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Overview on Space Dosimetry

Overview on Space Dosimetry. A. Zanini INFN, Via P. Giuria 1, 10125 Torino, Italy. Outline. DEEP SPACE Space radiation risks Cosmic radiation Dosimetry Cautions. Outline. HIGH ALTITUDE COMMERCIAL FLIGHT Secondary radiation Altitude and geomagnetic effects In flight dosimetry

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Overview on Space Dosimetry

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  1. Overview on Space Dosimetry A. Zanini INFN, Via P. Giuria 1, 10125 Torino, Italy A. Zanini – zanini@to.infn.it -

  2. Outline DEEP SPACE • Space radiation risks • Cosmic radiation • Dosimetry • Cautions A. Zanini – zanini@to.infn.it -

  3. Outline HIGH ALTITUDE COMMERCIAL FLIGHT • Secondary radiation • Altitude and geomagnetic effects • In flight dosimetry • Antropomorphic phantom Jimmy A. Zanini – zanini@to.infn.it -

  4. Space exploration Long time permanence on ISS First human Mars exploration A. Zanini – zanini@to.infn.it -

  5. … but In space and in a space station, respectively, as well as in high altitude aircraft, humans are exposed to a complex mixed radiation field. A. Zanini – zanini@to.infn.it -

  6. Radiation risk during space missions ACUTE EFFECTSmore immediately-seen effects of radiation can affect the performance astronauts  (skin-reddening, vomiting/nausea and dehydration).  LONG TERM EFFECTSGiven that only moderate doses of radiation are encountered (and thus acute effects are not seen) the long-term effects of radiation become the most important to consider.  The passage of an energetic charged particle through a cell produces a region of dense ionization along its track.  The ionization can damage DNA molecules near the particle path but a "direct" effect is breaks in  DNA strands.  Single strand breaks (SSB) are quite common and Double Strand Breaks (DSB) are less common.  A. Zanini – zanini@to.infn.it -

  7. Occupational Radiation levels Ref: Health Protection Branch., “1998 Report on Occupational Exposures in Canada”, Environmental Health directorate. A. Zanini – zanini@to.infn.it -

  8. Radiation levels during space missions Measured or estimated radiation levels during space missions (maximum values are reported in parenthesis). Ref.: M. Durante “Radiation protection in space”, La Rivista del Nuovo Cimento, 25-4-8 (2002). A. Zanini – zanini@to.infn.it -

  9. What is the space radiation? The Space Radiation Environment is divided in two components: The primary cosmic radiation(95% protons, 3,5% a particles, HZE nuclei) • geomagnetically trapped radiation • solar particle event radiation (SCR) • galactic cosmic radiation(GCR) The secondary radiation (charged particles, neutrons, gamma- and X-rays) derives from interaction processes with matter, e.g. the hull of a spacecraft, which transforms the primary space radiation into secondary radiation. A. Zanini – zanini@to.infn.it -

  10. Primary radiation Geomagnetically Trapped Radiation (Van Allen Belts)consists of electrons with E > 0.5 MeV, protons with E > 10 MeV and a few helium nuclei. Over the south atlantic region, the geomagnetic field draws particles closer to the earth. This region is known as the South Atlantic Anomaly(SAA). At an orbit below an altitude of about 550 km a considerable part of absorbed radiation dose is caused by passing the SAA (about 30 % in the space station MIR). A. Zanini – zanini@to.infn.it -

  11. Primary radiation Solar particle-event radiations (SPE) are in general large clouds of charged particles (mainly protons and helium nuclei in a wide range of energy) released from the sun by gigantic eruptions during solar storms. During the Apollo programme, it was estimated that one of the largest solar particle-events on record (August 4-9, 1972). Radiation doses to the crew inside the thinly shielded lunar module or during extravehicular activities during such an event would have been extremely serious. A. Zanini – zanini@to.infn.it -

  12. Primary radiation Galactic Cosmic Radiation (GCR)consists of completely ionised atomic nuclei (from protons up to high Z). Heavy Charged Particles (HCP) have their origin outside the solar system and are accelerated to extremely high energies. Average dose rates in absence of geomagnetic shielding are about 15 µGy/h and vary by a factor of 2 with the solar cycle because of solarmagnetic shielding of the central planets. J.A. Simpson, Ann. Rev. Nucl. and Part. Sci. 33, 323 (1983). A. Zanini – zanini@to.infn.it -

