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Verification of shielding effect by the water-filled materialsfor space radiation in the International Space Station using

passive dosimeters

S. Kodaira a,, R.V. Tolochek b, I. Ambrozova c, H. Kawashima a, N.Yasuda a,1,M. Kurano a, H. Kitamura a, Y. Uchihori a,I. Kobayashi d,H. Hakamada d, A.Suzuki d,

I.S. Kartsev b, E.N. Yarmanova b, I.V. Nikolaev e, V.A. Shurshakov b

a Radiation Measurement Research Section, National Institute of Radiological Sciences, Chiba, Japanb State Scientific Center of Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia

c Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Prague, Czech Republicd Nagase Landauer Ltd., Ibaraki, Japan

e Rocket Space Corporation, Energia, Moscow Region, Russia

Received 3 August 2013; received in revised form 11 October 2013; accepted 15 October 2013Available online 24 October 2013

Abstract

The dose reduction effects for space radiation by installation of water shielding material (protective curtain) of a stack boardconsisting of the hygienic wipes and towels have been experimentally evaluated in the International Space Station by using passivedosimeters. The averaged water thickness of the protective curtain was 6.3 g/cm2. The passive dosimeters consisted of a combination

of thermoluminescent detectors (TLDs) and plastic nuclear track detectors (PNTDs). Totally 12 passive dosimeter packages wereinstalled in the Russian Service Module during late 2010. Half of the packages were located at the protective curtain surface and theother half were at the crew cabin wall behind or aside the protective curtain. The mean absorbed dose and dose equivalent rates aremeasured to be 327lGy/day and 821lSv/day for the unprotected packages and 224 lGy/day and 575lSv/day for the protected pack-ages, respectively. The observed dose reduction rate with protective curtain was found to be 37 7% in dose equivalent, which was con-sistent with the calculation in the spherical water phantom by PHITS. The contributions due to low and high LET particles were foundto be comparable in observed dose reduction rate. The protective curtain would be effective shielding material for not only trapped par-ticles (several 10 MeV) but also for low energy galactic cosmic rays (several 100 MeV/n). The properly utilized protective curtain willeffectively reduce the radiation dose for crew living in space station and prolong long-term mission in the future.2013 COSPAR. Published by Elsevier Ltd. All rights reserved.

Keywords: Space radiation dosimetry; Water shield; Dose reduction; Passive dosimeters; CR-39; TLD

1. Introduction

The International Space Station (ISS) crew is constantlyexposed to space radiation consisting of different kind ofcharged particles with various energies and nuclear charges(Benton and Benton, 2001). The radiation dose comesmainly from protons and helium ions which are mostlypresent in space radiation. The contribution of heavy com-ponents (Z > 2 ions) makes increase of dose equivalent due

0273-1177/$36.00 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.asr.2013.10.018

Corresponding author. Address: Radiation Measurement ResearchSection, National Institute of Radiological Sciences, 4-9-1 Anagawa,Inage, Chiba 263-8555, Japan. Tel.: +81 43 206 3479; fax: +81 43 2063514.

E-mail address:koda@nirs.go.jp(S. Kodaira).1 Present address: The Research Institute of Nuclear Engineering,

University of Fukui, Fukui, Japan.

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Advances in Space Research 53 (2014) 17

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to the high LET (linear energy transfer) with high qualityfactor related to the relative biological effectiveness (ICRP,1991). Moreover, primary high energetic charged particlesproduce not only secondary charged particles but also fastneutrons due to nuclear interaction with materials. Thebiological effects by fast neutrons are also considerable

component in terms of the space radiation dose equivalent(Lewis et al., 2012). The typical daily dose in the ISS isranging from about 0.5 to 1 mSv depending on the solaractivity and the altitude and attitude of the ISS(Lishnevskii et al., 2010; Ambrozova et al., 2011; Finoet al., 2011; Kodaira et al., 2013). The effective dose limitsof 10 yr career for astronauts are recommended to be400 mSv (female) and 700 mSv (male) for 25 yrs old(NCRP No. 142, 2002). The radiation risk of astronautsin the ISS is controlled under such recommended limita-tions with actual dose measurement.

