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Advances in Space Research 34 (2004) 1414–1419

Austrian dose measurements onboard space station MIR andthe International Space Station – overview and comparison

T. Berger a,*, M. Hajek a, L. Summerer a, N. Vana a, Y. Akatov b, V. Shurshakov b,V. Arkhangelsky b

a Atominstitute of the Austrian Universities, Stadionallee 2, 1020 Vienna, Austriab Institute for Biomedical Problems, 76-A Khoroshevskoe sh., 123007 Moscow, Russia

Received 13 October 2002; received in revised form 14 August 2003; accepted 14 August 2003

Abstract

The Atominstitute of the Austrian Universities has conducted various space research missions in the last 12 years in cooperation

with the Institute for Biomedical Problems in Moscow. They dealt with the exact determination of the radiation hazards for cos-

monauts and the development of precise measurement devices. Special emphasis will be laid on the last experiment on space station

MIR the goal of which was the determination of the depth distribution of absorbed dose and dose equivalent in a water filled

Phantom. The first results from dose measurements onboard the International Space Station (ISS) will also be discussed. The

spherical Phantom with a diameter of 35 cm was developed at the Institute for Biomedical Problems and had 4 channels where

dosemeters can be exposed in different depths. The exposure period covered the timeframe from May 1997 to February 1999.

Thermoluminescent dosemeters (TLDs) were exposed inside the Phantom, either parallel or perpendicular to the hull of the

spacecraft. For the evaluation of the linear energy transfer (LET), the high temperature ratio (HTR) method was applied. Based on

this method a mean quality factor and, subsequently, the dose equivalent is calculated according to the Q(LET1) relationship

proposed in ICRP 26. An increased contribution of neutrons could be detected inside the Phantom. However the total dose

equivalent did not increase over the depth of the Phantom. As the first Austrian measurements on the ISS dosemeter packages were

exposed for 248 days, starting in February 2001 at six different locations onboard the ISS. The Austrian dosemeter sets for this first

exposure on the ISS contained five different kinds of passive thermoluminescent dosemeters. First results showed a position de-

pendent absorbed dose rate at the ISS.

� 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Keywords: Radiation dose; MIR; International Space Station; Thermoluminescent dosemeters

1. Introduction

The recently established International Space Station

(ISS) and the associated increased number of extrave-

hicular activities (EVAs) in free space necessitates theaccurate determination of the dose equivalent load on

astro- and cosmonauts. Interaction of the primary cos-

mic radiation environment, which consists mostly of

protons, electrons and heavy charged particles (HCP),

with the hull of the spacecraft results in the production of

a complex secondary radiation field including addition-

* Corresponding author. Tel.: +43-1-58801-14193; fax: +43-1-58801-

14199.

E-mail address: tberger@ati.ac.at (T. Berger).

0273-1177/$30 � 2004 COSPAR. Published by Elsevier Ltd. All rights reser

doi:10.1016/j.asr.2003.08.063

ally neutrons, photons, muons and pions. The detailed

energy and particle spectra inside the spacecraft strongly

depend on the different shielding masses and the orbit

parameters. For practical radiation protection purposes

it should be analyzed whether the skin dose can beapplied for a conservative estimation of radiation risk

factors for the astronauts. Measurements inside tissue-

equivalent Phantoms are essential in order to solve this

complex task and to obtain a better knowledge of the

dose distribution inside the human body. Up to now,

only three space experiments (Konradi et al., 1992;

Yasuda, 2000; Badhwar et al., 2002) dealt with the de-

termination of the depth dose profile inside tissue-equivalent Phantom. The results obtained in the project

Phantom are the first measurement of depth dose profiles

ved.

T. Berger et al. / Advances in Space Research 34 (2004) 1414–1419 1415

during a long period of time onboard a space station. The

increased interest in Phantom measurements can also be

seen by the newly planned ESA and Russian projects

MATROSHKA and MATROSHKA R were Phantom

torsos will be positioned outside and inside the ISS.

Table 1

Positions of the Phantom inside space station MIR and duration of the

Phantom project phases

Phantom Timeframe Phantom

exposure (d)

Position

Phase 1 May 1997–

February 1998

271 Commander Cabin

Phase 2 May 1998–

August 1998

99 Board Engineer

Cabin

15 Board Engineer

Cabin

Phase 3 August 1998–

February 1999

170 Module Kwant 2

2. Instruments and methods

For all Austrian dose measurements on MIR and the

ISS the data were collected using passive Thermolumi-

nescent dosemeters (TLDs) of different types. The

dosemeters were pre irradiated and selected in groups

depending on their gamma efficiency prior to all flights.Each TL-chip was calibrated individually in the field of

a 60Co – gamma source. Calibration was performed in

terms of absorbed dose in water. Read out was per-

formed with the TL-DAT II read out system manufac-

tured at the Atominstitute of the Austrian Universities.