  13. Secondary radiation Interaction processes with matter, mainly nuclear fragmentation from cascade processes, transformtheprimary space radiation into secondary radiation. In a similar way, interaction of the primary cosmic radiation with the atoms and molecules of the atmosphere produces a broad spectrum of different secondary particles. A. Zanini – zanini@to.infn.it -

  14. Quantities for radiological protection Absorbed dose D (gray) (1Gy = 1 J/kg) Mean energy imparted by ionising radiation to matter of mass dm LET (J/m) Lineal energy transfert is the quotient of dE by dl, dE is the mean energy lost by the particles, owing to collision with electron, in traversing a distance dL Dose equivalent H (sievert, Sv) (1Sv = 1 Gy* #) Product of D and Q (quality factor at a point in tissue). Q is calculated using the LET of the radiation considered. A. Zanini – zanini@to.infn.it -

  15. Quantities for radiological protection T = tissue or organs DT,R= absorbed dose over the tissue or organ wR = radiation weighting factor R = type of radiation Equivalent dose at tissues (sievert, Sv) HT = equivalent dose wT = tissue weighting factor Effective dose (sievert, Sv) A. Zanini – zanini@to.infn.it -

  16. Dose distribution of space radiation Relative contribution of different components of space radiation to the dose. The equivalent dose is evaluated at the skin, assuming exposure during the solar minimum behind a 5 g/cm2 aluminum shield. (ref. NASA: Strategic Program Plan for Space Radiation Health Research (1998)) A. Zanini – zanini@to.infn.it -

  17. Dose assessment in space • Absorbed dose using TLD • LET spectrum from TEPC • Q mean value definition from LET spectrum • H = Q * D • Risk assessment from H as in NCRP 98 (1989) and NCRP 132 (2000) A. Zanini – zanini@to.infn.it -

  18. Dosimetry in LEO orbit Low Earth Orbit (LEO) is any Earth orbit up to 1,500 kilometers in altitude. LEO crews (as MIR and ISS) are exposed mostly to the trapped proton and GCR. A. Zanini – zanini@to.infn.it -

  19. Dose prediction for future activities A. Zanini – zanini@to.infn.it -

  20. Uncertainties in predicting • The uncertainty in the prediction of the number, kind, and energy of particles predicted to be present in the space radiation environment • The uncertainty in the number, kind, and energy of particles predicted to be present inside any shielded space environment (spacecraft, the ISS, planetary surface, and so on) and inside the tissues of crew members • The uncertainty in the relationship between risk endpoint (for example, excess cancer) and the calculated dose equivalent in the space environment • The uncertainty in the quality factor from the different LET of the HZE particles, which leads to significantly different biological effects for equal doses of different particles A. Zanini – zanini@to.infn.it -

  21. Risk mitigation A number of approaches could reduce the potential radiation-induced health risks in space-flight expectation for each area to contribute to increases in the number of safe days in space where high confidence levels are assured and which will allow NASA to reach its goal of the safe exploration of space. NASA/T-2002–210777 “Space Radiation Cancer Risk Projections for Exploration Missions: Uncertainty Reduction and Mitigation” A. Zanini – zanini@to.infn.it -

  22. Operational Approaches Operational approaches include using the knowledge of the radiation environment to reduce exposures, including selecting the launch time within the solar cycle and the landing site on the Mars surface, and assuring adequate warning and protection from SPE. A. Zanini – zanini@to.infn.it -

  23. Shielding Shielding is potentially a very useful approach to risk mitigation. The use of materials of low atomic mass and high hydrogen content are the key to shielding effectiveness because low-atomic mass materials reduce the occurrence of secondary particle production and are more effective per unit mass of material in slowing down and stopping heavy ions in atomic collisions. Organ Dose Equivalent in Aluminum and Polyethylene Structures for the August 1972 SPE (ref. Wilson, J.W., et al., Shielding from Solar Particle Event Exposures in Deep Space., Radiat. Meas. 30, 361-382, 1999a) A. Zanini – zanini@to.infn.it -