The astronauts will be exposed to high dose of spaceradiation for up-coming long-term missions on the Mars

and Moon. Especially, the cruising time in the interplane-tary space is estimated to be 260 days (fast transit missioncase) or 500 days (typical mission case) for a manned mis-sion to the Mars (Hoffman and Kaplan, 1997). In additionto dose exposure during the transit, they will work on theMars for 30 days (typical short mission case) or 458 days(typical long mission case). The radiation dose of interplan-etary space cruising is recently reported to be 660 mSv foreven shortest round-trip case to the Mars (Zeitlin et al.,2013). In the protection strategy using shielding materials(Wilson et al., 1997), an interplanetary spacecraft wouldrequire substantial shielding of 50 g/cm2 of aluminum, if

500 mSv annual dose limit for astronaut exposure is notto be exceeded (Wilson et al., 2001).

The shielding effects have been verified for various mate-rials such as aluminum and polyethylene on the ground-based beam experiments (e.g.,Miller et al., 2003; La Tessaet al., 2005; Dewitt et al., 2009). In general, the hydroge-nous materials would be most effective shields for spaceradiation due to the mass at both stopping and fragment-ing of particles. However, at the current status, the radia-tion protection still depends on the material with thethickness of a few g/cm2 of vehicle walls and the internalequipments of the ISS module. As an another protectionmethod, the active shielding with electrostatic and magne-tostatic fields deflecting ionized particles from a region sur-rounding the spacecraft has been verified long years ago(Sussingham et al., 1999). However, there are still severalissues to be addressed, which are about the realistic config-uration such as coils, power sources, refrigeration, and sup-port structure and the advantage compared with thepassive method from the viewpoint of total mass to beinstalled in spacecraft (Townsend, 2005).

In this paper, we present the dose reduction effects forspace radiation by the additional water shielding material(protective curtain) of stack board consisting of thehygienic wipes and towels which have been already deliv-

ered to ISS. These materials will be delivered in the future

missions to interplanetary. In this meaning, it is consideredthat the protective curtain is as one of ideal shieldingmaterials.

2. Protective curtain and dosimeters

2.1. Protective curtain

The material of the protective curtain consists of thehygienic wipes and towels which have been alreadyinstalled in the Russian Service Module as shown inFig. 1. The hygienic tools were stored into the protectivecurtain at 4 layers, which is corresponding to the additionalwater shielding thickness of 6.3 g/cm2. The total mass ofthe protective curtain is 67 kg, it was installed along theouter wall of the starboard crew cabin in the Russian Ser-vice Module.

2.2. Passive dosimeter packages

A combination of thermoluminescence detectors (TLD)and plastic nuclear track detectors (PNTD) was employedas the dose evaluation method of space radiation, whichcovers whole LET range relevant to radiation protectionin spaceflight. TLDs measure absorbed dose from photonsand charged particles with high efficiency for LET

1H2O

10 keV/lm. The data from the two types of

detectors were combined to yield values of total absorbeddose and total dose equivalent accumulated over the dura-

tion of the exposure (Doke et al., 1995; Benton et al., 2002;Hajek et al., 2008; Tawara et al., 2011).

Four types of TLDs provided from three participatinginstitutes, as summarized in Table 1, and one of PNTD(CR-39 HARZLAS TD-1 manufactured by Fukuvi Chem-ical Industry, Japan) were employed. The size of PNTDwas 26 mm 26 mm 0.9 mm. A dosimeter package con-sists of three layers which are two PNTD plates and oneTLD holder. For the purpose of intercomparison of dosemeasurement by several types of TLD in space, eachTLD has been independently analyzed in each institute fol-lowing its own protocol. The PNTD has been analyzed inNIRS and NPI with a high speed imaging microscope sys-tem (Yasuda et al., 2005) after the chemical etching for 8 hin 7 N NaOH solution at 70 C. The mean value of amountof bulk etch was 14.6 0.7 lm. All detectors have beencalibrated by means of heavy ion beams from HIMAC(Heavy Ion Medical Accelerator in Chiba) at NIRS (NIRSreport, 2009).

