absorbed doses in october–november 2003 onboard the russian segment of the international space...

106

ISSN 0010-9525, Cosmic Research, 2006, Vol. 44, No. 2, pp. 106–110. © Pleiades Publishing, Inc, 2006.Original Russian Text © V.M. Petrov, V.V. Bengin, V.A. Shurshakov, M.I. Panasyuk, Yu.V. Kutuzov, O.V. Morozov, A.G. Myasnikov, M.V. Tel’tso, A.V. Markov, A.N, Volkov, V.I. Lya-gushin, I.V. Nikolayev, A.P. Alexandrin, 2006, published in Kosmicheskie Issledovaniya, 2006, Vol. 44, No. 2, pp. 112–117.

INTRODUCTION

Monitoring of the radiation conditions in the Ser-vice Module of the

International Space Station

(

ISS

)during solar proton events in the end of October –beginning of November, 2003 was performed by theradiation control system (RCS) designed for determina-tion of the level of radiation impact on the

ISS

crew.Sensitive elements of the system are placed in unitsDB-8 and in dosimeter R-16. All four blocks DB-8 areidentical. Each of them consists of two totally indepen-dent channels including a silicon semiconductor detec-tor with a thickness of 300

µ

m and area of 1 cm

2

, and asubsequent circuit of signal processing. One of thedetectors is shielded by a lead layer 2.5 mm thick.

Two ionization chambers are sensitive elements ofdosimeter R-16. One of these chambers has the addi-tional shield from plexiglass with a thickness of 3 cm.

For radiation control onboard the station thearrangement of units DB-8 inside it is very essential.The points of arrangement were chosen in such a waythat one could provide for various conditions of shield-ing the RCS detectors by constructions and devices ofthe station. This was necessary in order that when ana-lyzing the results it would be possible to determine thedose absorption curve and to use it for calculating theabsorbed dose at any point of the station. The data aboutarrangement of RCS units are presented in Table 1. The

results of measurements are transmitted to the Earth viaa telemetry channel.

RESULTS OF MEASUREMENTS

The data obtained after deciphering and analysis oftelemetry information are presented below.

Dynamics of dose accumulation according to the dataof RCS detectors DB-8 is shown in Fig. 1. A similardependence derived from the data of the R-16 dosime-ter is presented in Fig. 2. As an initial level for theseplots the readings of corresponding detectors at 00:00

Absorbed Doses in October–November 2003 onboard the Russian Segment of the


according to the Data of Radiation Control System

V. M. Petrov

a

, V. V. Bengin

a

, V. A. Shurshakov

a

, M. I. Panasyuk

b

, Yu. V. Kutuzov

b

, O. V. Morozov

b

, A. G. Myasnikov

b

, M. V. Tel’tsov

b

, A. V. Markov

c

, A. N, Volkov

c

, V. I. Lyagushin

c

, I. V. Nikolayev

c

, and A. P. Alexandrin

c

a

Institute of Medical and Biological Problems, Russian Academy of Sciences, Khoroshevskoe sh. 76a, Moscow, 123007 Russia

b

Skobeltsyn Institute of Nuclear Physics, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia

c

“ENERGIYA” Space and Rocket Corporation, Korolev, Moscow oblast, Russia

Received May 24, 2004

Abstract

—The results of radiation control onboard the Service Module of the


areconsidered for the period of increased radiation background from 28 to 30 October, 2003. The values of addi-tional irradiation dose caused by strong solar proton events on October 28 and 29, 2003 are obtained. A com-parison is made with similar data obtained in the periods of disturbed radiation conditions of fall 2001. Theresults of estimating the dependence of the absorbed dose on the shield thickness, based on the onboard mea-surements, are presented. It is established that the daily-averaged dose power onboard the

International SpaceStation

increased after the solar proton events of October 2003.

PACS numbers:

92.60.Vb

DOI:

10.1134/S0010952506020031

Table 1.

The points of arrangement of RCS unit detectorson the Service Module of the

ISS

Unit name Unit arrangement

DB-8 no. 1 On the right board behind panel no. 410

DB-8 no. 2 On the left board behind panel no. 244 (cabin)

DB-8 no. 3 On the right board behind panel no. 447 (cabin)

DB-8 no. 4 On the right board behind panel no. 435

R-16 On the ceiling of the large diameter compartment behind panel no. 327

BKP On the right board behind panel no. 447 (cabin)

AI On the right board behind panel no. 447 (cabin)

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ABSORBED DOSES IN OCTOBER–NOVEMBER 2003 ONBOARD THE RUSSIAN SEGMENT 107

on October 21, 2003 were taken. Here and below, themean Greenwich time is used.

