Recent Observations of Space Radiation Characteristics in a Tissue- Equivalent Phantom onboard International Space Station by Liulin-5 Dosemetric Telescope J. Semkova 1, R. Koleva 1, S. Maltchev 1, N. Bankov 1, V. Benghin 2, I. Chernykh 2, V. Shurshakov 2, V. Petrov 2, S. Drobyshev 2 1 Space Research and Technologies Institute, Bulgarian Academy of Sciences, 2 Institute of Biomedical Problems, Russian Academy of RAD 2012, Nis, Serbia, 24 – 28 April, 2012

 Ionizing radiation is a main health concern to the astronauts in long duration space flights.  Complex ISS radiation environment –GCR, trapped radiation, SEP, and the secondary radiation produced in the shielding materials of the spacecraft and in human body. Very dangerous is high energy heavy ion component of GCR, with high LET and highly penetrating in human body, with a large potential for radiobiological damage.  Dose characteristics in LEO depend also on the solar cycle phase, spacecraft orbit parameters, helio – and geophysical parameters.  To estimate the organ doses measurements in phantoms are conducted on ISS –Matroshka and Matroshka –R projects. MOTIVATION

Radiation sources in the Earth environment  GCRs-99% protons and He nuclei, 1% heavy ions, energies up to tens of GeV/n -permanent source of ionising radiation, isotropic.  Protons IERB - hundreds of MeV, directionality; electrons OERB- hundreds of keV.  SPE- hundreds of MeV.

South Atlantic Anomaly A LEO spacecraft encounters the inner radiation belt protons in the region of South Atlantic Anomaly (SAA). Although only about 5% of ISS mission time is spent in the SAA, the astronauts may collect more than 50% of their total absorbed dose during this short time period (Apathy et al., 2007). SAA forming (Heynderickx, 2002) Dimensions of SAA at 500 km altitude [ gallery/misc_saad.html] gallery/misc_saad.html

Bulgarian space radiation dosimetric instruments and experiments (Dachev etal., 1989, 2006, 2009, 2009a,2010, Semkova et al., 2010, 2011) Bulgarian space radiation dosimetric instruments and experiments (Dachev etal., 1989, 2006, 2009, 2009a, 2010, Semkova et al., 2010, 2011) 1.Liulin- MIR space station, 1988 – Radius –MD1/2 on Mars-96; 3.Liulin-MDU1, June 14, 2000, ESA balloon flight up to 33 km over Gap, France; 4.Liulin-MDU5, more than hours from 2001 till 2009 on Czech airlines aircrafts; 5.Liulin-Е094, May-August 2001, ESA-NASA exp. on the International space station (ISS); 6.2 Liulin-MDU, June 2001, NASA ER-2 flights at 20 km altitude in USA; 7.R3D-B1, October 2002, ESA Foton M1 satellite – unsuccessful launch; 8.R3D-B2, , ESA Foton M2 satellite; 9.3 Liulin-MDU, June 11, 2005, NASA balloon flight up to 40 km over New Mexico, USA; 10.Liulin-ISS, ROSCOSMOS, launched to ISS in September 2005 (active now); 11.Liulin-6R, since October 2005 working in Internet (active now); 12.Liulin-Moussala, since June 2006 working in Internet (active now); 13.Liulin-5, ROSCOSMOS, since June 28, 2007 working at ISS (active now); 14.R3D-B3, September , ESA Foton M3 satellite; 15.Liulin-6S, since October 2007 working at Jungfrau peak in Internet (active now); 16.Liulin-R, January 31, 2008, ESA rocket experiment up to 380 km from Norway; 17.R3DЕ, worked at ESA Columbus module at ISS between 17/02/2008 and 01/09/2009; 18.RADOM, worked at Indian Chandrayyan-1 satellite around Moon between 22/10/2008 and 29/08/2009; 19.R3DR, worked at ESA EXPOSE-R facility on Russian Zvezda module of ISS between March 2008 and January Liulin-Phobos launched on 9 November 2011 on Phobos-Grunt interplanetary station.