3. Experiment

The 12 dosimeter packages (#001#012) were installedin the Russian Service Module of the ISS from June 16,2010 to November 26, 2010. The exposure duration was

163 days. Half of the packages were located at the

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protective curtain surface and the other half were at thecrew cabin wall behind or aside the protective curtain asshown in Fig. 2. The dose reduction effect by protectivecurtain was experimentally verified by the dose variationamong 6 pairs (AF) as summarized in Table 2. The thick-ness of protective curtain was 6.3 g/cm2 in water for pro-tected packages. It should be noted that there was a thickglass window of 5 g/cm2 at forward side (toward space)of unprotected packages of #007#008. In other words,both #007#008 have been actually shielded by the othermaterial (glass window) which is thicker than wall materi-als (aluminum of 1.5 g/cm2).

4. Results

The differential LET spectra for 6 pairs (AF) measuredby PNTDs are shown inFig. 3. The LET spectra for pro-tected (open circle) and unprotected (closed circle) pack-ages are compared in each pair. The flux is found to bedegraded in the protected packages compared with theunprotected ones. The values of absorbed dose and doseequivalent measured by TLDs and PNTDs for each pack-age are summarized inTable 3. The intercomparison resultamong each TLD type shows good agreement in absorbeddose within 4%. Similar tendency in dose variation isobserved depending on the location of package. The totaldose, covering the whole LET range of space radiation, isobtained by combining data from TLDs (10 keV/lm. The

dose equivalent was obtained by applying the LET-depen-dent definition of the quality factor defined in ICRP-60(ICRP, 1991). Since the dose results in 4 types TLDs showa consistency, hereafter NIRS-LiF;Ti,Mg TLD wasemployed as a representative for obtaining total doseresults. The total absorbed dose and dose equivalent rates,together with quality factors, are summarized in Table 4.The obvious tendency that the dose rate measured at theprotected packages is degraded compared with the unpro-tected ones is observed as a function of package location(#001#012) inFig. 4. The mean absorbed dose and doseequivalent rates are measured to be 327lGy/day and821lSv/day for the unprotected packages and 224 lGy/day and 575lSv/day for the protected packages, respec-tively. The uncertainties are from the dose variationdepending on the location inside the ISS (Ambrozovaet al., 2011).

5. Discussion

5.1. Dose reduction effects

The protective curtain effectively reduces the radiationdose as shown in Table 5(a), which summarizes the dosereduction rate obtained from the protected/unprotectedpair (AF). The dose reduction rate in dose equivalent isfound to be 37 7% except for pairs C and D. In case ofpairs C and D, the shielding effect by protective curtain isrelatively small (only about 3%). It is because the thick

glass window installed by the packages #007 and #008

Fig. 1. Protective curtain, (a) the hygienic wipes and towels, (b) the stack board, and (c) schematic drawing of stack board and its installation in the ISS.

Table 1

List of thermoluminescence detectors (TLDs) prepared by 3 institutes.Material Size Institution

LiF:Mg, Ti (tablet) 3 mm 3 mm 0.9 mmt NIRS, JapanLiF:Mg, Ti (mono crystal) 4.5 mm/ 1 mmt IBMP, RussiaCaSO4:Dy 5 mm/ 1 mmt NPI, Czech Rep.Al2O3:C 5 mm/ 1 mmt

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shielded them. The Monte-Carlo simulation on the dosereduction effect for space radiation has been reported pre-viously (Sato et al., 2011). It shows a simple simulation ofdose variation as a function of thickness in a sphericalwater phantom by means of PHITS code (Niita et al.,2006). By their simulation, the dose reduction rate in doseequivalent is estimated to be 34%, which is consistentwith the measured result of 37 7%.

The obtained dose can be categorized into four shieldingthicknesses as: (1) unprotected with a curtain but isshielded by the wall aluminum (1.5 g/cm2) for #002,#004, #010, and #012, (2) protected with the curtain(6.3 g/cm2) and the wall aluminum for #001, #003, #009,and #011, (3) shielded with the glass window (5.0 g/cm2)

for #007 and #008, and (4) shielded with the glass window

and the protective curtain for #005 and #006. Therefore,the material thicknesses for the cases (1)(4) are calculatedto be 1.5 g/cm2, 7.8 g/cm2, 5.0 g/cm2, and 11.3 g/cm2,respectively. The dose variations as a function of materialthickness are shown inFig. 5. The dose rate decreases withrepeat to depth direction exponentially. The dose reductioneffects are seemed to be small at the thickness larger than10 g/cm2 or so. It suggests that the effective dose reductionwould be expected with the protective curtain of 10 g/cm2. This experiment evaluates only the dose reductioneffect with a protective curtain for one direction in the iso-tropic space radiation fields. The dose contribution fromthe opposite direction is not reduced in this experimental

configuration. If the protective curtain covers 4pwhole sur-face inside the space vehicle, more effective dose reductionwould be expected.

