Dosimetry during the first IBIS facility flight

Adv. Space Res. Vol. 22. No. 4, pp. 517-520, 1998 01998 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-1177/98$19.00+0.00 PII: SO273-1177(98)01072-7

Pergamon

DOSIMETRY DURING THE FIRST IBIS FACILITY FLIGHT J. F. Bottollier-Depois*, F. Spumy**, L. Plawinski*, I. Votockova**, J. Bednar**, M. Visa*** and A. Labarthe*** *Institutefor Protection and Nuclear Safety, Human Health Protection and Dosimetrl, Division, Dosimetry Service, IPSN, B. P. n”6,92265 Fontenay aux Roses Cedex, France **Nuclear Physics Institute, Academy of Sciences of Czech Republic, Na Truhlarce 39/64, CZ 180 86 Prague, Czech Republic ***French National Space Agency, CNES, 2 place Maurice Quentin, Paris 1, France

ABSTRACT The dosimetry of cosmic rays was performed during the first experimental flight of the IBIS facility. Different thermoluminescent detectors (TLD) have been used to measure the contribution of the low linear energy transfer component (LET < 10 keV/pm) and plastic nuclear track detectors (PNTD) for the high linear energy tranfer (LET) component. Several parameters of tracks have been measured to determine the LET spectra of primary and secondary charged particles. The total absorbed dose rate (TLD+PNTD) during the flight was 0.23 mGy/day and the dose equivalent rate using the ICRP 60 was 0.52 mSv/day. The corresponding mean quality factor was 2.4. These results are in agreement with those obtained aboard the MIR station with a tissue equivalent proportional counter. 01998 COSPAR. Published by Elsevier Science Ltd. ENVIRONMENT IBIS is a facility developed by the French National Space Agency (CNES) and dedicated to cell biology experiments in space (Rafftn et al., 1990). IBIS houses 256 independent cassettes for culture media. The first experimental flight was performed on February 1995 aboard a Russian space capsule “ Photon ” during 15 days. The orbital inclination was 62’8, the apogee 389 km and the perigee 227 km. DETECTOR USED FOR THE IBIS EXPERIMENT Passive dosemeters have been chosen due to their easy implementation because space inside a cassette is very limited. Moreover, these techniques are often used in a space environment. In our case, two kinds of detectors have been selected to cover the whole LET range : - a set of thermoluminescent detectors (TLD) for the low LET particles (< 10 keV/pm) : protons, gamma rays, electrons. The different types of TLDs and the number for each cassette are shown on Table 1. - a stack of plastic nuclear track detectors composed of 4 layers (30x30~05 mm3 in size) for the high LET part (10 keV/pm until 1000 keV/pm). The material is polyallyldiglycoIcarbonate manufactured by Pershore (UK). 517

518

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Seven cassettes have been filled with a complete set of detectors. Three were used to evaluate the background before, during and after the flight : one in the laboratory, one for the round trip Paris Plessetsk where the rocket was launched and another one for the round trip Paris - Samara where the landing was located. Three of the four cassettes included in IBIS have been evaluated, the fourth was lost after the landing and found one month later but could not be read out, unfo~unately. T~~~L~~SCENT