Since 2005 Bulgarian scientists participate with 15 instruments in the scientific programs of: 4 manned space flights (4 instr.) – 1 at ESA Columbus and 3 at the Russian segment of ISS 1 Moon spacecraft (1 instr.) – Chandrayaan-1 2 spacecrafts (3 instr.) - Foton M2/3 2 HotPay rockets (2 instr.), 1 balloon (1 instr.), flight and many airplane flights (4 instr.) Rocket and balloon instruments Liulin-R Flown on HotPay 2 Rocket in 2008 Liulin-J Flown on NASA Balloon in 2005 Aircraftinstruments Liulin- type flown for more than 6000 hours fn CSA aircraft

Spherical Tissue – Equivalent Phantom and Liulin-5  Size: 370x370x390 mm; mass: 32 kg (Shurshakov, V. A, et al., 2006)  Radiation detectors –number of passive detectors and Liulin-5 charged paricle telescope.  Liulin-5 detector module is placed in a radial channel. Aim of the experiment – to measure the the time resolved depth distribution of the cosmic radiation doses in the phantom.

LIULIN-5 in the Phantom in Piers-1 module of ISS –activated 28 June Spherical Phantom LIulin -5 in the Spherical Phantom on ISS Detector module Phantom

Block - diagram of Liulin - 5 connections in the phantom

Goals  Liulin-5 measures simultaneously at 3 depths of the radial channel of the spherical phantom: Energy Deposition Spectra, Dose Rate & Particle flux - then Absorbed Dose D.  Measurement of the Linear Energy Transfer (LET) spectra in silicon – then assessment of LET(H 2 O), Q=f(LET), given in ICRP-60 and Dose Equivalent H; H=DxQave.

Quality factor

RESULTS   Dose and flux distribution in the radial channel of the phantom.  LET spectra.   Dosemetric quantities from GCR and trapped protons.

Dose rate along the ISS trajectory Dose rates distribution at 60 mm depth ( ), D2  760 µGy/h. Max doses - at L ~ 1.36, В ~ 0.2 Gs.

Flux at the centre of the phantom along the ISS trajectory At L values both GCR and trapped protons contribute to the measured flux. Maximum fluxes of 51.8 part/cm 2 s are registered from the trapped protons in SAA at L ~ Minima values of about 0.12 part/cm 2 s were recorded at L~1 from GCR. At L  4 the particle flux from GCR was up to 2.1 part/cm 2 s.

Absorbed depth-dose distribution and contribution of GCR and trapped protons to the total doses Typical

Data for From top to bottom: 1) LET spectra averaged over the whole interval; 2) GCR and secondary radiation LET spectra averaged outside SAA; 3) LET spectra averaged over measurements in SAA - trapped protons mainly. Due to HZE particles in LET spectra of GCR, the GCR Q is higher than that of the trapped protons. LET spectra and Qav

Absorbed average daily dose at the depth of 40 mm (BFO), Qav and averaged daily dose equivalents from particles of 0.65  LET (H 2 O) Absorbed average daily dose at the depth of 40 mm (BFO), Qav and averaged daily dose equivalents from particles of 0.65  LET (H 2 O) Date Date Dose [µGy/day] Qav Dose equivalent [µSv/day] GCRSAATotalGCRSAATotalGCRSAATotal , ,

CONCLUSION (1)  The averaged absorbed daily doses at the depths corresponding to BFO depths are µGy/day. The contribution of the trapped protons is about 50-60% of the total absorbed doses and the rest of the dose is from the GCR.  Due to the self-shielding of the phantom against trapped protons the absorbed doses at 165 mm depth typically decrease by a factor of compared to the doses at 40 mm depth.  A detailed mapping of the particle flux and dose rate distribution along the ISS orbit is done.

CONCLUSION (2)  Typically Qav from 2007 to 2009 is , the average dose equivalent at the depth of BFO is µSV/day.  At the minimum of the 23rd solar cycle the dose equivalent of GCR and their secondary particles represents  70% of total dose equivalent at the depths of BFO.  Liulin-5 experiment continues in aboard ISS to obtain data for solar activity maximum.

ACKNOWLEDGEMENTS  Agreement between RAS and BAS on space research and grant DID-02/8 from the Bulgarian Science Fund.  NIRS - Japan.  RKK “Energia” and cosmonauts O. Kotov, Y. Malenchenko, O. Kononenko and Y. Lonchakov for the operation of Liulin - 5 aboard ISS.

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