ICRP Publication 123
Assessment of Radiation Exposure of Astronauts in Space
Recommended citation
ICRP, 2013. Assessment of Radiation Exposure of Astronauts in Space. ICRP Publication 123. Ann. ICRP 42(4).
Authors on behalf of ICRP
G. Dietze, D.T. Bartlett, D.A. Cool, F.A. Cucinotta, X. Jia, I.R. McAulay, M. Pelliccioni, V. Petrov, G. Reitz, T. Sato
Abstract - During their occupational activities in space, astronauts are exposed to ionising radiation from natural radiation sources present in this environment. They are, however, not usually classified as being occupationally exposed in the sense of the general ICRP system for radiation protection of workers applied on Earth. The exposure assessment and risk-related approach described in this report is clearly restricted to the special situation in space, and should not be applied to any other exposure situation on Earth. The report describes the terms and methods used to assess the radiation exposure of astronauts, and provides data for the assessment of organ doses. Chapter 1 describes the specific situation of astronauts in space, and the differences in the radiation fields compared with those on Earth. In Chapter 2, the radiation fields in space are described in detail, including galactic cosmic radiation, radiation from the Sun and its special solar particle events, and the radiation belts surrounding the Earth. Chapter 3 deals with the quantities used in radiological protection, describing the Publication 103 system of dose quantities, and subsequently presenting the special approach for applications in space; due to the strong contribution of heavy ions in the radiation field, radiation weighting is based on the radiation quality factor, Q, instead of the radiation weighting factor, wR. In Chapter 4, the methods of fluence and dose measurement in space are described, including instrumentation for fluence measurements, radiation spectrometry, and area and individual monitoring. The use of biomarkers for the assessment of mission doses is also described. The methods of determining quantities describing the radiation fields within a spacecraft are given in Chapter 5. Radiation transport calculations are the most important tool. Some physical data used in radiation transport codes are presented, and the various codes used for calculations in high-energy radiation fields in space are described. Results of calculations and measurements of radiation fields in spacecraft are given. Some data for shielding possibilities are also presented. Chapter 6 addresses methods of determining mean absorbed doses and dose equivalents in organs and tissues of the human body. Calculated conversion coefficients of fluence to mean absorbed dose in an organ or tissue are given for heavy ions up to Z = 28 for energies from 10 MeV/u to 100 GeV/u. For the same set of ions and ion energies, mean quality factors in organs and tissues are presented using, on the one hand, the Q(L) function defined in Publication 60, and, on the other hand, a Q function proposed by the National Aeronautics and Space Administration. Doses in the body obtained by measurements are compared with results from calculations, and biodosimetric measurements for the assessment of mission doses are also presented. In Chapter 7, operational measures are considered for assessment of the exposure of astronauts during space missions. This includes preflight mission design, area and individual monitoring during flights in space, and dose recording. The importance of the magnitude of uncertainties in dose assessment is considered. Annex A shows conversion coefficients and mean quality factors for protons, charged pions, neutrons, alpha particles, and heavy ions (2 < Z ≤ 28), and particle energies up to 100 GeV/u.
© 2013 ICRP. Published by Elsevier Ltd.
Keywords: Radiation fields in space; Protection and operational quantities; Dose measurements; Radiation transport and shielding; Conversion coefficients.
G. DIETZE, D.T. BARTLETT ARTLETT, D.A. COOL, F.A. CUCINOTTA UCINOTTA, X. JIA, I.R. MCAULAY, M. PELLICCIONI ELLICCIONI, V. PETROV, G. REITZ, T. SATO
Key Points
In space, astronauts are exposed to ionising radiation from natural radiation sources that are always present in this environment. Although these exposures occur in the context of their occupation, astronauts – due to their exceptional exposure situation – are not usually classified as being occupationally exposed in the sense of the general ICRP system for radiation protection of workers applied on Earth or for aircraft crews. The different – more risk-related – concept of exposure assessment described in this report is clearly restricted to the special situation in space, and should not be applied to any other exposure situation on Earth or for aircraft crews.
The radiation field that astronauts are exposed to in space is very complex. It contains electrons, protons, alpha particles, and heavier ions up to very high energies from galactic cosmic radiation, protons and electrons emitted from the Sun, protons and electrons trapped in belts by the magnetic field of the Earth, and various secondary radiations including neutrons created by interactions between primary radiation and materials of the spacecraft. Doses of astronauts in space are significant fractions of a mSv day-1 and, depending on the time spent in space, mission doses to astronauts may far exceed 100 mSv. Only external radiation exposure to astronauts needs to be considered.
