Difference between revisions of "Radiation"

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[[Image:nuclear_warning_sign.png|right|Nuclear Danger Icon]]
 
[[Image:nuclear_warning_sign.png|right|Nuclear Danger Icon]]
 
Natural '''Radiation''' on [[Mars]] is much higher compared with [[Earth]]. The thin [[atmosphere]] provides only a small shielding effect against harmful [[solar radiation]] and [[cosmic radiation]].  Mars also lacks the [[magnetosphere]] that protects Earth.
 
Natural '''Radiation''' on [[Mars]] is much higher compared with [[Earth]]. The thin [[atmosphere]] provides only a small shielding effect against harmful [[solar radiation]] and [[cosmic radiation]].  Mars also lacks the [[magnetosphere]] that protects Earth.
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 +
The average natural radiation level on Mars is 24-30 rads or 240-300 mSv per year(<sub>needs checking and reference</sub>).  This is about 40-50 times the average on Earth.
  
 
Occasional [[solar flares]] produce particularly high doses. Some Solar Proton Events (SPEs) were observed by [[MARIE]] that were not seen by sensors near Earth due to the fact that SPEs are directional. Astronauts on Mars could be warned of SPEs by sensors closer to the Sun and presumably take shelter during these events. This would imply an [[Early warning system (solar radiation)|Early Warning System]] (possibly a network of sensors in orbit around the sun or a single sensor in [[Lagrangian point]] L1) might be needed to ensure all SPEs threatening Mars were detected early enough.  
 
Occasional [[solar flares]] produce particularly high doses. Some Solar Proton Events (SPEs) were observed by [[MARIE]] that were not seen by sensors near Earth due to the fact that SPEs are directional. Astronauts on Mars could be warned of SPEs by sensors closer to the Sun and presumably take shelter during these events. This would imply an [[Early warning system (solar radiation)|Early Warning System]] (possibly a network of sensors in orbit around the sun or a single sensor in [[Lagrangian point]] L1) might be needed to ensure all SPEs threatening Mars were detected early enough.  
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1 millisievert [mSv] = 0.1 rad [rd]
  
 
==Types of Radiation==
 
==Types of Radiation==
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|-
 
|-
 
!Name
 
!Name
!Relative Biological<br /> Effectiveness RBE
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!Relative Biological<br /> Effectiveness (RBE)
 
!Source
 
!Source
 
|-
 
|-
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8.5<br />   
 
8.5<br />   
 
10  
 
10  
|Cosmic rays, inner-radiation belts, and solar [[cosmic rays]]
+
|[[Cosmic radiation]], inner-radiation belts, and [[solar radiation]]
 
|-
 
|-
 
|'''[[neutron|Neutrons]]'''<br />   
 
|'''[[neutron|Neutrons]]'''<br />   
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10.5<br />   
 
10.5<br />   
 
6.4
 
6.4
|Nuclear interactions in the [[sun]]
+
|Nuclear interactions in the [[sun]]; on Mars, produced when [[cosmic radiation]] interacts with [[regolith]]
 
|-
 
|-
 
|'''[[alpha particles|Alpha Particles]]'''<br />   
 
|'''[[alpha particles|Alpha Particles]]'''<br />   
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15<br />   
 
15<br />   
 
20  
 
20  
|Cosmic rays
+
|[[Cosmic radiation]]
 
|-
 
|-
 
|[[Heavy Ions|'''Heavy Ions''']]
 
|[[Heavy Ions|'''Heavy Ions''']]
 
|Varies widely
 
|Varies widely
|Cosmic rays
+
|[[Cosmic radiation]]
 
|}
 
|}
 +
(RBE is a measure of the damage done to living tissue, relative to gamma rays)
 +
 
Cosmic radiation comprises 85% protons, 14% alpha particles, and 1% heavy ions.<ref>Schimmerling W. (2011, Feb 5). The Space Radiation Environment: An Introduction. <nowiki>https://three.jsc.nasa.gov/concepts/SpaceRadiationEnviron.pdf</nowiki></ref>  Solar radiation includes the same radiation types, but it a higher proportion of protons and its heavy primaries have lower energy levels.  The high-energy heavy primaries in cosmic radiation can penetrate materials that effectively block lower-energy radiation<ref name=":1">Rapp D. (2006). Radiation Effects and Shielding Requirements in Human Missions to the Moon and Mars. Mars 2:46-71. <nowiki>https://doi.org/10.1555/mars.2006.0004</nowiki></ref>.
 