DETECTOR DATA

The sensitivity of the TLDs used to gamma rays and to protons of energies higher than 50 MeV is, in terms of tissue doses, about the same (Spurny, 1993), the ratio TLDltissue of energy transfer coefficients for gamma rays and stopping powers for protons as well (Ianni et al., 1982). Consequently, TLD signals are expressed in the terms of the dose quantities in the tissue using the calibration with ?Zo gamma rays. Taking into account the irradiation geometry we are measuring the dose quantities in small tissue volume behind few mm of tissue-like materials. The ope~tion~ quantity used in radiation protection is the ambient dose equiv~ent, H*(IO) (HXP 60) Our irradiation geometry doesn’t correspond to the definition of this quantity. Nevertheless, we believe that, taking into account low LET radiation on board (high energy protons, electrons, mesons, photons), our dose equivalent values are not very different of ambient dose equivalent values. Table 1 presents results for the on board cassettes. First, one can see there that the reproducibility of readings is better for powder than for pellets. This is underst~dable in view of limited number of pellets (see table 1) and at least 10 readings of homogeneous powder. Furthermore, rather low dispersion of all data shows the good homogeneity of the field on board. The average signal of 6LiF is a little higher (on the limit of reliability} than for ‘LiF. It could be due to the presence of neutrons therm~ised on board . If it is the case, the difference of 6LiF and ‘LiF signals allows to estimate their Buence. Considering the sensitivity of 6LiF : 5x1 O“* Sv/n~crn~ (Spumy, 1984) and the difference to the ‘LiF detectors of 0.3 mSv, the thermal neutron fluence can be estimate to about 4~10~n&cm’/day (*40%). The mean value of low LET contribution to the total dose equivalent has been calculated as an average of all TLD readings. It is equal to (3.0*0.3) mSv for the mission (15 days). Table I. Dose equivafent (mSv) obtained with the~olumin~s~e~t detectors during the Bight detectors

cassette 1

cassette 2

cassette 3

I. Al203-C (5 pellets) 2. ‘LiF (powder) 3, 7LiF (powder) 4. CaS04-Dy (powder) 5. Glass Al-P (3 pellets) 6. 6LiF (3 pellets) 7. ‘LiF (3 pellets) 8. CaSO&y (3 pellets)

2.46 *to.05 3.22 *O.10 (6.15) not used 3.17 zto.07 3.02 =tO.20 3.18 50.14 2.91 *0.17 3.26 *0.24

2.64 *IO.I4 3.19fO.10 2.76 kO.03 3.02 +0.06 2.89 1tO.18 3.16*0.18

2.68 *o. 12 3.25 ztO.08 2.87 *to.04 3.10 lto.09 3.31 rto.25 3.94 Lto.40 3.39 LtO.15 3.68 10.22

3.18 10.18 3.12 *0.20

PLASTIC NUCLEAR TRACK DETECTOR DATA Charged particles impinging or created in a bulk of material mod@ the properties of a polymer along their trajectory which results in an increased chemical etch rate (VT)in comparison to the chemical etch rate of

Dosimetry During the First IBIS Facility Flight

519

und~aged bulk material (vg). As a result of etching conically developed structures occur, referred to as tracks. The etch rate vr increases with the LET of particles; a calibration gives a relationship between the vr/va ratio and the LET (Spurny et al., 1996). The detection threshold at our chemical etching conditions (5N NaOH, 70°C) and the minimum track dimension taken into account is 15 keV/um (v&j = 1.12). PNTDs were evaluated using an automatic optical analysing system, LUCIA II, based on Leitz optical microscope and specially developed software (Spurny et al.,1996). Several track parameters are measured; a procedure to optimise the value of vT/ve ratio is adopted. To pass from VT/Q ratios to the LET spectrum, a calibration with charged particles had been realised. Figure 1 shows the number of tracks per cm’ in dependence of LET for the background and a stack which has flown. The total track density (> 15 keV/pm) is 4.3~10~ cmm2for the on board sample and I .7x103 crnm2 for the ground sample. It should be stressed that our method gives the LET spectra for all primary and secondary charged particles. Imperfections in the detector surface simulate structures similar to real tracks, particularly that of protons. These imperfections represent the dominant part of the background. Furthermore, it should be mentioned that the tracks of primary charged particles represent only a very minor part of the total number of tracks (few %), most of the tracks are formed by secondary charged particles created in the neighbouring and in the bulk of PNTD material through nuclear interactions of high energy charged particles and neutrons. The absorbed dose D expressed in gray (1 Gy = 1 J/kg) and the dose equivalent H are given by the following relationships : D = C N(L) L dL and H = C N(L) L q(L) dL where N(L) is the track number in the LET interval L and L+dL, q(L) is the quality factor function as defined by the International Commission on Radiological Protection (Publications ICRP 21 and 60). Results obtained with the polyallyldiglycolcarbonate during the mission for particles with a LET greater than 15 keVlum are : D = 0.4 mGy, Hrc~p~i= 3.9 mSv and Hi~ai~= 4.8 mSv. The difference observed on the dose equivalent is due to events with a LET between 20 and 200 keV/um for which the q(L) function is higher in ICRP 60 than in ICRP 2 1. It should be noted that these values represent the dose quantities in small tissue volume covered by few mm of tissue-like material. 1oooo,o

