TLD-600 and TLD-700 detectors. This value will be verified by further calibrations that are realized under the MATROSHKA project in high-energy proton fields (2.5 GeV) available from the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). Estimating the dose contribution from thermal neutrons by the method described below is based on the uncorrected absorbed doses in TLD-600 and TLD-700 detectors. Efficiency correction can be achieved by dividing the numbers by 1.12.

In general, a twofold dose gradient was observed: (i) from the head to the abdomen and (ii) in the depth of the phantom body. The slope is steeper atop the head and the upper part of the body. These results confirm the findings of previous experiments with a simplified phantom—a spherical water-filled body—exposed on board the Mir Orbital Station

CONCLUSIONS 35

(Berger et al., 2001, 2004). In both experiments, no dose-related hot spot was found at the level of specific organs but rather was the skin dose a conservative estimate of the whole-body exposure.

Absorbed doses determined with TLD-600 are biased by disproportionate contributions from thermal and epithermal neutrons with energies <200 keV which are detected via the 6Li(nth,α)3H reaction. Neutrons are not encountered in free space but are created in nuclear interactions and as projectile and target fragments within the shielding structures of the spacecraft and the phantom torso itself. The neutron energy spectrum is expected to contain two components—a hadron cascade peak around 100 MeV and a broader peak including evaporation and slowing-down neutrons around 1 MeV. This spectrum is moderated by passage through the simulated space suit and the human body until the neutrons reach thermal energies. The difference between TLD-600 and TLD-700 absorbed doses is a measure of the thermal neutron fraction. The HTR measured in TLD-600 is regarded as an even more sensitive indicator for the presence of thermal neutrons. The contribution from slow neutrons to the overall absorbed dose increases from the head to the abdominal parts and in the depth of the phantom.

No extraordinary solar irregularities have been observed except for a SPE in July 2006 and a stronger SPE in December 2006 (Figure 5.1).

FIGURE 5.1. Integrated Proton Flux during exposure monitored by GOES geostationary satellites

The doses presented in Tables 5.1 to 5.14 have been corrected for

the ambient background accumulated during detector storage on ground and inside the ISS, respectively, as general guidelines shall be agreed between the participating laboratories on how to account for these small doses. A rough estimation of the ambient dose background leads to a value of about 8 to 10 mGy. TLD-700 have been TL-efficiency corrected as shown in chapter 4. Applying the principles of error propagation, the precision of each dose and HTR value is ±12.7 %.

CONCLUSIONS 36

TABLE 5.1. Absorbed dose and HTR determined from TLD-600 (6LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) measurements for MATROSHKA slice 3 (eye plane)

TLD-600 TLD-700

Slice 3 Absorbed dose (mGy) HTR

Absorbed dose (mGy) HTR

A2 80 2.496 61 1.506

A1 100 2.315 67 1.489

B5 89 2.590 70 1.433

B4 85 2.982 62 1.465 B3 86 3.187 61 1.509 B2 95 3.122 56 1.448 B1 102 2.917 54 1.485

C2 102 2.944 60 1.500

C1 88 3.355 56 1.467

D2 85 2.921 61 1.473

D1 95 3.374 51 1.499

E4 84 2.679 65 1.475

E3 83 3.230 55 1.449 E2 89 3.562 55 1.461 E1 79 3.456 55 1.462

F3 95 2.498 62 1.495

F2 94 2.613 65 1.439 F1 94 2.575 58 1.482

CONCLUSIONS 37

TABLE 5.2. Absorbed dose and HTR determined from TLD-600 (6LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) measurements for MATROSHKA slice 7