This system can heat up to 480 �C with an adjustable

heating rate. After readout post flight calibrations were

performed and the obtained data were corrected for theambient background dose. No efficiency correction was

applied for the TLDs but investigations concerning the

efficiency of various TLD materials are currently un-

dertaken (Berger, 2003). TLDs are commonly used just

for the determination of the absorbed dose. By using

various TLD types (6LiF:Mg,Ti – TLD 600 and 7LiF:

Mg,Ti – TLD 700) information can also be gathered

about the neutron dose (extended pair method) and theaverage quality factor and thus the dose equivalent

(HTR method) in a mixed radiation field.

2.1. HTR method

For the further analysis of TLD data, the HTR

method developed at the Atominstitute of the Austrian

Universities was used. The method was already appliedsuccessfully during several space missions including

measurements onboard space station MIR by Vana

et al. (1999), space shuttles (Badhwar, 1996) and bio-

satellites (Vana, 1996). It utilizes the well known differ-

ent LET – efficiencies of the high temperature peaks

relative to the main peak 5 of LiF:Mg,Ti glowcurves.

The high temperature ratio (HTR) is defined as the ratio

between the high temperature emission after exposure ina radiation field of unknown composition and the

emission in the same temperature region after 60Co –

gamma irradiation, normalized on the peak 5 height, i.e.

the same absorbed dose, of a specific TL-chip. A HTR

vs. LET calibration curve was recorded by exposure in

various reference radiation fields (Sch€oner, 1999). Re-

cent irradiations in order to refine the established cali-

bration function were conducted at the NationalInstitute of Radiological Sciences (NIRS), Chiba, Ja-

pan, using various ion beams with LET values up to 400

keV/lm (Berger, 2003). From the ‘‘averaged’’ LET de-

termined according to this functional relationship the

mean quality factor and, subsequently, the dose equiv-

alent is calculated based on the Q(LET1) relation pro-

posed in ICRP 26.

2.2. Extended pair method

Using the difference in the main dosimetric peak 5

readings of 6LiF and 7LiF glowcurves information

about the thermal and epithermal neutrons can be

achieved (pair method). This is due to the different

neutron cross sections for 6Li and 7Li. This pair method

is commonly used for evaluation of thermal neutrondose (Horowitz, 1981) after calibration of the TLDs in a

thermal neutron field. Based on a calibration in the

CERF neutron reference field at CERN (Mitaroff, 2002)

which reassembles the neutron radiation spectra at high

altitudes the pair method was extended and used for the

determination of the neutron dose equivalent in aircraft

(Hajek, 2002) and in space.

2.3. Project Phantom on MIR

The Institute for Biomedical Problems developed a

water-filled Phantom with a diameter of 35 cm, con-

sisting of four channels positioned in one plane per-

pendicular to each other. In these channels, dosimeters

of the types TLD 600 and TLD 700 were exposed in

different depths. Due to their small dimensions of6� 6� 0.9 mm3, TLDs are perfectly appropriate devices

for such conditions. Table 1 gives the location of the

Phantom inside the station and the timeframe of the

project phases.

The exposure times ranged from 99 to 271 days.

During the project phases 1 and 2, dosimeter packages

(4�TLD 600, 4�TLD 700 each) were exposed in six

different depths in the channels number 2 and 4 per-pendicular to the hull of the spacecraft. In phase 3, the

exposition took place in three different depths in chan-

nels number 1 and 3 parallel to the hull of the space

stationMIR (Fig. 1). The three positions of the Phantom

Fig. 1. Channel layout of the Phantom onboard space station MIR.

1416 T. Berger et al. / Advances in Space Research 34 (2004) 1414–1419

onboard the space station and the various exposure

locations of the dosimeters inside the Phantom enabled

the measurement of the depth distribution of absorbed

dose and ‘‘averaged’’ LET under various shielding con-

ditions. The exposure period from May 1997 to Febru-ary 1999 corresponded to increasing activity of the 23rd

solar cycle. The data obtained with the passive thermo-

luminescent dosemeters are consequently understood as

mean values at different exposure locations over the long

duration of each project phase (3–9 months). Back-

ground packages were stored in Moscow for the time-

frame of the exposure in space.