We will investigate the more specific simulation withPHITS based on the actual experimental configurationand the comparison of absolute dose values with measureddata in a future paper.

5.2. Reduction effect for various LET components

For verifying the main contribution for the dose reduc-tion effect, the dose reduction rates between low LET

(

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are compared as shown in Table 5(b). The mean dosereduction due to the low and high LET components are37 2% and 37 11% in dose equivalent except for pairsC and D, respectively. The contributions of low and highLET components are found to be comparable in observeddose reduction rate. According to the simple range-energycalculations with SRIM code (Ziegler et al., 2003), the rep-resentative cosmic rays such as

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In the present measuring method, it is difficult to evalu-ate clearly the neutron dose contribution and its reductioneffect with the protective curtain. However, since the CR-39 plastic is a tissue equivalent detector, neutrons would

interact and deposit their dose to the detector in the samemanner as they would make in tissue. In fact, the neutroncomponents are measured as recoiled proton tracks in theLET spectrum. We should mention that there is a limita-tion of detectable proton energy less than about 20 MeVin CR-39 due to its registration threshold (Ogura et al.,2001). In this meaning, thus obtaining dose reductioneffects include partially neutron dose reduction by the

water shielding.

6. Conclusions

We have demonstrated the use of passive dosimeterpackages to verify the dose reduction effect for space radi-ation by installation of protective curtain. The 6 packageswere located on the protective curtain surface and the other6 packages were located on the crew cabin wall behind oraside the protective curtain. The mean absorbed dose anddose equivalent rates are 327lGy/day and 821 lSv/dayfor the unprotected packages and 224lGy/day and

575lSv/day for the protected packages, respectively. Themean dose reduction rate obtained from the dose changeamong protected and unprotected package pair was37 7% in dose equivalent, which was consistent withthe calculated results in the spherical water phantom byPHITS. The protective curtain with the thickness of6.3 g/cm2 would degrade the particle flux for not onlytrapped particles with several 10 MeV but also low energygalactic cosmic rays with several 100 MeV/n. The shieldingof the whole surface with the protective curtains inside thespacecraft would effectively reduce the space radiation dosefor crew living in space station and prolong long-term mis-sion in the future.

Fig. 4. Variations of (a) total absorbed dose (DTotal) and (b) total doseequivalent (HTotal) rates as a function of the location of dosimeterpackages. The hatched packages are protected with the curtain.

Table 5(a)The dose reduction rates in total absorbed dose (DD) and total doseequivalent (DH) obtained from the protected/unprotected pair (AF).

Pair DD [%] DH [%]

A 37.5 2.9 33.1 4.1B 41.0 1.3 44.2 2.9

C 13.6 3.9 2.8 6.5D 12.4 5.0 2.6 7.2E 34.0 2.5 27.2 4.5F 37.3 3.8 44.1 3.5

Fig. 5. Variations of (a) total absorbed dose (DTotal) and (b) total doseequivalent (HTotal) rates as a function of the material thickness.

Table 5(b)The dose reduction rates between low LET (

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Acknowledgements

We gratefully acknowledge the IBMP staff and the ISScrew for preparing, launching and recovering our detectorsduring the long duration of this experiment. This work wasperformed as a part of accelerator experiments of the Re-

search Project at NIRS-HIMAC. We would like to expressour thanks to the staff of NIRS-HIMAC for their kind sup-port throughout the experiments for detector calibrations.This international joint work was partially supported bythe Space Radiation Research Unit of the NIRS Interna-tional Open Laboratory.

References

Ambrozova, I., Brabcova, K., Spurny, F., Shurshakov, V.A., Kartsev,I.S., Tolochek, R.V., 2011. Monitoring on board spacecraft by meansof passive detectors. Radiat. Protect. Dosim. 144, 605610.

Benton, E.R., Benton, E.V., 2001. Space radiation dosimetry in low-earthorbit and beyond. Nucl. Inst. Meth. B184, 255294.