TLD-600 TLD-700



A3 99 2.685 60 1.464

A2 79 2.820 59 1.506 A1 97 2.635 58 1.475

B2 89 2.593 62 1.463

B1 91 2.548 64 1.483

C2 92 2.832 63 1.478

C1 86 2.747 60 1.456

D2 100 2.963 60 1.425

D1 88 2.845 76 1.429

E3 94 2.956 65 1.493

E2 98 2.836 65 1.481 E1 86 2.788 61 1.449


TLD-600 TLD-700



A4 102 2.866 85 1.501

A3 99 2.956 79 1.516 A2 95 2.945 63 1.546 A1 122 2.706 65 1.544

C4 116 2.904 70 1.531

C3 105 3.257 72 1.511 C2 112 3.180 76 1.506 C1 126 3.092 73 1.478

E4 125 2.563 102 1.457

E2 103 2.602 74 1.526

F2 127 3.365 63 1.520

F1 102 3.354 62 1.536

H4 85 2.945 68 1.484

H3 103 3.134 74 1.436 H2 118 3.186 69 1.514 H1 114 2.943 62 1.507

CONCLUSIONS 38


TLD-600 TLD-700



A4 101 2.673 76 1.481

A3 106 2.904 81 1.402 A2 96 2.988 66 1.477 A1 109 2.932 63 1.510

C6 105 2.706 79 1.411

C5 103 2.955 85 1.451 C4 101 3.051 78 1.456 C3 103 3.129 61 1.453 C2 102 3.128 75 1.437 C1 101 2.868 67 1.467

E6 104 2.828 81 1.423

E5 116 2.956 72 1.411 E4 98 3.131 67 1.465 E3 124 3.154 65 1.434 E2 113 3.063 67 1.476 E1 99 3.026 62 1.463

F1 97 2.576 82 1.443

H1 126 3.089 66 1.410

I3 97 2.856 68 1.452

I2 100 3.216 64 1.455 I1 108 3.282 58 1,487

L6 86 2.713 73 1.400

L5 107 3.033 60 1.442 L4 102 3.093 65 1.448 L3 106 3.139 56 1.508 L2 87 3.114 54 1.439 L1 110 2.963 64 1.452

N5 119 2.982 67 1.463

N4 107 3.202 50 1.519 N3 114 3.254 68 1.444 N2 87 3.251 56 1.463 N1 113 2.901 71 1.466

CONCLUSIONS 39

TABLE 5.5. Absorbed dose and HTR determined from TLD-600 (6LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) measurements for MATROSHKA slice 15 (lung plane)

TLD-600 TLD-700



A5 80 2.755 63 1.471

A4 81 3.005 59 1.502 A3 88 3.050 55 1.493 A2 75 2.940 57 1.543 A1 95 2.405 61 1.504

C7 77 2.884 58 1.532

C6 91 3.022 52 1.483 C5 83 3.066 61 1.498 C4 90 3.158 50 1.529 C3 77 3.225 51 1.512 C2 78 3.180 53 1.524 C1 85 2.665 56 1.514

E7 86 2.986 55 1.519

E6 83 3.169 49 1.509 E5 77 3.280 54 1.466 E4 77 3.380 46 1.537 E3 80 3.348 58 1.460 E2 81 3.267 49 1.465 E1 86 3.076 51 1.469

H2 77 3.469 53 1.520

H1 81 3.254 51 1.509

I3 78 3.142 52 1.522

I2 83 3.408 49 1.486 I1 71 3.637 47 1.490

L3 76 2.857 52 1.506

L2 83 3.145 51 1.501 L1 78 3.177 54 1.500

N6 80 2.732 55 1.517

N5 81 3.120 54 1.503 N4 82 3.175 50 1.514 N3 95 3.271 50 1.512 N2 84 3.354 48 1.494 N1 95 3.212 54 1.554

CONCLUSIONS 40


TLD-600 TLD-700



A4 122 2.371 74 1.451

A3 127 2.588 77 1.444 A2 99 2.558 76 1.501 A1 132 2.406 78 1.463

C7 100 2.774 69 1.434

C6 93 3.067 63 1.482 C5 90 3.037 68 1.465 C4 109 3.123 69 1.469 C3 107 3.123 74 1.471 C2 96 3.076 61 1.511 C1 114 2.869 69 1.464

E8 97 2.920 65 1.535

E7 96 3.129 61 1.508 E6 100 3.353 68 1.463 E5 98 3.430 58 1.463 E4 106 3.469 63 1.482 E3 98 3.353 59 1.503 E2 87 3.201 58 1.495 E1 81 2.637 64 1.519

H3 110 3.464 59 1.468

H2 101 3.389 61 1.456 H1 94 2.842 69 1.484

I3 90 3.210 72 1.447

I2 94 3.459 52 1.508 I1 97 3.616 61 1.489

L7 93 2.832 59 1.504

L6 92 3.082 66 1.484 L5 98 3.285 67 1.477 L4 96 3.409 62 1.552 L3 110 3.232 58 1.483 L2 86 3.272 66 1.475 L1 104 3.144 65 1.413

N7 97 2.697 70 1.465

N6 97 3.090 61 1.540 N5 99 3.045 60 1.618 N4 101 3.203 63 1.468 N3 93 3.199 61 1.502 N2 94 3.130 65 1.485 N1 103 2.630 68 1.502

CONCLUSIONS 41


TLD-600 TLD-700



B7 93 2.858 54 1.470

B6 86 3.148 58 1.517 B5 80 3.240 54 1.426 B4 88 3.163 54 1.418 B3 84 3.132 59 1.487 B2 94 2.968 54 1.493 B1 88 2.543 58 1.491