Unfortunately, a failure of channel D2 of instrumentR-16 took place on October 25. The channel becamefunctioning again only after 20:00 on October 28,therefore, the first part of enhancement has been missedin the data of this channel (horizontal part of the plot inFig. 2). The data of this channel are of considerableinterest, since ionization chamber of channel D2 has noadditional shield from plexiglass and, therefore, it ismore sensitive to changes in radiation environment.Nevertheless, the data of other detectors are availableand this made it possible to control the radiation condi-tions onboard the

ISS

reliably during the entire periodof disturbance.

Three periods of considerable increase in theonboard dose power were observed.

The first period started on October 28 at 15:25, afterthe appearance of high-energy SCR protons in the near-earth space [1]. At this time the trajectory of

ISS

flightintersected the zone of penetration of energetic chargedparticles situated above the southern part of the Indian

Ocean. To 19:00 of October 28 the

ISS

trajectory leftthe zone of SCR penetration. Therefore, the onboarddose power was reduced down to usual level andremained low until 08:15 on October 29 in spite of thefact that precisely in this period a maximum of the fluxof solar cosmic ray protons was observed according tothe data of the

GOES

satellite.

1

The second period has begun at 08:15 on October 29,when the trajectory of

ISS

flight again entered thezone of SCR penetration. This period came to an enddue to decreasing fluxes of SCR protons at 12:15 onOctober 29, after passing through a zone above thenorth of Canada.

The third period is due to a new solar flare that tookplace on October 29, at 20:40.

2

A correspondingincrease of the onboard dose power was observed muchlater: in the period from 07 to 13:00 on October 30. It isthis period that corresponds to the time of the next pas-sage of

ISS

through zones of penetration of energeticcharged particles.

The first period is characterized by a hard spectrumof SCR protons incident on the Earth’s magnetosphereand by a low level of geomagnetic disturbance.

3

The second period has the largest accumulated doseand is characterized by a softer spectrum of protons andby the moderate level of geomagnetic disturbance.

The third period had an extremely strong geomag-netic storm as a background. Therefore, in spite of thefact that proton fluxes were much lower than during thepreceding SCR enhancement, the values of absorbeddoses onboard the station turned out to be only slightlylower.

Table 2 presents the values of absorbed doses due tocontribution of SCR. (The values of background GCRand ERB doses typical for undisturbed conditions aresubtracted from detected dose increments.)

1

SEC’s Anonymous FTP Server, Lists of Solar Geophysical data,

GOES

Energetic Proton and Electron Data, http://www.sel.noaa.gov/ftpmenu/lists/particle.html.

2

Viola Raben http://www.sel.noaa.gov/ftpdir/lists/xray/20031029_G10xr_1m.txt.

3

http://sdcbd.kugi.kyoto-u.ac.jp.

5

Oct 26Oct 21 Oct 31 Nov

05 Nov 10, 2003

0

DB-8 no. 4(d)

5

0

DB-8 no. 3(c)

5

0

DB-8 no. 2(b)

5

0

DB-8 no. 1(a)

10

15Dose, mGy

Not shieldedProtected

Fig. 1.

Dynamics of dose accumulation according to thedata of DB-8 units nos. 1 (a), 2 (b), 3 (c), and 4 (d).

1

Oct 26Oct 21 Oct 31 Nov 05, 2003

0

2

3Dose, mGy

D2D1

Fig. 2.

Dynamics of dose accumulation according to thedata of dosimeter R-16. Channel D1 corresponds to data ofthe ionization chamber with additional plexiglass shield 3cm thick.

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COSMIC RESEARCH

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PETROV et al.

Table 2.

SCR doses recorded by RCS detectors in October 2003

Measuring instrumentDose for the period from

15:00 to 20:00 UT on Octo-ber 28, 2003, mGy (mrad)

Dose for the period from 08:00 to 20:00 UT on Octo-ber 29, 2003, mGy (mrad)

Dose for the period from 09:00 to 20:00 UT on Octo-ber 30, 2003, mGy (mrad)

DB-8 no. 1 not shielded 1.73 (173) 4.90 (490) 2.02 (202)

protected 1.19 (119) 2.00 (200) 1.20 (120)

DB-8 no. 2 not shielded 0.80 (80) 2.08 (208) 0.906 (90.6)

protected 0.50 (50) 0.66 (66) 0.49 (49)


protected 0.69 (69) 0.76 (76) 0.64 (64)


protected 0.30 (30) 0.294 (29.4) 0.246 (24.6)

R-16 channel D2 (not shielded) – 0.60 (60) 0.40 (40)

channel D1 (protected) 0.15 (15) 0.10–0.15 (10–15) 0.05–0.10 (5–10)

Table 3.