Benton, E.R., Benton, E.V., Frank, A.L., 2002. Passive dosimetry aboardthe Mir Orbital Station: internal measurements. Radiat. Meas. 35,439455.

DeWitt, J.M., Benton, E.R., Uchihori, Y., Yasuda, N., Benton, E.V.,Frank, A.L., 2009. Assessment of radiation shielding materials forprotection of space crews using CR-39 plastic nuclear track detector.Radiat. Meas. 44, 905908.

Doke, T., Hayashi, T., Nagaoka, S., Ogura, K., Takeuchi, R., 1995.Estimation of dose equivalent in STS-47 by a combination of TLDsand CR-39. Radiat. Meas. 24, 7582.

Fino, L.Di., Casolino, M., De Santis, C., Larosa, M., La Tessa, C. ,Narici, L., Picozza, P., Zacontea, V., 2011. Heavy-ion anisotropymeasured by ALTEA in the International Space Station. Radiat.Res. 176, 397406.

Hajek, M., Berger, T., Vana, N., Fugger, M., Palfalvi, J.K., Szabo, J.,Eordogh, I., Akatov, Y.A., Arkhangelsky, V.V., Shurshakov, V.A.,2008. Convolution of TLD and SSNTD measurements during theBRADOS-1 experiment onboard ISS (2001). Radiat. Meas. 43, 12311236.

Hoffman, S.J., Kaplan, D.I., 1997. Human Exploration of Mars: TheReference Mission of the NASA Mars Exploration Study Team.NASA Johnson Space Center, Houston, TX. NASA Special Publica-tion 6107.

ICRP, 1991. International Commission on Radiological Protection, The1990 Recommendations of the ICRP, ICRP Publication 60, Annals ofthe ICRP, 21, Pergamon Press, New York.

Kodaira, S., Kawashima, H., Kitamura, H., Kurano, M., Uchihori, Y.,Yasuda, N., Ogura, K., Kobayashi, I., Suzuki, A., Koguchi, Y.,Akatov, Y.A., Shurshakov, V.A., Tolochek, R.V., Krasheninnikova,

T.K., Ukraintsev, A.D., Gureeva, E.A., Kuznetsov, V.N., Benton,E.R., 2013. Analysis of radiation dose variations measured by passivedosimeters onboard the International Space Station during the solarquiet period (20072008). Radiat. Meas. 49, 95102.

La Tessa, C., Guetersloh, S., Heilbronn, L., Miller, J., Sihver, L., Zeitlin,C., 2005. Fragmentation of 1 GeV/nucleon iron ions in thick targetsrelevant for space exploration. Adv. Space Res. 35, 223229.

Lewis, B.J., Smith, M., Ing, H., Andrews, H.R., Machrafi, R., Tomi, L.,Matthews, T.J., Veloce, L., Shurshakov, V., Tchernykh, I., Khosho-oniy, N., 2012. Review of bubble detector response characteristics andresults from space. Radiat. Prot. Dosim. 150 (1), 121. http://dx.doi.org/10.1093/rpd/ncr358.

Lishnevskii, A.E., Panasyuk, M.I., Benghin, V.V., Petrov, V.M., Volkov,A.N., Nechayev, O.Yu., 2010. Variations of radiation environmentonboard the ISS in the year 2008. Cosmic Res. 48, 206210 .

Miller, J., Zeitlin, C., Cucinotta, F.A., Heilbronn, L., Stephens, D.,Wilsond, J.W., 2003. Benchmark studies of the effectiveness ofstructural and internal materials as radiation shielding for theInternational Space Station. Radiat. Res. 159, 381390.

NCRP No.142, 2002. National Council on Radiation Protection, No. 142,Bethesda.

Niita, K., Sato, T., Iwase, H., Nose, H., Nakashima, H., Sihver, L., 2006.Particle and heavy ion transport code system: PHITS. Radiat. Meas.41, 10801090.

NIRS report (NIRS-R-62), 2009. Scientific Reports of Space Experiments(IBMP-NIRS-1 to 4) in the IBMP-NIRS Collaboration, NationalInstitute of Radiological Sciences, Aug. 2009.

Ogura, K., Asano, M., Yasuda, N., Yoshida, M., 2001. Properties ofTNF-1 track etch detector. Nucl. Instr. Meth. B185, 222227.