D7 76 3.051 51 1.512

D6 76 3.539 61 1.461 D5 84 3.524 49 1.404 D4 87 3.604 46 1.452 D3 86 3.540 54 1.453 D2 91 3.444 50 1.473 D1 89 3.129 54 1.516

G2 80 3.557 54 1.474

G1 87 3.311 50 1.461

H3 77 3.164 51 1.463

H2 67 3.392 43 1.461 H1 90 3.543 44 1.425

K7 78 3.048 50 1.501

K6 77 3.237 48 1.469 K5 83 3.342 44 1.429 K4 75 3.495 45 1.476 K3 79 3.329 44 1.495 K2 72 3.152 51 1.465 K1 76 3.057 49 1.439

M6 83 2.803 57 1.465

M5 80 3.109 53 1.480 M4 99 3.081 60 1.500 M3 82 3.119 49 1.516 M2 96 3.077 55 1.470 M1 83 2.955 56 1.439

CONCLUSIONS 42


TLD-600 TLD-700



B6 90 2.978 50 1.483

B5 78 3.310 49 1.475 B4 72 3.368 47 1.460 B3 70 3.512 49 1.485 B2 77 3.344 45 1.439 B1 88 2.924 52 1.512

D7 77 3.130 56 1.460

D6 68 3.583 43 1.480 D5 73 3.609 38 1.477 D4 76 3.690 42 1.473 D3 86 3.571 43 1.515 D2 76 3.475 49 1.492 D1 79 2.899 48 1.487

G2 75 3.583 49 1.421

G1 84 3.221 45 1.471

H3 69 3.284 53 1.452

H2 90 3.455 40 1.464 H1 85 3.660 45 1.461

K7 65 3.182 52 1.433

K6 86 3.514 43 1.493 K5 84 3.586 46 1.464 K4 91 3.567 46 1.450 K3 92 3.439 52 1.425 K2 72 3.093 51 1.472 K1 79 2.749 54 1.439

M6 90 2.668 56 1.500

M5 82 3.076 63 1.466 M4 82 3.251 52 1.445 M3 77 3.330 51 1.453 M2 79 3.081 52 1.546 M1 75 2.705 54 1.457

CONCLUSIONS 43


TLD-600 TLD-700



B6 89 2.715 57 1.387

B5 73 3.129 54 1.468 B4 75 3.285 47 1.455 B3 72 3.406 56 1.483 B2 100 3.162 48 1.457 B1 84 2.947 61 1.476

D7 83 3.079 50 1.462

D6 67 3.624 54 1.436 D5 82 3.623 41 1.467 D4 90 3.609 46 1.450 D3 74 3.600 43 1.456 D2 71 3.372 45 1.471 D1 84 2.983 49 1.449

G2 83 3.598 45 1.475

G1 80 3.107 49 1.468

H3 69 3.184 45 1.505

H2 74 3.463 57 1.444 H1 73 3.595 43 1.448

K7 84 2.979 50 1.476

K6 83 3.298 55 1.389 K5 73 3.623 49 1.409 K4 79 3.555 41 1.466 K3 83 3.420 45 1.472 K2 81 3.311 46 1.475 K1 80 2.833 50 1.499

M4 79 2.981 54 1.510

M3 78 3.127 55 1.504 M2 75 3.089 49 1.483 M1 87 2.955 55 1.466

CONCLUSIONS 44


TLD-600 TLD-700



B6 85 2.935 55 1.465

B5 80 3.312 49 1.636 B4 67 3.563 43 1.500 B3 86 3.284 51 1.534 B2 81 3.186 57 1.467 B1 87 2.731 59 1.539

D7 88 3.222 53 1.498

D6 87 3.460 50 1.456 D5 81 3.701 50 1.451 D4 86 3.651 45 1.452 D3 75 3.625 45 1.742 D2 84 3.419 48 1.530 D1 76 2.975 54 1.519

G2 78 3.729 47 1.545

G1 81 3.211 48 1.497

H3 73 3.253 47 1.523

H2 79 3.550 44 1.490 H1 73 3.754 47 1.486

K7 81 3.212 52 1.516

K6 85 3.445 49 1.457 K5 75 3.796 46 1.516 K4 79 3.818 46 1,496 K3 78 3.592 46 1.482 K2 79 3.389 49 1.507 K1 88 2.669 49 1.524

M4 77 2.942 55 1.510

M3 80 3.000 53 1.504 M2 83 2.947 51 1.503 M1 81 2.808 53 1.671

CONCLUSIONS 45

TABLE 5.11. Absorbed dose and HTR determined from TLD-600 (6LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) measurements for MATROSHKA slice 27 (intestine plane)