Cosmic radiation comprises 85% protons, 14% alpha particles, and 1% heavy ions.<ref>Schimmerling W. (2011, Feb 5). The Space Radiation Environment: An Introduction. <nowiki>https://three.jsc.nasa.gov/concepts/SpaceRadiationEnviron.pdf</nowiki></ref>  Solar radiation includes the same radiation types, but it a higher proportion of protons and its heavy primaries have lower energy levels.  The high-energy heavy primaries in cosmic radiation can penetrate materials that effectively block lower-energy radiation<ref name=":1">Rapp D. (2006). Radiation Effects and Shielding Requirements in Human Missions to the Moon and Mars. Mars 2:46-71. <nowiki>https://doi.org/10.1555/mars.2006.0004</nowiki></ref>.
  
==Danger==
+
==Exposure limits==
Exposure to dangerous levels of radiation causes [[radiation sickness]] and cancer. Any exposure to radiation, no matter how slight, poses some risk. Small dose - small risk of cancer. High dose - high risk of cancer.  The average exposure to  radiation on Earth due to natural sources is 6.2 mSv per year<ref name=":3" />  
+
 
 +
===Limits for humans===
 +
Exposure to dangerous levels of radiation causes [[radiation sickness]] and cancer. Any exposure to radiation, no matter how slight, poses some risk. Small dose - small risk of cancer. High dose - high risk of cancer.  The average exposure to  radiation on Earth due to natural sources is 6.2 mSv per year<ref name=":3">http://www.ans.org/pi/resources/dosechart/msv.php</ref>  
  
 
Nevertheless, there are defined legal limits for exposure during work for several professional activities, such as for X-ray assistants, airplane personnel, etc. The International Commission on Radiation Protection recommends that occupational (work-related) radiation exposure be limited to 50 millisieverts (mSv) per year, and limited to 100 mSv over any 5-year period<ref>http://www.icrp.org/publication.asp?id=ICRP%20Publication%20103</ref>. NASA's radiation dose limits for astronauts are established in NASA-STD-3001<ref>NASA. (2015). <i>NASA Space Flight Human-System Standard Volume 1, Revision A: Crew Health.</i> Retrieved from https://standards.nasa.gov/standard/nasa/nasa-std-3001-vol-1</ref>.
 
Nevertheless, there are defined legal limits for exposure during work for several professional activities, such as for X-ray assistants, airplane personnel, etc. The International Commission on Radiation Protection recommends that occupational (work-related) radiation exposure be limited to 50 millisieverts (mSv) per year, and limited to 100 mSv over any 5-year period<ref>http://www.icrp.org/publication.asp?id=ICRP%20Publication%20103</ref>. NASA's radiation dose limits for astronauts are established in NASA-STD-3001<ref>NASA. (2015). <i>NASA Space Flight Human-System Standard Volume 1, Revision A: Crew Health.</i> Retrieved from https://standards.nasa.gov/standard/nasa/nasa-std-3001-vol-1</ref>.
  
The equivalent dose rate from cosmic radiation on Earth's surface at sea level is 0.26 mSv per year<ref name=":3">http://www.ans.org/pi/resources/dosechart/msv.php</ref>.  Based on measurements made by the Curiosity rover, the corresponding figure for the surface of Mars is approximately 230 mSv/year<ref name=":0">http://science.sciencemag.org/content/343/6169/1244797.full</ref>.  Curiosity also measured the temporary increase in radiation during a single SPE.  The results indicate an increase in equivalent dose rate of approximately 25% over a 1-day interval<ref name=":0" />.  This figure will vary depending on the intensity of a particular SPE.
+
There is scientific uncertainty surrounding the health hazard from cosmic and solar radiation, because most past research on the health effects of radiation studied only x-rays and gamma rays<ref name=":1" />. 
 +
 
 +
===Limits for plants===
 +
 
 +
==Martian Environment==
 +
 
 +
=== Effects of the Martian atmosphere ===
 +
Most SPE particles will be stopped by the atmosphere before they reach the surface.  However, interactions with atmospheric particles can produce neutrons; those neutrons can reach the surface, so the health hazard is not eliminated.
 +
 
 +
Cosmic radiation protons are likely to penetrate the atmosphere.  Cosmic ray heavy ions may fragment in the atmosphere, producing lower-mass ions that can still harm astronauts on the surface.<ref name=":4">Beaty DW, Snook K, Carlton A, Eppler D, Farrell B, Heldmann J,...Zeitlin C, on behalf of the Mars Human Precursor Science Steering Group. (2005). An Analysis of the Precursor Measurements of Mars Needed to Reduce the Risk of the First Human Mission to Mars. Available at <nowiki>https://mepag.jpl.nasa.gov/reports/MHP_SSG_(06-02-05).pdf</nowiki></ref>
 +
 
 +
=== Effects of regolith ===
 +
When cosmic radiation strikes regolith, it can cause the impacted atoms to emit their own radiation.  Surrounding regolith particles absorb much of this radiation, with the exception of neutrons.  
 +
 