Sato, T., Niita, K., Shurshakov, V.A., Yarmanova, E.N., Nikolauev, I.V.,Iwase, H., Sihver, L., Mankusi, D., Endo, A., Matsuda, N., Iwamoto,Y., Nakashima, H., Sakamoto, Y., Yasuda, H., Takada, M., Nakam-ura, T., 2011. Evaluation of dose rate reduction in a spacecraftcompartment due to additional water shield. Cosmic Res. 49, 319324.

Sussingham, J.C., Watkins, S.A., Cocks, F.H., 1999. Forty Years ofdevelopment of active systems for radiation protection of spacecraft. J.Astronautical Sci. 47, 165175.

Tawara, H., Masukawa, M., Nagamatsu, A., Kitajo, K., Kumagai, H.,Yasuda, N., 2011. Characteristics of Mg2SiO4:Tb (TLD-MSO-S)relevant for space radiation dosimetry. Radiat. Meas. 46, 709716.

Townsend, L.W., 2005. Critical analysis of active shielding methods forspace radiation protection. In: Aerospace Conference. IEEE, pp. 724730.

Wilson, J.W., Miller, J., Konradi, A., Cucinotta, F.A., 1997. ShieldingStrategies for Human Space Exploration. NASA Langley ResearchCenter Hampton, VA. NASA Conference, Publication 3360.

Wilson, J.W., Cucinotta, F.A., Kim, M.H., Schimmerling, W., 2001.Optimized shielding for space radiation protection. In: Phys. Med.XVII (Suppl. 1).

Yasuda, N., Namiki, K., Honma, Y., Umeshima, Y., Marumo, Y., Ishii,H., Benton, E.R., 2005. Development of a high speed imagingmicroscope and new software for nuclear track detector analysis.Radiat. Meas. 40, 311315.

Zeitlin, C., Hassler, D.M., Cucinotta, F.A., Ehresmann, B., Wimmer-Schweingruber, R.F., Briza, D.E., Kang, S., Weigle, G., Boehm, E.,Burmeister, S., Guo, J., Koehler, J., Martin, C., Posner, A., Rafkin, S.,

Reitz, G., 2013. Measurements of energetic particle radiation in transitto mars on the mars science laboratory. Science 340, 10801084.Ziegler, J.P., Biersack, J., 2003. SRIM-2003 Stopping and Range of Ions

in Matter. (http://www.SRIM.org).