TLD-600 TLD-700



B6 116 2.998 80 1.478

B5 104 3.202 68 1.425 B4 101 3.478 61 1.454 B3 86 3.269 70 1.476 B2 89 3.024 55 1.491 B1 89 2.463 67 1.490

D7 94 3.398 74 1.431

D6 80 3.622 61 1.498 D5 111 3.680 58 1.430 D4 113 3.534 61 1.398 D3 112 3.539 70 1.444 D2 111 3.534 55 1.475 D1 105 2.816 64 1.501

F5 103 2.584 73 1.438

F3 113 2.696 67 1.437 F1 124 2.682 73 1.428

H2 106 3.541 55 1,.417

H1 107 3.067 61 1.471

I3 104 3.257 60 1.471

I2 85 3.719 52 1.479 I1 107 3.697 61 1.413

L4 115 3.243 73 1.472

L3 103 3.605 60 1.440 L2 95 3.736 57 1.476 L1 104 3.538 58 1.495

N4 128 2.863 80 1.482

N3 93 3.062 79 1.468 N2 110 2.850 73 1.485 N1 101 2.605 63 1.489

CONCLUSIONS 46


TLD-600 TLD-700



B7 75 2.858 53 1.494

B6 84 3.312 49 1.449 B5 72 3.589 45 1.463 B4 72 3.547 40 1.479 B3 77 3.590 45 1.498 B2 75 3.313 45 1.469 B1 76 2.843 54 1.472

D8 72 3.102 53 1.463

D7 76 3.547 45 1.475 D6 74 3.760 41 1.486 D5 69 3.839 40 1.477 D4 84 3.879 41 1.456 D3 73 3.818 41 1.517 D2 73 3.474 42 1.459 D1 77 2.822 51 1.474

G2 70 3.755 44 1.451

G1 73 3.015 44 1.447

H4 68 3.005 50 1.477

H3 68 3.579 41 1.457 H2 76 3.736 40 1.462 H1 69 3.866 40 1.465

K7 80 3.070 56 1.442

K6 87 3.437 43 1.432 K5 80 3.844 48 1.446 K4 77 3.918 52 1.457 K3 81 3.717 40 1.530 K2 78 3.599 43 1.482 K1 77 3.253 53 1.211

M5 82 2.925 53 1.460

M4 87 3.230 52 1.467 M3 95 3.318 49 1.513 M2 101 3.241 56 1.487 M1 86 2.809 55 1.443

CONCLUSIONS 47


TLD-600 TLD-700



A3 67 2,759 59 1,456

A2 69 2,801 53 1,504 A1 85 2,659 53 1,482

C7 82 3,128 49 1,445

C6 86 3,515 46 1,464 C5 83 3,686 54 1,430 C4 63 3,853 41 1,501 C3 72 3,739 38 1,490 C2 82 3,523 44 1,458 C1 82 3,036 54 1,477

E8 na na na na

E7 86 3,232 48 1,410 E6 72 3,655 44 1,496 E5 64 3,933 42 1,440 E4 67 3,919 34 1,487 E3 76 3,918 43 1,423 E2 76 3,869 39 1,543 E1 75 3,538 43 1,438

H2 68 3,689 40 1,429

H1 70 3,082 47 1,466

I4 92 3,114 58 1,458

I3 51 3,632 56 1,479 I2 66 3,843 37 1,437 I1 70 3,971 40 1,458

L7 89 3,401 56 1,499

L6 90 3,674 54 1,470 L5 94 3,727 54 1,492 L4 90 3,776 55 1,504 L3 101 3,888 52 1,481 L2 92 3,766 50 1,489 L1 89 3,432 56 1,490

N5 97 3,240 55 1,515

N4 103 3,379 56 1,494 N3 95 3,583 51 1,510 N2 102 3,421 58 1,524 N1 98 3,065 58 1,466

CONCLUSIONS 48


TLD-600 TLD-700



A5 79 2.480 63 1.423

A4 80 2.746 57 1.419 A3 76 2.745 54 1.485 A2 72 2.717 52 1.478 A1 95 2.249 56 1.464

C7 68 3.000 60 1.449

C6 88 3.120 48 1.532 C5 84 3.172 51 1.441 C4 75 3.095 48 1.458 C3 81 2.970 61 1.459 C2 91 3.076 57 1.468 C1 88 2.807 54 1.486

E7 75 2.954 58 1.465

E6 80 3.127 51 1.434 E5 72 3.338 50 1.464 E4 85 3.111 48 1.448 E3 78 2.967 49 1.438 E2 78 2.937 49 1.451 E1 74 2.915 49 1.478