Due to the specifics of the radiation field in space, not all concepts of quantities defined for radiological protection applications on Earth are appropriate for applications in space missions, especially when risk assessment is an important task. A radiation weighting factor (wR) of 20 for all types and energies of heavy ions in the definition of equivalent dose is not justified. For heavy ions, the ratio of wR and mean quality factors averaged over the human body is up to 10 depending on the type and energy of the ion.
No specific operational dose quantity is recommended for area monitoring in space. Quantities to be measured are radiation fluence rates, the energy distributions of different types of particles, and linear energy transfer (LET) distributions. For individual monitoring, measurement of absorbed dose at the surface of the body in combination with LET distributions may be appropriate for an assessment of effective dose equivalent or organ dose equivalent.
Radiation transport calculations are important tools for information about radiation exposure of astronauts. Based on data about the primary radiation fields, transport calculations are able to calculate radiation fields inside a spacecraft, on the body of astronauts, and in organs or tissues of anthropomorphic phantoms.
Generally, two different procedures may be applied for the assessment of doses in the astronaut’s body by calculations. One may either assess the radiation field parameters near to an astronaut and then apply fluence to dose conversion coefficients for all types of particles involved for the assessment of organ doses, or one may calculate organ doses in a body using the radiation field data outside of the spacecraft and a code that combines radiation transport into the spacecraft and into the human body. Measurements with individual dosimeters near to the body of an astronaut, in combination with calculations, may be directly correlated to doses in the human body.
This report presents conversion coefficients for mean absorbed doses in organs and tissues of the body for heavy ions up to Z = 28. The calculations are based on the reference voxel phantoms following the 2007 Recommendations of ICRP (ICRP, 2007). Data are given for isotropic exposure of the body. Also, mean quality factors, QT, for the specified organs and tissues of the body are presented. QT values vary between approximately 2 and 25.
Information and data are also presented for the quality factor concept derived from the track structure of charged particles in tissue as proposed by the National Aeronautics and Space Administration (Cucinotta et al., 2011). This results in a different distribution of Q in terms of LET with a stronger decrease in Q with increasing LET.
Executive Summary
(a) Astronauts live and work in low Earth orbits for extended periods of time, especially during the operation and maintenance of the International Space Station (ISS) and scientific investigations. Furthermore, plans have already been discussed for deep space missions of astronauts.
(b) Publication 103 (ICRP, 2007) stated that ‘Exceptional cases of cosmic radiation exposures, such as exposure in space travel, where doses may be significant and some type of control warranted, should be dealt with separately from the conventional approach of occupational exposure’. Therefore, although in space, astronauts are exposed to ionising radiation from natural radiation sources which are always present in this environment during their occupational activities, their exposure is not usually classified as occupational in the sense of the general ICRP system for radiation protection of workers applied on Earth and for aircraft crew. The exposure assessment and risk-related approach described in this report is clearly restricted to the special situation in space and should not be applied to any other exposure situation on Earth. This report demonstrates this exceptional situation, describes the terms and methods used to assess the radiation exposure of astronauts, and provides data for the assessment of organ doses.
(c) This report contains seven chapters. Chapter 1 describes the specific situation of astronauts in space, and the differences between radiation fields in space and on Earth, thereby showing areas where approaches applied in radiological protection measures on Earth need to be modified.
(d) In Chapter 2, the radiation fields in space are described in detail. The solar system with the Sun at its centre is embedded in a complex mixture of galactic cosmic radiation (GCR) – protons, alpha particles, and heavy ions – that enters the heliosphere continuously from all directions. Inside the heliosphere, the GCR fluence rate and particle energy distributions are modulated by the interplanetary magnetic field produced by the charged particles emitted continuously by the Sun, the so-called ‘solar wind’. In addition to the solar wind, the Sun occasionally emits unusually large pulses of energetic particles – mainly protons and electrons – called ‘solar particle events’ (SPEs). Celestial bodies equipped with a magnetic moment like the Earth are surrounded by toroidal belts of particulate radiation. Such radiation belts constitute an important third source of primary exposure. Fluence rates of cosmic radiation are not constant; they vary between two extremes which correspond in time with maximum and minimum solar activity. Solar activity and cosmic radiation fluence rates are inversely correlated. In Sections 2.2–2.5, the various components of the radiation field in space are presented and the influence of the Earth’s magnetic field is described.