Absorbed doses produced by SCR protons in the periods of disturbed radiation environment in autumn 2001

Measuring instrument Dose in event on September 24,2001, mGy (mrad)

Dose in event November 4,2001, mGy (mrad)

DB-8 no. 1 not shielded 1.65 (165) 2.60 (260)

protected 0.75 (75) 1.10 (110)


protected 0.80 (80) 0.40 (40)


protected 0.41 (41) 0.39 (39)


protected 0.14 (14) <0.04 (<4)

R-16 channel D2 (not shielded) 1.25 (125) 0.60 (60)

channel D1 (protected) 0.20 (20) 0.10–0.15 (10–15)

Table 4.

Mean daily dose powers recorded by RCS detectors in October–November 2003

Measuring instrumentMean daily dose power for the period

from 00:00 UT on October 21 to 07:00 UT on October 28, 2003, mGy per day

Mean daily dose power for the period from 00:30 UT on October 31 to 22:50 UT on November 9, 2003, mGy per day

DB-8 no. 1 not shielded 0.207 0.301

protected 0.210 0.271







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ABSORBED DOSES IN OCTOBER–NOVEMBER 2003 ONBOARD THE RUSSIAN SEGMENT 109

The data presented in Table 2 illustrate a consider-able difference of doses in station compartments in theperiod of worsened radiation conditions and the effi-ciency of possible measures to reduce the levels of radi-ation impact on the crew by passing to more protectedzones of the

ISS

.We emphasize that the values of absorbed doses

onboard the

ISS

during solar proton events in October2003 turned out to be substantially less than the dosesdetected on the

Mir

station in October 1989. Compar-ing the values presented in Table 2, one can estimate thetotal dose value for channel D2 of instrument R-16.Based on the data of the protected channel of unit DB-8no. 2 (nearest in indications), this value is estimated as1.4 mGy (140 mrad). The total dose value for channelD2 of instrument R-16 detected onboard the

Mir

stationfrom solar proton events in October 1989 was equal to30.7 mGy (3070 mrad) [1]. As was shown in [2], sostrong difference in doses at close parameters of thefluxes and spectra of SCR protons could be explainedboth by different conditions of penetration to the flighttrajectories of the stations and by the higher degree ofprotection of the R-16 instrument on the

ISS

as com-pared to the

Mir

station.The absorbed doses produced by SCR protons in

October 2003 are close to the values detected in the peri-ods of disturbed radiation conditions onboard the

ISS

inautumn 2001, though slightly exceed them. Table 3 givescorresponding values taken from paper [3]. From thedata presented in Tables 2 and 3 one can also see that

10

–1

Dose, mGy

1

10

–2

10

1

November 28, 2003

MeasurementsCalculation

10

–1

1

10

–2

November 29, 200310

1

10

–1

1 10

1

10010

–2

November 30, 200310

1

Shield thickness, g/cm

2

(a)

(b)

(c)

Fig. 3.

Dependence of the dose on shield thickness in theperiods: (a) 15:00 to 20:00 UT on October 28, 2003,

R

0

=150 MV,

N

0

= 3.5

×

10

6

protons per cm

2

; (b) 08:00 to20:00 UT on October 29, 2003,

R

0

= 100 MV,

N

0

= 8.5

×

10

6

protons per cm

2

; (c) 09:00 to 20:00 UT on October 30,2003,

R

0

= 130 MV,

N

0

= 3.5

×

10

6

protons per cm

2

.

–180 –120 –60 0 60 120 180

°

–60

–30

–90

0

30

60

90

°

Dose power

,

mrad per hour

1000.0

100.0

10.0

1.0

0.1

Fig. 4.

Secondary maximum of the dose power after passing through the SAA zone.

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PETROV et al.

one of the tasks formulated when designing RCS (toprovide for various conditions of shielding the RCS bythe station instrumentation) is accomplished. The datathus obtained were used to estimate the dependence ofthe dose attenuation on the shield thickness. To thisend, effective values of the thickness of detector shield-ing were calculated for every period under consider-ation. The functions of protectability obtained in [4] fordetectors DB-8 served as initial data for these calcula-tions. The results are shown in Fig. 3 in the form ofdose dependence (in silicon) on the shield thickness.Diamonds represent the measurement data (fromTable 2). The curves in all plots are fits of the functionscalculated according to the method of [5] with the spec-trum of SCR protons presented in the exponent (inrigidity) form [6]. The spectral parameters used foreach approximation are given in the figure captions. Itis worthwhile to note that, due to influence of the geo-magnetic field and orbital motion of the station, the val-ues of characteristic rigidity

R

0

of the spectrum thatforms doses onboard the station turned out to be signif-icantly larger than those calculated from the spectra ofprotons detected by the

GOES

satellite. This is relatedto an increased contribution of energetic protonsbecause of the influence of the boundary of the regionof penetration.