F1 76 2.821 47 1.467

H4 80 2.786 46 1.488

H3 69 3.264 57 1.407 H2 75 3.390 54 1.437 H1 78 3.001 45 1.508

K7 93 2.993 59 1.475

K6 95 3.175 53 1.449 K5 67 3.157 57 1.452 K4 75 3.180 42 1.439 K3 93 3.191 43 1.453 K2 87 3.145 49 1.422 K1 80 2.956 56 1.465

M7 102 2.588 61 1.461

M6 85 3.027 51 1.461 M5 81 3.085 52 1.454 M4 90 3.054 60 1.460 M3 89 3.094 61 1.394 M2 77 2.939 53 1.459 M1 83 2.500 50 1.506

CONCLUSIONS 49

FIG. 5.5. Illustration of the MATROSHKA coordinate system used in the three-dimensional dose plots.

FIG. 5.6. Depth dose distribution measured with TLDs for the MATROSHKA phantom slice 3.


CONCLUSIONS 50




CONCLUSIONS 51




CONCLUSIONS 52




CONCLUSIONS 53




CONCLUSIONS 54

The dose distribution within the phantom torso is further discussed for two AP section planes (Figure 5.20) at different lateral distances from the central rod. From the plots in Figures 5.21 and 5.22 for the planes y = −38.1 mm and y = 12.7 mm, the dose gradients from head to abdomen and with increasing depth of the body are evident. The gradients are explained by the phantom’s self-attenuation and shielding by the ISS hull. However, the distributions are not symmetric around the x = 0 plane of the central rod.

The HTR for TLD-700 for the y = −38.1 mm and the y = 12.7 mm

plane closer to the central rod, the HTR distribution is practically flat. This effect indicates continuous radiobiological effectiveness of the particle and energy spectra. Variations are assumed to be due to statistical effects only. The distribution of HTR for neutron-sensitive TLD-600 detectors increases significantly with the depth of the body and, thus, indicates enhanced generation of thermal neutrons.

FIG. 5.20. Illustration of an AP section through the MATROSHKA torso (courtesy DLR).

CONCLUSIONS 55

FIG. 5.21. Absorbed dose distribution for the AP section y = −38.1 mm of slices 3, 25 and 29. Data points were fitted by quadratic polynomials.

FIG. 5.22. Absorbed dose distribution for the AP section y = 12.7 mm of slices 3, 25 and 29. Data points were fitted by quadratic polynomials.

5.2 ORGAN ABSORBED DOSES Absorbed doses measured in five detector boxes at the place of the eye, the lungs, the stomach, the kidney and the intestine are tabulated in Tables 5.15 and 5.16. Different types of TL phosphors from ATI were accommodated in these boxes (see Appendix A): four chips each of 6LiF:Mg,Ti (TLD-600) and 7LiF:Mg,Ti (TLD-700) as well as three chips of CaF2:Tm (TLD-300). The given uncertainties correspond to two standard deviations (2 σ) or a 95 % confidence level. The doses contained in the Tables have not been corrected for TL efficiency for this allows revealing important information about the properties of the radiation field. In accordance with the general trend known from the detector tubes dispersed in the torso, the highest dose was absorbed in the eye, the lowest in the kidney. Analyzing the behaviour of the HTR for TLD-600, an increase in neutron production towards the lower body parts was

CONCLUSIONS 56

found with the exception of the intestine which seems to indicate a decreasing neutron level. This might be caused by a homogenous radiation field around the torso. An additional sixth detector package was exposed atop the head. The measured dose was higher by ~40% compared with the dose to the kidney.

An important aspect lies in the fact that no organ was exposed disproportionately high, nor did the organ absorbed dose essentially exceed the dose to the skin. This could not necessarily be presumed as the creation of secondary particles and target fragments plays an essential role. It thus becomes evident that the skin dose may be used as a conservative estimate for the whole-body exposure. The measured organ doses—along with the LET spectra determined with PNTD—provide a valuable base for risk estimates related to human space exploration.