(e) Chapter 3 deals with the quantities used in radiological protection. The system of dose quantities as given in Publication 103 (ICRP, 2007) is described and relative biological effectiveness is discussed, especially with respect to the large contribution of heavy ions and the very high energies. A single wR value of 20 for all heavy ions of all energies is not appropriate for space radiation fields. Hence, for space applications, the concept of a quality factor, Q(L), is also applied to the protection quantities. The approach for applications in space is described in detail in Section 3.3.
(f) In Chapter 4, the methods of fluence and dose measurements in space are described. These include instrumentation for fluence measurements, radiation spectrometry, area dosimetry, and individual monitoring. Passive and active devices are mentioned, and the use of biomarkers for the assessment of mission doses is described. Some advice for quality control and the assessment of uncertainties is also given in this chapter.
(g) In Chapter 5, the methods of determining quantities describing the radiation fields within a spacecraft are given. Radiation transport calculations are the most important tool for the assessment of radiation fields inside a spacecraft, starting from the radiation field in free space and considering the walls and equipment in the spacecraft. In this chapter, some physical data used in radiation transport codes are presented, and the various codes used for calculations in high-energy radiation fields are described. Results of calculations of radiation fields in spacecraft are given. A discussion of shielding possibilities is also included in this chapter.
(h) Chapter 6 addresses methods of determining mean absorbed doses and dose equivalents in organs and tissues of the human body. Calculated conversion coefficients of fluence to mean absorbed dose in an organ or tissue are given for heavy ions up to Z = 28 for energies from 10 MeV/u to 100 GeV/u. For the same set of ions and ion energies, mean quality factors in organs and tissues are presented using, on the one hand, the Q(L) function defined in Publication 60 (ICRP, 1991) and, on the other hand, a Q(Z,E) function proposed by the National Aeronautics and Space Administration (Cucinotta et al., 2011). Assessment of doses in the body by measurements are described in Section 6.4, and results are compared with calculations. Biodosimetric measurements for the assessment of mission doses are presented in Section 6.5.
(i) In Chapter 7, operational measures are considered for assessment of the exposure of astronauts during space missions. This includes preflight mission design, area and individual monitoring during flights in space, and dose recording. The importance of considering uncertainties in dose assessment is also mentioned.
(j) Annex A provides conversion coefficients and mean quality factors for protons, charged pions, neutrons, alpha particles, and heavy ions (2 < Z ≤ 28).
ICRP, 2013. Assessment of Radiation Exposure of Astronauts in Space. ICRP Publication 123. Ann. ICRP 42(4).
Authors on behalf of ICRP
G. Dietze, D.T. Bartlett, D.A. Cool, F.A. Cucinotta, X. Jia, I.R. McAulay, M. Pelliccioni, V. Petrov, G. Reitz, T. Sato
Abstract - During their occupational activities in space, astronauts are exposed to ionising radiation from natural radiation sources present in this environment. They are, however, not usually classified as being occupationally exposed in the sense of the general ICRP system for radiation protection of workers applied on Earth. The exposure assessment and risk-related approach described in this report is clearly restricted to the special situation in space, and should not be applied to any other exposure situation on Earth. The report describes the terms and methods used to assess the radiation exposure of astronauts, and provides data for the assessment of organ doses. Chapter 1 describes the specific situation of astronauts in space, and the differences in the radiation fields compared with those on Earth. In Chapter 2, the radiation fields in space are described in detail, including galactic cosmic radiation, radiation from the Sun and its special solar particle events, and the radiation belts surrounding the Earth. Chapter 3 deals with the quantities used in radiological protection, describing the Publication 103 system of dose quantities, and subsequently presenting the special approach for applications in space; due to the strong contribution of heavy ions in the radiation field, radiation weighting is based on the radiation quality factor, Q, instead of the radiation weighting factor, wR. In Chapter 4, the methods of fluence and dose measurement in space are described, including instrumentation for fluence measurements, radiation spectrometry, and area and individual monitoring. The use of biomarkers for the assessment of mission doses is also described. The methods of determining quantities describing the radiation fields within a spacecraft are given in Chapter 5. Radiation transport calculations are the most important tool. Some physical data used in radiation transport codes are presented, and the various codes used for calculations in high-energy radiation fields in space are described. Results of calculations and measurements of radiation fields in spacecraft are given. Some data for shielding possibilities are also presented. Chapter 6 addresses methods of determining mean absorbed doses and dose equivalents in organs and tissues of the human body. Calculated conversion coefficients of fluence to mean absorbed dose in an organ or tissue are given for heavy ions up to Z = 28 for energies from 10 MeV/u to 100 GeV/u. For the same set of ions and ion energies, mean quality factors in organs and tissues are presented using, on the one hand, the Q(L) function defined in Publication 60, and, on the other hand, a Q function proposed by the National Aeronautics and Space Administration. Doses in the body obtained by measurements are compared with results from calculations, and biodosimetric measurements for the assessment of mission doses are also presented. In Chapter 7, operational measures are considered for assessment of the exposure of astronauts during space missions. This includes preflight mission design, area and individual monitoring during flights in space, and dose recording. The importance of the magnitude of uncertainties in dose assessment is considered. Annex A shows conversion coefficients and mean quality factors for protons, charged pions, neutrons, alpha particles, and heavy ions (2 < Z ≤ 28), and particle energies up to 100 GeV/u.