S. Kodaira et al./ Advances in Space Research 53 (2014) 17 7

http://refhub.elsevier.com/S0273-1177(13)00652-2/h0005http://refhub.elsevier.com/S0273-1177(13)00652-2/h0005http://refhub.elsevier.com/S0273-1177(13)00652-2/h0005http://refhub.elsevier.com/S0273-1177(13)00652-2/h0005http://refhub.elsevier.com/S0273-1177(13)00652-2/h0005http://refhub.elsevier.com/S0273-1177(13)00652-2/h0005http://refhub.elsevier.com/S0273-1177(13)00652-2/h0005http://refhub.elsevier.com/S0273-1177(13)00652-2/h0010http://refhub.elsevier.com/S0273-1177(13)00652-2/h0010http://refhub.elsevier.com/S0273-1177(13)00652-2/h0015http://refhub.elsevier.com/S0273-1177(13)00652-2/h0015http://refhub.elsevier.com/S0273-1177(13)00652-2/h0015http://refhub.elsevier.com/S0273-1177(13)00652-2/h0020http://refhub.elsevier.com/S0273-1177(13)00652-2/h0020http://refhub.elsevier.com/S0273-1177(13)00652-2/h0020http://refhub.elsevier.com/S0273-1177(13)00652-2/h0020http://refhub.elsevier.com/S0273-1177(13)00652-2/h0025http://refhub.elsevier.com/S0273-1177(13)00652-2/h0025http://refhub.elsevier.com/S0273-1177(13)00652-2/h0025http://refhub.elsevier.com/S0273-1177(13)00652-2/h0030http://refhub.elsevier.com/S0273-1177(13)00652-2/h0030http://refhub.elsevier.com/S0273-1177(13)00652-2/h0030http://refhub.elsevier.com/S0273-1177(13)00652-2/h0030http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0035http://refhub.elsevier.com/S0273-1177(13)00652-2/h0045http://refhub.elsevier.com/S0273-1177(13)00652-2/h0045http://refhub.elsevier.com/S0273-1177(13)00652-2/h0045http://refhub.elsevier.com/S0273-1177(13)00652-2/h0045http://refhub.elsevier.com/S0273-1177(13)00652-2/h0045http://refhub.elsevier.com/S0273-1177(13)00652-2/h0045http://refhub.elsevier.com/S0273-1177(13)00652-2/h0045http://refhub.elsevier.com/S0273-1177(13)00652-2/h0050http://refhub.elsevier.com/S0273-1177(13)00652-2/h0050http://refhub.elsevier.com/S0273-1177(13)00652-2/h0050http://dx.doi.org/10.1093/rpd/ncr358http://dx.doi.org/10.1093/rpd/ncr358http://refhub.elsevier.com/S0273-1177(13)00652-2/h0055http://refhub.elsevier.com/S0273-1177(13)00652-2/h0055http://refhub.elsevier.com/S0273-1177(13)00652-2/h0055http://refhub.elsevier.com/S0273-1177(13)00652-2/h0060http://refhub.elsevier.com/S0273-1177(13)00652-2/h0060http://refhub.elsevier.com/S0273-1177(13)00652-2/h0060http://refhub.elsevier.com/S0273-1177(13)00652-2/h0060http://refhub.elsevier.com/S0273-1177(13)00652-2/h0065http://refhub.elsevier.com/S0273-1177(13)00652-2/h0065http://refhub.elsevier.com/S0273-1177(13)00652-2/h0065http://refhub.elsevier.com/S0273-1177(13)00652-2/h0075http://refhub.elsevier.com/S0273-1177(13)00652-2/h0075http://refhub.elsevier.com/S0273-1177(13)00652-2/h0080http://refhub.elsevier.com/S0273-1177(13)00652-2/h0080http://refhub.elsevier.com/S0273-1177(13)00652-2/h0080http://refhub.elsevier.com/S0273-1177(13)00652-2/h0080http://refhub.elsevier.com/S0273-1177(13)00652-2/h0080http://refhub.elsevier.com/S0273-1177(13)00652-2/h0085http://refhub.elsevier.com/S0273-1177(13)00652-2/h0085http://refhub.elsevier.com/S0273-1177(13)00652-2/h0085http://refhub.elsevier.com/S0273-1177(13)00652-2/h0090http://refhub.elsevier.com/S0273-1177(13)00652-2/h0090http://refhub.elsevier.com/S0273-1177(13)00652-2/h0090http://refhub.elsevier.com/S0273-1177(13)00652-2/h0090http://refhub.elsevier.com/S0273-1177(13)00652-2/h0090http://refhub.elsevier.com/S0273-1177(13)00652-2/h0090http://refhub.elsevier.com/S0273-1177(13)00652-2/h0090http://refhub.elsevier.com/S0273-1177(13)00652-2/h0110http://refhub.elsevier.com/S0273-1177(13)00652-2/h0110http://refhub.elsevier.com/S0273-1177(13)00652-2/h0110http://refhub.elsevier.com/S0273-1177(13)00652-2/h0115http://refhub.elsevier.com/S0273-1177(13)00652-2/h0115http://refhub.elsevier.com/S0273-1177(13)00652-2/h0115http://refhub.elsevier.com/S0273-1177(13)00652-2/h0095http://refhub.elsevier.com/S0273-1177(13)00652-2/h0095http://refhub.elsevier.com/S0273-1177(13)00652-2/h0095http://refhub.elsevier.com/S0273-1177(13)00652-2/h0095http://refhub.elsevier.com/S0273-1177(13)00652-2/h0120http://refhub.elsevier.com/S0273-1177(13)00652-2/h0120http://refhub.elsevier.com/S0273-1177(13)00652-2/h0120http://refhub.elsevier.com/S0273-1177(13)00652-2/h0120http://refhub.elsevier.com/S0273-1177(13)00652-2/h0120http://www.srim.org/http://www.srim.org/http://refhub.elsevier.com/S0273-1177(13)00652-2/h0120http://refhub.elsevier.com/S0273-1177(13)00652-2/h0120http://refhub.elsevier.com/S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