 +
Neutrons generated in this way are called albedo neutrons.  These neutrons have the potential to add substantially to the radiation dose for astronauts on the surface.<ref name=":4" />
 +
 
 +
=== Dose received by an unprotected human on Mars ===
 +
 
 +
==== Cosmic radiation ====
 +
The equivalent dose rate from cosmic radiation on Earth's surface at sea level is 0.26 mSv per year<ref name=":3" />.  Based on measurements made by the Curiosity rover, the corresponding figure for the surface of Mars is approximately 230 mSv/year<ref name=":0">Hassler DM, Zeitlin C, Wimmer-Schweingruber RF, Ehresmann B, Rafkin S, Eigenbrode JL,...MSL Science Team. (2014). Mars' Surface Radiation Environment Measured with the Mars Science Laboratory's Curiosity Rover. Science 343(6169). <nowiki>https://doi.org/10.1126/science.1244797</nowiki></ref>.  More generally, one model estimated that the dose equivalent rate on the surface of Mars ranges from 156.4 mSv/year (at solar maximum) to 273.8 mSv/year (at solar minimum)<ref name=":2" /><ref>McKenna-Lawlor S, Goncalves P, Keating A, Reitz G, Matthia D. (2012). Overview of Energetic Particle Hazards During Prospective Manned Missions to Mars. Planetary and Space Science. 63: 123-132.</ref>.  A 2005 report by the Mars Human Precursor Science Steering Group estimated that (at solar minimum) the dose from cosmic radiation would be 1.2 +/- 0.5 mSv/day; this includes 0.4 +/- 0.4 mSv/day from albedo neutrons.<ref name=":4" />  
  
There is scientific uncertainty surrounding the health hazard from cosmic and solar radiation, because most past research on the health effects of radiation studied only x-rays and gamma rays<ref name=":1" />.   
+
==== Solar Proton Events ====
 +
Curiosity also measured the temporary increase in radiation during a single SPE.  The results indicate an increase in equivalent dose rate of approximately 25% over a 1-day interval<ref name=":0" />.  This figure will vary depending on the intensity of a particular SPE.
  
 
==Effect on material==
 
==Effect on material==
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"In this work, it is shown that on the Martian surface, almost any amount of aluminum shielding increases exposure levels for humans. The increased exposure levels are attributed to neutron production in the shield and Martian regolith as well as the electromagnetic cascade induced in the Martian atmosphere. This result is significant for optimization of vehicle and shield designs intended for the surface of Mars."  <ref name=":2">NASA, Tony C. Slaba, Christopher J. Mertens, and Steve R. Blattnig '' Radiation Shielding Optimization on Mars '', https://spaceradiation.larc.nasa.gov/nasapapers/NASA-TP-2013-217983.pdf, Apr 2013.</ref>
 
"In this work, it is shown that on the Martian surface, almost any amount of aluminum shielding increases exposure levels for humans. The increased exposure levels are attributed to neutron production in the shield and Martian regolith as well as the electromagnetic cascade induced in the Martian atmosphere. This result is significant for optimization of vehicle and shield designs intended for the surface of Mars."  <ref name=":2">NASA, Tony C. Slaba, Christopher J. Mertens, and Steve R. Blattnig '' Radiation Shielding Optimization on Mars '', https://spaceradiation.larc.nasa.gov/nasapapers/NASA-TP-2013-217983.pdf, Apr 2013.</ref>
  
"An in-situ shielding strategy will also be of little help unless several hundred g/cm2 of regolith is utilized. Such a strategy would probably require large scale excavation making it an unlikely candidate. Instead, the shielding strategy would rely primarily on material optimization. Options, such as replacing aluminum structures with high hydrogen content carbon composites, could be pursued." <ref name=":2" />  This opinion is open to argument as in-situ resources utilization for any type of settlement should make large amounts of regolith available for construction.  It mainly is true for the very first level of habitats
+
"An in-situ shielding strategy will also be of little help unless several hundred g/cm2 of regolith is utilized. Such a strategy would probably require large scale excavation making it an unlikely candidate. Instead, the shielding strategy would rely primarily on material optimization. Options, such as replacing aluminum structures with high hydrogen content carbon composites, could be pursued." <ref name=":2" />  This opinion is open to argument as in-situ resources utilization for any type of settlement should make large amounts of regolith available for construction.  It mainly is true for the very first level of habitats.
 
 
The use of g/cm2 can be translated into an equivalent thickness that depends on the material density. For martian regolith at 2000 kg/m3, a thickness of 1m of regolith is 200 g/cm2.  Water (or ice) is 100 g/cm2. 
 