In contrast to TLD-700 for which TL efficiency decreases rapidly with LET, the relative efficiency of CaF2:Tm (TLD-300) is much closer to unity—even for very high LET (Figure 4.11). It is therefore assumed that the doses determined with TLD-300 do not require efficiency correction which is estimated to be within the statistical uncertainty. The high dose of 93 ±18 mGy atop the head is related to low-energy bremsstrahlung components (Figure 4.16). Comparison of doses from TLD-300 and TLD-700 otherwise verifies the ~12 % overresponse of TLD-700. TABLE 5.15. Absorbed dose and HTR determined from TLD-600 (6LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) measurements for MATROSHKA organ dose boxes (NTDP)

TLD-600 TLD-700

Organ Absorbed dose (mGy) HTR


Eye 85 ± 10 2.742 ± 0.254 77 ± 20 1.453 ± 0.060

Lungs 82 ± 14 2.919 ± 0.018 75 ± 2 1.446 ± 0.060

Stomach 80 ± 24 2.756 ± 0.232 63 ± 6 1.446 ± 0.024

Kidney 81± 2 3.002 ± 0.222 64 ± 6 1.461 ± 0.030

Intestine 85 ± 10 2.864 ± 0.194 66 ± 18 1.432 ± 0.036

Head 87 ± 14 1.836 ± 0.096 84 ± 20 1.464 ± 0.036

TABLE 5.16. Absorbed dose determined from TLD-300 (CaF2:Tm) measurements for MATROSHKA organ dose boxes (NTDP)

TLD-300

Organ Absorbed dose (mGy)

Eye 84 ± 20

Lungs 70 ± 26

Stomach 74 ± 20

Kidney 63 ± 4

Intestine 65 ± 16

Head 93 ± 18

CONCLUSIONS 57

5.3 PONCHO ABSORBED DOSES Skin doses were measured on the anterior, posterior and lateral sides of the torso. The detectors were housed in polyethylene boxes sued to the phantom surface and located at the mid thorax (box 1), the upper abdomen (box 2), the lateral right (box 3) and left sides (box 4), the mid dorsal (box 5) and the lumbar spine (box 6). The self-attenuation of the detector boxes causes the actual skin doses to be higher by roughly a factor of 2. A continuous skin dose distribution was derived from the various dosimeter positions on the poncho. The contribution of thermal neutrons is slightly enhanced but continuous as well as can be inferred from the different HTR measured in TLD-600 and TLD-700 detectors. Shielding thickness directly affects neutron moderation. TABLE 5.17. Absorbed dose and HTR determined from TLD-600 (6LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) measurements for MATROSHKA poncho detector boxes

TLD-600 TLD-700

Poncho Absorbed dose (mGy) HTR


Box 1 97 ± 22 1.911 ± 0.152 83 ± 10 1.459 ± 0.062

Box 2 90 ± 16 1.889 ± 0.144 88 ± 14 1.448 ± 0.092

Box 3 99 ± 30 1.948 ± 0.072 87 ± 16 1.464 ± 0.028

Box 4 89 ± 6 1.993 ± 0.058 76 ± 10 1.478 ± 0.052

Box 5 87 ± 8 1.962 ± 0.062 77 ± 14 1.511 ± 0.040

Box 6 92 ± 16 1.908 ± 0.076 81 ± 8 1.500 ± 0.080

TABLE 5.18. Absorbed dose determined from TLD-300 (CaF2:Tm) measurements for MATROSHKA poncho detector boxes

TLD-300

Poncho Absorbed dose (mGy)

Box 1 102 ± 18

Box 2 95 ± 12

Box 3 92 ± 20

Box 4 102 ± 42

Box 5 106 ± 24

Box 6 94 ± 40

5.4 REFERENCE DETECTOR SETS Reference detector packages from all participating laboratories were stored inside the ISS over the course of the experiment. The measured doses (Table 5.19) confirmed the initial impression of particularly low dose rates. However, information about where exactly the detector sets have been mounted (panel no.) has not yet been released by ESA or Roskosmos.

CONCLUSIONS 58

TABLE 5.19. Absorbed dose determined from TLD-300 (CaF2:Tm), TLD-600 (6LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) measurements for reference sets

TLD-300 TLD-600 TLD-700

Reference Absorbed dose (mGy)

Absorbed dose (mGy)

Absorbed dose (mGy)

Set 1 108 ± 10 128 ± 14 102 ± 18

Set 2 110 ± 18 123 ± 26 101 ± 28

6 DATA INTERCOMPARISON 6.1 INTERCOMPARISON MATROSHKA-II PHASE A

VERSUS MATROSHKA-I For the purpose of analysing the difference between radiation exposure during an EVA compared to that of a stay inside the ISS and thus being able to examine the biological hazards a detailed intercomparison of the obtained dose rates of Organ Dose Packages and Poncho is presented (Table 6.1). TABLE 6.1. Organs and Poncho Matroshka-II Phase A vs. Matroshka I

MATROSHKA-I = 100% TLD-600 TLD-700

Dose (mGy/d)

Error (mGy/d)