© 2013 ICRP. Published by Elsevier Ltd.
Keywords: Radiation fields in space; Protection and operational quantities; Dose measurements; Radiation transport and shielding; Conversion coefficients.
G. DIETZE, D.T. BARTLETT ARTLETT, D.A. COOL, F.A. CUCINOTTA UCINOTTA, X. JIA, I.R. MCAULAY, M. PELLICCIONI ELLICCIONI, V. PETROV, G. REITZ, T. SATO
Key Points
In space, astronauts are exposed to ionising radiation from natural radiation sources that are always present in this environment. Although these exposures occur in the context of their occupation, astronauts – due to their exceptional exposure situation – are not usually classified as being occupationally exposed in the sense of the general ICRP system for radiation protection of workers applied on Earth or for aircraft crews. The different – more risk-related – concept of exposure assessment described in this report is clearly restricted to the special situation in space, and should not be applied to any other exposure situation on Earth or for aircraft crews.
The radiation field that astronauts are exposed to in space is very complex. It contains electrons, protons, alpha particles, and heavier ions up to very high energies from galactic cosmic radiation, protons and electrons emitted from the Sun, protons and electrons trapped in belts by the magnetic field of the Earth, and various secondary radiations including neutrons created by interactions between primary radiation and materials of the spacecraft. Doses of astronauts in space are significant fractions of a mSv day-1 and, depending on the time spent in space, mission doses to astronauts may far exceed 100 mSv. Only external radiation exposure to astronauts needs to be considered.
Due to the specifics of the radiation field in space, not all concepts of quantities defined for radiological protection applications on Earth are appropriate for applications in space missions, especially when risk assessment is an important task. A radiation weighting factor (wR) of 20 for all types and energies of heavy ions in the definition of equivalent dose is not justified. For heavy ions, the ratio of wR and mean quality factors averaged over the human body is up to 10 depending on the type and energy of the ion.
No specific operational dose quantity is recommended for area monitoring in space. Quantities to be measured are radiation fluence rates, the energy distributions of different types of particles, and linear energy transfer (LET) distributions. For individual monitoring, measurement of absorbed dose at the surface of the body in combination with LET distributions may be appropriate for an assessment of effective dose equivalent or organ dose equivalent.
Radiation transport calculations are important tools for information about radiation exposure of astronauts. Based on data about the primary radiation fields, transport calculations are able to calculate radiation fields inside a spacecraft, on the body of astronauts, and in organs or tissues of anthropomorphic phantoms.
Generally, two different procedures may be applied for the assessment of doses in the astronaut’s body by calculations. One may either assess the radiation field parameters near to an astronaut and then apply fluence to dose conversion coefficients for all types of particles involved for the assessment of organ doses, or one may calculate organ doses in a body using the radiation field data outside of the spacecraft and a code that combines radiation transport into the spacecraft and into the human body. Measurements with individual dosimeters near to the body of an astronaut, in combination with calculations, may be directly correlated to doses in the human body.
This report presents conversion coefficients for mean absorbed doses in organs and tissues of the body for heavy ions up to Z = 28. The calculations are based on the reference voxel phantoms following the 2007 Recommendations of ICRP (ICRP, 2007). Data are given for isotropic exposure of the body. Also, mean quality factors, QT, for the specified organs and tissues of the body are presented. QT values vary between approximately 2 and 25.
Information and data are also presented for the quality factor concept derived from the track structure of charged particles in tissue as proposed by the National Aeronautics and Space Administration (Cucinotta et al., 2011). This results in a different distribution of Q in terms of LET with a stronger decrease in Q with increasing LET.
Executive Summary
(a) Astronauts live and work in low Earth orbits for extended periods of time, especially during the operation and maintenance of the International Space Station (ISS) and scientific investigations. Furthermore, plans have already been discussed for deep space missions of astronauts.