  24. Radioprotectors: drugs and diets • Fruits and vegetables may become as important on space-going vessels as limes were on the sea-going vessels of old. • Radioprotectors can act by different effects: scavenging of free-radicals, induced hypoxia, hydrogen donation to carbon-centred radicals, genome stabilization, physiological or immunological effects A. Zanini – zanini@to.infn.it -

  25. Secondary radiationin atmosphere It is produced by interaction of primary cosmic rays with atmospheric nuclei (O and N); The atmospheric cascade is characterized by: 1. N component(nucleonic component) particles subjected to strong interaction 2. Soft component(electromagnetic component) electrons, positrons end electromagnetic quanta 3. Hard component(muon component). A. Zanini – zanini@to.infn.it -

  26. Influence factors on air shower cascade characteristics: 1. Solar activity Solar surface is periodically characterized by outstanding events (solar flares, Coronal Mass Ejections, Filament Disruptions). The solar activity is described by sunspot numbers, characterized by an 11-year cycle. Higher solar activity = Lower cosmic ray flux on Earth A. Zanini – zanini@to.infn.it -

  27. 2. Geomagnetic field Influence factors on air shower cascade characteristics: Ionized particles of primary cosmic rays are subjected to the Earth magnetic field. The shielding effect of the geomagnetic field is a reduction in the particles intensity when moving from the pole toward the equator. 3. Altitude The build-up of the secondary particles competes with their reduction by the attenuation in the atmosphere. A maximum in the intensity of ionized particles in reached at about 20 km, known as Pfotzer maximum. A. Zanini – zanini@to.infn.it -

  28. Solar Flares A solar flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released involving huge magnetic loops called prominences. Solar flares emit radiation throughout virtually the entire electromagnetic spectrum, including radio waves at long wavelength’s, optical emission, x-rays and gamma rays at short wavelength’s. Measured doses for 10 flights on three different paths at different solar activity levels: FRA-NRT: Franckfurt-Tokyo Narita Airport LHR-NYC: London Heathrow International Airport -New York City LHR-ANC: London Heathrow International Airport -Anchorage J. Wilson, Overview of Radiation Environments and Human Exposures, NASA Langley Research Center (2000). A. Zanini – zanini@to.infn.it -

  29. What about exposure during flights? • Exposure increases with altitude, since the atmosphere absorbs part of the cosmic radiation. Members of flight crews are therefore more subject to exposure than occasional travellers. • As we gain altitude, the protective atmospheric layer grows thinner, increasing our exposure to cosmic radiation.At the cruising altitude of commercial aircraft (10,000 to 12,000 m) the cosmic radiation is approximately 100 to 300 times more intense than at sea level. On board the Concorde (18,000 m) the rate of exposure is almost twice as high as on subsonic planes. • Because of the barrier provided by the earth's magnetic field, there are more particles of cosmic radiation at higher latitudes, closer to the poles, than there are at the equator. A. Zanini – zanini@to.infn.it -

  30. …some data For a given flight, the total dose of cosmic radiation received is directly proportional with the duration of exposure, and thus with the duration of the flight.Measurements taken on board aircraft during the 1990s showed that flight personnel (on long haul flights) receive an average dose of approximately the same magnitude as the one due to exposure to natural radioactivity in France. A. Zanini – zanini@to.infn.it -

  31. World map of airplane routes Dose equivalent rate (mSv/h) A. Zanini – zanini@to.infn.it -

  32. European regulation The 13 May 1996 European EURATOM directive n° 96-29 significantly modified the standards for protecting the health of the population and of workers against the dangers resulting from ionising radiation. One of the innovations of the European directive is that it takes into account the exposure to natural radiation. With regard to the protection of flight crews, article 42 provides the following measures:"Each Member State shall take the necessary measures so that companies operating aircraft take into account the exposure to cosmic radiation of flight crews who are likely to be exposed to more than 1 mSv per year. The company shall take the necessary measures in order to- assess the exposure of the relevant personnel,- take the assessed exposure into account when organising work programmes such as to reduce the doses of highly exposed flight personnel,- inform the employees in questions of the possible dangers to their health resulting from their work,- apply article 10 to female flight personnel.” A. Zanini – zanini@to.infn.it -