Dose (%)

Dose (mGy/d)

Error (mGy/d)

Dose (%)

NTDP #1 -0.055 0.013 82.143 -0.083 0.029 73.296

NTDP #2 -0.034 0.023 87.743 -0.022 0.010 90.946

NTDP #3 -0.042 0.031 85.026 -0.043 0.014 81.287

NTDP #4 -0.026 0.010 90.306 -0.045 0.010 80.623

NTDP #5 -0.003 0.018 98.931 -0.014 0.025 93.514

NTDP #6 -0.225 0.033 53.359 -0.242 0.028 50.638

Dose (mGy/d)

Error (mGy/d)

Dose (%)

Dose (mGy/d)

Error (mGy/d)

Dose (%)

Poncho #1 -0.424 0.043 40.399 -0.377 0.031 39.441

Poncho #2 -0.344 0.065 43.627 -0.293 0.035 47.012

Poncho #3 -0.228 0.041 56.202 -0.202 0.022 56.058

Poncho #4 -0.288 0.015 47.789 -0.258 0.019 46.502

Poncho #5 -0.323 0.040 44.324 -0.254 0.022 47.298

Poncho #6 -0.255 0.042 51.666 -0.277 0.021 51.348 First analysis shows that doses accumulated in the eye, lung, stomach intestine and kidney decreased between ~1% (intestine) and ~20% (eye) which indicates that the Russian Zevzda Module provides better shielding especially for the upper regions of the torso. Furthermore it has to be noted that the highest decline occurred for the head detector package. Generally a more homogenous radiation environment inside the ISS can be assumed (Figures 6.1-6.2).

DATA INTERCOMPARISON 60

FIG. 6.1. MATROSHKA data intercomparison among TL dosemeters for organ dose boxes TLD-600

FIG. 6.2. MATROSHKA data intercomparison among TL dosemeters for organ dose boxes TLD-700

Poncho doses are reduced by a factor ~2 and show a similar trend towards a more even radiation distribution thus confirming the previous statement (Figure 6.3-6.4).


FIG. 6.3. MATROSHKA data intercomparison among TL dosemeters for poncho TLD-600

FIG. 6.4. MATROSHKA data intercomparison among TL dosemeters for poncho TLD-700

The enhanced contribution of thermal neutrons in the hull of the ISS can be verified as shown in Figure 6.5.- 6.8. The analysis shows that thermal neutron contribution is significantly increased in the Organs whereas a slight increase can be seen for the skin dose i.e. the Poncho.


FIG. 6.5. MATROSHKA data intercomparison organ dose boxes HTR values TLD-600

FIG. 6.6. MATROSHKA data intercomparison organ dose boxes HTR values TLD-700

FIG. 6.7. MATROSHKA data intercomparison poncho HTR values TLD-600


FIG. 6.8. MATROSHKA data intercomparison poncho HTR values TLD-700

6.2 INTERNATIONAL INTERCOMPARISON The German Aerospace Center (DLR) as the principal investigator of the MATROSHKA programme stimulated data intercomparison between all laboratories having applied passive dosimetry. In a first step, the doses measured for the six organ detector boxes were collected from the participants. During the 12th Workshop on Radiation Monitoring for the International Space Station (WRMISS)—held from September 10 to 12 2007 in Stillwater, USA—the final data analysis was presented. As can be seen from Figures 6.9 to 6.14, the results from ATI mostly were in good agreement with those of the other groups.

FIG. 6.9. MATROSHKA data intercomparison among TL dosemeters for the eye detector box.


FIG. 6.10. MATROSHKA data intercomparison among TL dosemeters for the lung detector box.

FIG. 6.11. MATROSHKA data intercomparison among TL dosemeters for the stomach detector box.

FIG. 6.12. MATROSHKA data intercomparison among TL dosemeters for the kidney detector box.


FIG. 6.13. MATROSHKA data intercomparison among TL dosemeters for the intestine detector box.

FIG. 6.14. MATROSHKA data intercomparison among TL dosemeters for the top-head detector box.

7 CONCLUSIONS The ESA MATROSHKA-II phase A experiment was aimed to simulate an astronaut’s body during an inside stay onboard the ISS. The phantom body was equipped with more than 6000 passive detectors in a regular grid and launched to the ISS with a Russian Progress freighter December 21 2005. Cooperation of 18 laboratories around the world—among them the leading space-faring nations—made it the most extensive research effort in space radiation dosimetry performed so far. MATROSHKA was installed inside the Russian Segment (Zvezda) on January 5 2006 and recovered on December 7 2006.