No significant effect of other solar proton events inthe end of October – beginning of November, 2003 onthe radiation conditions onboard the

ISS

has beenfound. One can mention a small increase of the dailymean dose power after October 30. Table 4 presents thevalues of daily mean dose power before and after theenhancements discussed above for each detector ofDB-8 units.

All units except for DB-8 no. 2 show increasing val-ues, especially well seen for the least shielded unit DB-8no. 1. The cause of increasing mean daily dose poweris, apparently, some variation of the structure of theEarth’s radiation belt produced by geomagnetic distur-bances and SCR [7, 8, 9].

Figure 4 presents a segment of the

ISS

trajectory,and underneath the plots of the dose power recorded byunshielded and shielded detectors of the DB-8 unit no.1 are shown. The second maximum of the dose powerafter passing the South Atlantic Anomaly zone is wellseen. This illustrates the effect on radiation conditionsonboard the

ISS

made by nonstationary processesinside the ERB.

CONCLUSION

The RCS functioning onboard the Russian Segmentof the

ISS

allowed us to reliably control the radiationenvironment onboard the

ISS

during the strong solarproton events of October 2003. The contribution of

solar cosmic rays to the absorbed dose comprised fortwo days of flight (from 15:00 on October 28 to 15:00on October 30) 0.85 mGy (85 mrad) in the region ofworking table in the large-diameter compartment ofthe Service Module (panel no. 435) and 8.65 mGy(865 mrad) in the region of panel no. 410. These valuesof dose increment are the largest throughout the entireperiod of monitoring onboard the

ISS.The data obtained give initial information for verifi-

cation of the model descriptions of radiation conditionson the trajectory of ISS flight and for methods of calcu-lating the protectability conditions and dose valuesonboard the station in the periods of solar protonevents.

REFERENCES

1. Benghin, V.V., Petrov, V.M., Teltsov, M.V., et al., Dosi-metric Control onboard the MIR Space Station duringthe Solar Proton Events of September–October 1989,Nucl. Tracks Radiation Meas., 1992, vol. 20, no. 1,pp. 21–23.

2. Bondarenko, V.A., Mitrikas, V.G., and Tsetlin, V.V.,Large Proton Disturbances in the Orbit: 14 Years Later,Kosm. Issled., 2004, vol. 42, no. 6, pp. 663–667.

3. Petrov, V.M., Bengin, V.V., Shurshakov, V.A., et al.,Characteristics of Radiation Environment onboard theRussian Segment of the ISS Measured by the RadiationMonitoring System, Workshop on Radiation Monitor-ing of the ISS, Paris: France, Sep. 2–4, 2002 (http://www.magnet.oma.be/wrmiss/workshops/seventh/work-shop. html).

4. Mitrikas, V.G., A Model of Protectability for InhabitedCompartments of a Service Module of the InternationalSpace Station, Kosm. Biol. Aviakosm. Med., 2004.

5. RD 50-25645.208-86. Metodicheskie ukazaniya. Bezo-pasnost’ radiatsionnaya ekipazha kosmicheskogo appa-rata v kosmicheskom polete. Metodika rascheta poglo-shchennoi i ekvivalentnoi doz ot protonov kosmicheskikhluchei za zashchitoi (RD 50-25645.208-86: TechnicalInstructions on Radiation Safety of Spacecraft Crew in aSpace Flight. Procedures of Calculating Absorbed andEquivalent Doses from Cosmic Ray Protons behind aShield), Moscow: Gosstandart SSSR, 1986.

6. GOST (State Standard) 25645.134-86: Radiation Safetyof Spacecraft Crew during Space Flights. Solar CosmicRays: A Model of Proton Fluxes, Moscow: 1986.

7. Shurshakov, V.A., Petrov, V.M., and Makhmutov, V.S.,New Radiation Belt Dynamics according to Measure-ments Made by the Lyulin Dosimeter onboard the MIRSpace Station in 1991, Radiation Measurements, 1996,vol. 26, no. 3, pp. 379–384.

8. Dachev. Ts., Semkova, J.V., Matviichuk, Yu.N. et al.,Adv. Space Res., 1998, vol. 22, pp. 521–524.

9. Badhwar, G.D., Radiation Measurements in Low EarthOrbit: US and Russian Results, Health Physics, 2000,no. 79, pp. 507–514.

absorbed doses in october–november 2003 onboard the russian segment of the international space...

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