1000,0

100,o

10,o

1s 0.1

LET (keV/um)

Fig. I. Number of particle tracks in polyallyldiglycolc~bonate for ground and flight samples.

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CONCLUSION Results of our measurements give an estimate of radiation characteristics on board a satellite. Thermoluminescent detectors characterise mostly the contribution of particles with LET lower than 10 keV/um, plastic nuclear track detectors the contribution of particles between 15 and 700 keV/um. The total values are obtained as the sum of both components. Consequently, the total dose quantities in small tissue element covered by few mm of tissue-like material are : the absorbed dose rate, D = 0.23 mGy/day, the dose equivalent rate, HICRPZ~ = 0.45 mSv/day and Hr~nr~ = 0.52 mSv/day and the corresponding mean quality factor (IUD), Q ICR~~I = 2.0 and Q 1~60 = 2.3. These results are consistent with those obtained aboard the MIR station with the NAUSICAA TEPC counter, if the difference of altitude is considered (300 kms for IBIS and 400 kms for MIR). This instrument measures the dose quantities in small tissue volume covered with 10 mm of tissue-equivalent material. The values determined (Bottollier-Depois et al., 1993) were : D = 0.45 mGy/day, Hrc~2r = 0.9 mSv/day and Q rc~~i = 2. Our values for the low LET component can be also compared with the data obtained aboard biosatellites Cosmos, flying roughly at the same altitude and inclination. The dose rates varied between 0.18 and 0.3 mGy per day depending on the sun activity (Benton et al., 1990).

REFERENCES Benton, E.V., L.P. Chambers, J.P. Connolly, E.E. Kovalev, V.E. Dudkin and A.M. Marenny, Radiation and radiobiological investigations on biosatellite Cosmos 1887, Nuclear Tracks Radiation Measurements, 17, N” 2 (1990). Bottollier-Depois, J.F., V.D. Nguyen, L. Lebaron-Jacobs, M. Siegrist, C. Andre-Deshays, 0. Marsal, V.M. Petrov, S.B. Koslova, M. Tognini, and S. Avdeev, Dose rate and LET spectrum aboard MIR station since Antares until Altair mission, Proceedings of the fifth European Symposium on Life Sciences Research in Space, Arcachon, France (1993). Ianni, J. et al, Proton range-energy tables, Atomic Data Nuclear Tables, 27, N” 2 - 5 (1982). International Commission on Radiological Protection, publication 21, (1973). International Commission on Radiological Protection, publication 60, (199 1). Raffin, J., H. Bozouklian, L. Braak and G. Gargir, A new facility for gravitational biology, 41th Congress of the International Astronautical Federation, Dresden, GDR (1990). Spurny, F., Methodes dosimetriques pour l’irradiation externe et leur utilisation, ThBse de Docteur ds Sciences, Prague (1984). Spurny, F., Comparative dosimetry measurements in radiotherapy proton beams of LNP JINR with TLDs, Report IRLJ CAS 36.5193, Prague (1993). Spurny, F., J. Bednar, L. Johansson and A. Satherberg, LET spectra of secondary particles in CR 39 track etch detectors, Radiation Measurement, 26, 645, (1996).