During that 11-month period, the integrated passive radiation detectors measured absorbed doses within the anthropomorphic phantom torso, particularly in radiosensitive organs and tissues. Intercomparison of MATROSHKA-II phase A versus MATROSHKA-I of the obtained results revealed a less steep gradient from the head to the abdomen therefore a more continuous radiation environment inside the ISS than during an EVA is plausible. In the depth of the body a similar dose gradient was obtained. Furthermore a significant reduction of absorbed doses to the skin and head was found. The significant neutron component originated from fragmentation processes and the spacecraft shielding. Due to efficient moderation within tissue the contribution of thermal neutrons was found to increase with depth. The doses to selected organs (eye, lung, stomach, kidney, intestine) were below the dose at the surface implying that the skin dose can be regarded as conservative estimate for whole-body exposure to cosmic rays. Thermal neutron generation also increases within the spacecraft.

The results are expected to contribute essentially to reliable radiation

risk estimations for astronaut crews.

The MATROSHKA-II experiment is currently being continued in the frame of phase B. The phantom is exposed without containment inside the Zvezda Module. Upload of phase B equipment is scheduled for March 9 2007 (Soyuz-14S). During this phase both active and passive detectors shall be exposed inside the Station for a period of 6 to 9 months. A third phase to study the effects of the solar cycle is discussed between the relevant space authorities.

8 PUBLICATIONS The results from the MATROSHKA-I experiment have already been presented in lectures and posters at national and international conferences and will be published in renowned scientific journals, such as RADIATION PROTECTION DOSIMETRY. • Hajek M, Bergmann R, Vana N, Fugger M, Fürweger C. Radiation

exposure of astronaut crew during space walks (MATROSHKA I) – selected Austrian results. 10th Symposium on Neutron Dosimetry; 2006 Jun 12–16; Uppsala, Sweden. Oxford: Oxford University Press. In press 2006.

• Hajek M, Bergmann R, Fugger M, Vana N. Austrian results from the

MATROSHKA I experiment. 11th Workshop on Radiation Monitoring for the International Space Station; 2006 Sept 6–8; Oxford, UK.

• Hajek M, Bergmann R, Fugger M, Vana N. Radiation exposure of

astronaut crew during space walks. 56th Annual Meeting of the Austrian Physical Society; 2006 Sept 18–21; Graz, Austria.

The results from the MATROSHKA-II phase A experiment will be presented in depth at upcoming national and international conferences. Various publications are planned in renowned scientific journals. It was further agreed to dedicate a special issue of the journals RADIATION MEASUREMENTS or RADIATION RESEARCH to the scientific outcome of the MATROSHKA project, with concise contributions from all participating laboratories. The MATROSHKA-II research effort is going to be continued in the frame of Phase B. In a third step, the influence of solar activity variation shall be examined by means of a second outside exposure. Upon completion of these tasks, a summary paper shall be submitted to NATURE on behalf of all investigators.

APPENDIX A

FIG. A.1. Distribution of detector tubes within the MATROSHKA phantom slice 3; cut-outs for integration of the eye organ box and a SSD (courtesy DLR).

APPENDIX A 69

FIG. A.2. Distribution of detector tubes within the MATROSHKA phantom slice 7 (courtesy DLR).


APPENDIX A 70


APPENDIX A 71

FIG. A.5. Distribution of detector tubes within the MATROSHKA phantom slice 15; cut-outs for integration of the lung organ box and a SSD (courtesy DLR).

APPENDIX A 72


APPENDIX A 73


APPENDIX A 74


APPENDIX A 75


APPENDIX A 76


APPENDIX A 77

FIG. A.11. Distribution of detector tubes within the MATROSHKA phantom slice 27; cut-outs for integration of the intestine organ box and a SSD (courtesy DLR).

APPENDIX A 78


APPENDIX A 79


APPENDIX A 80


APPENDIX A 81

FIG. A.15. TL detector distribution for MATROSHKA eye organ box in slice 3 (courtesy DLR).

FIG. A.16. TL detector distribution for MATROSHKA lung organ box in slice 15 (courtesy DLR).

FIG. A.17. TL detector distribution for MATROSHKA stomach organ box in slice 20 (courtesy DLR).

FIG. A.18. TL detector distribution for MATROSHKA kidney organ box in slice 22 (courtesy DLR).

FIG. A.19. TL detector distribution for MATROSHKA intestine organ box in slice 27 (courtesy DLR).

FIG. A.20. TL detector distribution for MATROSHKA detector box on top of the head (courtesy DLR).

APPENDIX A 82

FIG. A.21. TL detector distribution for MATROSHKA poncho detector box 1 (courtesy DLR).






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