  33. Pilots and flight assistants • 900 Flight hours per year in Europe • rotation on different routes • dose assessments by computation codes • measures so that companies operating aircraft take into account the exposure to cosmic radiation of flight crews who are likely to be exposed to more than 1 mSv per year (i.e. crews on intercontinental flights) A. Zanini – zanini@to.infn.it -

  34. Jimmy Phantom The anthropomorphic phantom Jimmy has been designed and realized by INFN Sez. Torino, in collaboration with JRC Varese. It consists of a phantom in polyethylene and plexiglas (tissue equivalent material), with inserted human bone in correspondence of column; composition follows the ICRP indications [1] . Cavities are placed in correspondence of critical organs and are suitable to allocate passive dosemeters such as bubble detectors, TLDs, makrofolds. This system allows to evaluate the neutron dose in depth [1] ICRP -Recommendation of the International Commission on Radiological Protection, Pub. n.60, Oxford Pergamon (1991) A. Zanini – zanini@to.infn.it -

  35. Jimmy Phantom Advantages Applications • Cheap and easy-to-hand phantom • Possibility to obtain an evaluation of the neutron dose in critical organs • The holes can be used to contain different detectors (TLDs, bubble dosemeters, polycarbonate foils) • It can be used for biological samples irradiations. • Exposure under linear accelerators • Calibration of personal dosemeters (JRC Second Standard Laboratory for calibration of personal dosemeters; Ispra, VA) • Dosimetric measurements of cosmic ray neutron: intercontinental flights; high mountains Lab.; balloon flights. A. Zanini – zanini@to.infn.it -

  36. Jimmy Phantom • Main physical characteristics: • Total weight: 37.1 kg • 6 plexiglas slabs (21.6 kg) • 8% H, 32% C, 60% O • 1 big polyethylene slab (14.2 kg) • 14.4% H, 85.6% C • 1 human bone insert (1.2 kg) • 0.2% H, 41.4% O, 18.5% P, 39.9%Ca • to simulate the spinal column • Physical dimensions: • head: 13.5x15x19 cm3 • neck: 11x10x13.5 cm3 • trunk: height 59 cm, max width 36 cm, thickness 20 cm A. Zanini – zanini@to.infn.it -

  37. Measurements (INFN - ALITALIA - ASI projects) • Alitalia flights • Roma-Tokyo • 41° 48’ N 12° 14’ E - 35° 78’ N 140° 32’ E • hmean= 10649 m • Roma - Buenos Aires • 41° 48’ N 12° 14’ E - 34° 49’ S 58° 32’ W • hmean= 10433 m 2. High mountain laboratory Plateau Rosa, Testa Grigia Laboratory h=3480 m, 45° 56’ N, 7° 42’ E 3. ASI balloon flights Trapani-Sevilla hmax= 38000m hmean= 29400m A. Zanini – zanini@to.infn.it -

  38. Neutron spectrumIntercontinental Alitalia flights A. Zanini – zanini@to.infn.it -

  39. Dose at organs Tokyo – Rome path comparison between experimentalBD100R H ratesat organ position and H rates calculated with MCNP4B transport of the measured (BDS) spectrum in the phantom simulation comparison between experimentalBD100R H ratesat organ position andHTrates obtained folding the measured spectrum with ICRP74 conv. coeff. (DT/F and wr). A. Zanini – zanini@to.infn.it -

  40. Dose at organs Buenos Aires – Rome path comparison between experimentalBD100R H ratesat organ position andHTrates obtained folding the measured spectrum with ICRP74 conv. coeff. (DT/F and wr). comparison between experimentalBD100R H ratesat organ position and H rates calculated with MCNP4B transport of the measured (BDS) spectrum in the phantom simulation A. Zanini – zanini@to.infn.it -

  41. Jimmy exposures at other altitudes Testa Grigia research station (3480 m) BREUIL – CERVINIA (ITALY) 45°56’03” N, 07°42’28” E BIRBA ASI flight Trapani-Sevilla Max. altitude 38000 m Mean Alt. 29400 m A. Zanini – zanini@to.infn.it -

  42. Comparison at different altitudes Measured organ dose rates Approximated effective dose rates A. Zanini – zanini@to.infn.it -

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