2.4. Project RBO-2 on ISS

In cooperation with the Institute for Biomedical

Problems in Moscow, the Project RBO-2 was started in

February 2001. In the framework of the project two long

term exposures of six passive dosemeter sets are plan-

ned. The sets are exposed in the Russian Segment of the

ISS. The first exposure was carried out between Febru-ary and November 2001. The overall time of the expo-

sure was 248 days. The second dosemeter packages are

currently onboard the ISS and will be returned to earth

at the end of the year 2002. The overall goal of the

project is to measure the radiation load at six fixed

points of the ISS over a long period of time. Table 2

gives the positions of the dosemeter packages for part

Table 2

Dosemeter positions onboard the ISS

Dosemeter

packages

Location onboard the ISS

A11 Cabin of the RS ISS starboard (right side) near the

window

A12 Cabin of the RS ISS port (left side) near the

window

A13/A16/A17 Core block RS ISS by the central axis, on the

floor, near window No. 6

A14 Core block RS ISS, toilet

A15 Core block RS ISS by the central axis, on the

ceiling

one of the project. From the Austrian side five different

types of TLDs were used. These were the commonly

available TLD 600, TLD 700, TLD 700H, TLD 300 and

TLD 200.

3. Results and discussion

The data for the project Phantom and the first mea-

surements on the Russian module of the ISS will be

presented and discussed in the following section.

3.1. Project Phantom on MIR

Fig. 2 displays a three dimension plot of the sum-

marized results for the depth distribution of absorbed

dose for the project phases 2 and 3. A stronger decrease

in absorbed depth dose rate is observed for the phases 1

and 2. This is related to the position of these dosemeters

in channel number 2 perpendicular to the hull of the

spacecraft (see also Fig. 1). For these two phases, the

absorbed dose rates for both the TLD 600 and the TLD700 dosemeters are almost independent of the location

of the Phantom. The absorbed dose rate for phase 3,

during which the Phantom was located in Module

Kwant 2 and the dosemeters were exposed parallel to

the spacecraft hull (channels 1 and 3), is lower for all

measured data points. This observed lower dose rate can

be explained by an increased shielding thickness (some

additional 5 g/cm2) in the Kwant 2 Module. The highershielding in this module results also in a greater differ-

ence in the TLD 600 and TLD 700 absorbed dose rates

due to a higher contribution of neutrons. Based on the

evaluated high temperature ratio the ‘‘averaged’’ LET

Fig. 2. Depth distribution of absorbed dose rate for the Phantom

phases 2 (channels 2/4) and 3 (channels 1/3) measured with TLD 700.

Fig. 3. Depth distribution of dose equivalent rate for the Phantom

phases 2 (channels 2/4) and 3 (channels 1/3) measured with TLD 700.

T. Berger et al. / Advances in Space Research 34 (2004) 1414–1419 1417

and, subsequently, the dose equivalent rate were evalu-

ated by means of the HTR method. The HTR for the

TLD 700 does not change significantly over the whole

depth of the Phantom. In contrast, the HTR for the

TLD 600 increases due to an increasing contribution of

neutrons inside the Phantom.

Figs. 2 and 3 show the absorbed dose and the dose

equivalent rates for the phases 2 and 3 measured by

Table 3

Absorbed dose rates for TLD 200, TLD 300 and TLD 700H

Position TLD 200 TLD 300

Absorbed dose

rate (lGy/d)

r (%) Absorbed d

rate (lGy/d

A11 261 1.2 289

A12 228 2.7 258

A13 211 2.2 230

A14 174 1.9 183

A15 171 1.2 182

A16 241 1.6 247

A17 231 1.0 233

Table 4

Absorbed dose rates for TLD 600 and TLD 700

Position TLD 600 TLD 700

Absorbed dose

rate (lGy/d)

r (%) Absorbed do

rate (lGy/d)

A11 301 1.4 292

A12 259 4.1 247

A13 247 0.9 239

A14 209 1.2 200

A15 210 6.4 198

A16 275 1.4 265

A17 266 1.8 255

TLD 700 in a three dimensional interpolation. The zero

point in the x=y plane marks the center of the Phantom.

As can be seen from Fig. 3 there is no increase in the

dose equivalent rate over depths. The ‘‘averaged’’ LET

and therefore the quality factor does practically not

change with increasing depth for the TLD 700 dose-meters. In contradiction the ‘‘averaged’’ LET for the

TLD 600 (data not shown here, r � �10%) increases

with depth leading to an almost constant dose equiva-

lent rate for TLD 600. The constancy of this dose

equivalent rate for the TLD 600 can therefore be ex-

plained by an increasing contribution of thermal and

epithermal neutrons with increasing depth inside the

Phantom. Therefore the HTR and consequently thedetermined ‘‘averaged’’ LET are enhanced due to these

neutron contributions in contrast to the TLD 700

measurements. The TLD 700 results, therefore, provide

a lower limit for the dose equivalent. The assessment of

the contribution of the neutron spectra to the total dose

equivalent based on the extended pair method is cur-

rently under progress and first results show an non

neglectable contribution of neutron dose for increasingdepths in the Phantom.