(b) Publication 103 (ICRP, 2007) stated that ‘Exceptional cases of cosmic radiation exposures, such as exposure in space travel, where doses may be significant and some type of control warranted, should be dealt with separately from the conventional approach of occupational exposure’. Therefore, although in space, astronauts are exposed to ionising radiation from natural radiation sources which are always present in this environment during their occupational activities, their exposure is not usually classified as occupational in the sense of the general ICRP system for radiation protection of workers applied on Earth and for aircraft crew. The exposure assessment and risk-related approach described in this report is clearly restricted to the special situation in space and should not be applied to any other exposure situation on Earth. This report demonstrates this exceptional situation, describes the terms and methods used to assess the radiation exposure of astronauts, and provides data for the assessment of organ doses.
(c) This report contains seven chapters. Chapter 1 describes the specific situation of astronauts in space, and the differences between radiation fields in space and on Earth, thereby showing areas where approaches applied in radiological protection measures on Earth need to be modified.
(d) In Chapter 2, the radiation fields in space are described in detail. The solar system with the Sun at its centre is embedded in a complex mixture of galactic cosmic radiation (GCR) – protons, alpha particles, and heavy ions – that enters the heliosphere continuously from all directions. Inside the heliosphere, the GCR fluence rate and particle energy distributions are modulated by the interplanetary magnetic field produced by the charged particles emitted continuously by the Sun, the so-called ‘solar wind’. In addition to the solar wind, the Sun occasionally emits unusually large pulses of energetic particles – mainly protons and electrons – called ‘solar particle events’ (SPEs). Celestial bodies equipped with a magnetic moment like the Earth are surrounded by toroidal belts of particulate radiation. Such radiation belts constitute an important third source of primary exposure. Fluence rates of cosmic radiation are not constant; they vary between two extremes which correspond in time with maximum and minimum solar activity. Solar activity and cosmic radiation fluence rates are inversely correlated. In Sections 2.2–2.5, the various components of the radiation field in space are presented and the influence of the Earth’s magnetic field is described.
(e) Chapter 3 deals with the quantities used in radiological protection. The system of dose quantities as given in Publication 103 (ICRP, 2007) is described and relative biological effectiveness is discussed, especially with respect to the large contribution of heavy ions and the very high energies. A single wR value of 20 for all heavy ions of all energies is not appropriate for space radiation fields. Hence, for space applications, the concept of a quality factor, Q(L), is also applied to the protection quantities. The approach for applications in space is described in detail in Section 3.3.
(f) In Chapter 4, the methods of fluence and dose measurements in space are described. These include instrumentation for fluence measurements, radiation spectrometry, area dosimetry, and individual monitoring. Passive and active devices are mentioned, and the use of biomarkers for the assessment of mission doses is described. Some advice for quality control and the assessment of uncertainties is also given in this chapter.
(g) In Chapter 5, the methods of determining quantities describing the radiation fields within a spacecraft are given. Radiation transport calculations are the most important tool for the assessment of radiation fields inside a spacecraft, starting from the radiation field in free space and considering the walls and equipment in the spacecraft. In this chapter, some physical data used in radiation transport codes are presented, and the various codes used for calculations in high-energy radiation fields are described. Results of calculations of radiation fields in spacecraft are given. A discussion of shielding possibilities is also included in this chapter.
(h) Chapter 6 addresses methods of determining mean absorbed doses and dose equivalents in organs and tissues of the human body. Calculated conversion coefficients of fluence to mean absorbed dose in an organ or tissue are given for heavy ions up to Z = 28 for energies from 10 MeV/u to 100 GeV/u. For the same set of ions and ion energies, mean quality factors in organs and tissues are presented using, on the one hand, the Q(L) function defined in Publication 60 (ICRP, 1991) and, on the other hand, a Q(Z,E) function proposed by the National Aeronautics and Space Administration (Cucinotta et al., 2011). Assessment of doses in the body by measurements are described in Section 6.4, and results are compared with calculations. Biodosimetric measurements for the assessment of mission doses are presented in Section 6.5.
(i) In Chapter 7, operational measures are considered for assessment of the exposure of astronauts during space missions. This includes preflight mission design, area and individual monitoring during flights in space, and dose recording. The importance of considering uncertainties in dose assessment is also mentioned.
(j) Annex A provides conversion coefficients and mean quality factors for protons, charged pions, neutrons, alpha particles, and heavy ions (2 < Z ≤ 28).