3.2. Project RBO-2 on ISS

The following Table 3 shows the absorbed dose rates

in water for 3 different kind of TLDs. The differences in

the dose rate far same positions are due to the different

LET efficiencies of the TLDs. The highest dose rate was

TLD 700H

ose

)

r (%) Absorbed dose

rate (lGy/d)

r (%)

2.8 275 4.8

2.0 241 7.9

3.4 234 11.9

4.8 190 5.0

7.7 185 8.6

1.0 245 7.8

1.4 238 4.5

TLD 600–TLD 700

se r (%) c – equiv. neutron dose

(lGy/d)

r (%)

1.8 9 2.3

1.2 12 4.3

1.4 8 1.7

3.3 9 3.5

1.1 12 6.5

2.5 10 2.9

3.8 11 4.2

Fig. 4. Dose equivalent rate for TLD 600 and TLD 700 dosemeters

onboard the ISS.

Table 5

Neutron dose contribution

Positions Neutron dose equivalent (lSv/d) r (%)

A11 31 8.7

A12 41 7.4

A13 27 6.2

A14 31 6.9

A15 41 8.8

A16 34 6.6

A17 37 7.3

1418 T. Berger et al. / Advances in Space Research 34 (2004) 1414–1419

observed at position A11 which was the ‘‘commander

cabin’’ – the sleeping quarter of the commander.

Table 4 gives the absorbed dose rates in water for the

TLD 600 and TLD 700 dosemeters. The higher dose rate

in the TLD 600 is due to a neutron contribution to themain dosimetric peak 5 of these TLDs. We could ob-

serve for all the 7 positions a higher dose rate for the

TLD 600 resulting in a neutron contribution to the total

dose equivalent which is not neglectable. Also shown in

Table 4 is the gamma equivalent neutron dose obtained

by subtracting the TLD 700 from the TLD 600 dose

readings.

Based on the HTR method the total dose equiva-lent rates are calculated. The data for the different

Table 6

Comparison of absorbed dose rates on ISS and on space station MIR

MIR (Phantom phase 1 and 2 exposure), absorbed dose rate (lGy/d) I

Commander cabin 359 (TLD 600) P

332 (TLD 700)

Board engineer cabin 385 (TLD 600) P

360 (TLD 700)

positions can be seen in Fig. 4. The highest dose

equivalent rate with up to 630 lSv/d is observed in

the commander cabin. Lowest dose rates are in posi-

tion A14 which is close to the board toilette. This

data was also seen in previous measurements onboard

space station MIR. Differences in the reading of theTLD 600 and the TLD 700 data are due to the

contribution of thermal and epithermal neutrons in-

side the space station.

Taking into account the gamma equivalent neutron

dose calculated by subtracting the TLD 600 from the

TLD 700 dose values and the neutron ambient dose

equivalent H*(10) calculated by means of the FLUKA

code (Mitaroff, 2002) an average calibration factor of3.39� 0.2 Sv/Gy was determined for the CERF refer-

ence field. Applying this calibration factor to the gamma

equivalent neutron dose values from the ISS shown in

Table 4 gives the neutron dose equivalent rates deter-

mined by TLDs for the ISS based on the calibration at

CERF (see Table 5).

4. MIR and ISS dose rates

To compare the dose readings from the measure-

ments on the ISS and on space station MIR we de-

cided to take the values from the commander cabin

and from the board engineer cabin on MIR and

compare them with data from the positions A11 and

A12 on the ISS. As can be seen in Table 6 the doserates for the MIR are in both positions higher more

pronounced for the board engineer cabin where the

dose rate increased more than 50%. There are some

reasons for this. First the measurement on MIR have

been performed in the timeframe from May 1997 to

February 1998 (commander cabin) and May 1998–

August 1998 (board engineer cabin) whereas the data

from ISS is taken from February to November 2001.We have 4 years difference in measurements and also

therefore different solar activities in these periods. A

second reason is the different shielding environment at

MIR and on the ISS. As can be seen from the mea-

surements on MIR and on the ISS the dose rates are

different, based on different shielding contribution and

also on the influence of the solar cycle.

SS (Project RBO – 2), absorbed dose rate (lGy/d)

osition A11 302 (TLD 600)

292 (TLD 700)

osition A12 259 (TLD 600)

248 (TLD 700)

T. Berger et al. / Advances in Space Research 34 (2004) 1414–1419 1419

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