 
 
==Open issues==
 
  
*What is the required thickness of a [[water]] layer upon a house for radiation shielding?
+
The use of g/cm2 can be translated into an equivalent thickness that depends on the material density.  For martian regolith at 2000 kg/m3, a thickness of 1m of regolith is 200 g/cm2.  Water (or ice) is 100 g/cm2.  So the minimum covering for a long term settlement would be 5m or more.  For water, although the radiation absorption is better the density is lower, so about the same thickness would be required for protection <sup>(to be discussed)</sup>
  
 
==References==
 
==References==

Latest revision as of 11:02, 13 October 2019

Nuclear Danger Icon

Natural Radiation on Mars is much higher compared with Earth. The thin atmosphere provides only a small shielding effect against harmful solar radiation and cosmic radiation. Mars also lacks the magnetosphere that protects Earth.

The average natural radiation level on Mars is 24-30 rads or 240-300 mSv per year(needs checking and reference). This is about 40-50 times the average on Earth.

Occasional solar flares produce particularly high doses. Some Solar Proton Events (SPEs) were observed by MARIE that were not seen by sensors near Earth due to the fact that SPEs are directional. Astronauts on Mars could be warned of SPEs by sensors closer to the Sun and presumably take shelter during these events. This would imply an Early Warning System (possibly a network of sensors in orbit around the sun or a single sensor in Lagrangian point L1) might be needed to ensure all SPEs threatening Mars were detected early enough.

1 millisievert [mSv] = 0.1 rad [rd]

Types of Radiation

Radiation comes in a variety of forms:[1]

Name Relative Biological
Effectiveness (RBE)
Source
X-Rays and Gamma Rays 1 Radiation belts, solar radiation, and bremsstrahlung electrons
Electrons

1.0 MeV
0.1 MeV


1
1.08

Radiation belts
Protons

100 MeV
1.5 MeV
0.1 MeV


1-2
8.5
10

Cosmic radiation, inner-radiation belts, and solar radiation
Neutrons

0.05 ev (thermal)
1.0 MeV
10 MeV


2.8
10.5
6.4

Nuclear interactions in the sun; on Mars, produced when cosmic radiation interacts with regolith
Alpha Particles

5.0 MeV
1.0 MeV


15
20

Cosmic radiation
Heavy Ions Varies widely Cosmic radiation

(RBE is a measure of the damage done to living tissue, relative to gamma rays)

Cosmic radiation comprises 85% protons, 14% alpha particles, and 1% heavy ions.[2]  Solar radiation includes the same radiation types, but it a higher proportion of protons and its heavy primaries have lower energy levels.  The high-energy heavy primaries in cosmic radiation can penetrate materials that effectively block lower-energy radiation[3].

Exposure limits

Limits for humans

Exposure to dangerous levels of radiation causes radiation sickness and cancer. Any exposure to radiation, no matter how slight, poses some risk. Small dose - small risk of cancer. High dose - high risk of cancer. The average exposure to radiation on Earth due to natural sources is 6.2 mSv per year[4]

Nevertheless, there are defined legal limits for exposure during work for several professional activities, such as for X-ray assistants, airplane personnel, etc. The International Commission on Radiation Protection recommends that occupational (work-related) radiation exposure be limited to 50 millisieverts (mSv) per year, and limited to 100 mSv over any 5-year period[5]. NASA's radiation dose limits for astronauts are established in NASA-STD-3001[6].

There is scientific uncertainty surrounding the health hazard from cosmic and solar radiation, because most past research on the health effects of radiation studied only x-rays and gamma rays[3]

Limits for plants

Martian Environment

Effects of the Martian atmosphere

Most SPE particles will be stopped by the atmosphere before they reach the surface.  However, interactions with atmospheric particles can produce neutrons; those neutrons can reach the surface, so the health hazard is not eliminated.

Cosmic radiation protons are likely to penetrate the atmosphere.  Cosmic ray heavy ions may fragment in the atmosphere, producing lower-mass ions that can still harm astronauts on the surface.[7]

Effects of regolith

When cosmic radiation strikes regolith, it can cause the impacted atoms to emit their own radiation.  Surrounding regolith particles absorb much of this radiation, with the exception of neutrons.  

Neutrons generated in this way are called albedo neutrons.  These neutrons have the potential to add substantially to the radiation dose for astronauts on the surface.[7]

Dose received by an unprotected human on Mars

Cosmic radiation

The equivalent dose rate from cosmic radiation on Earth's surface at sea level is 0.26 mSv per year[4]. Based on measurements made by the Curiosity rover, the corresponding figure for the surface of Mars is approximately 230 mSv/year[8]. More generally, one model estimated that the dose equivalent rate on the surface of Mars ranges from 156.4 mSv/year (at solar maximum) to 273.8 mSv/year (at solar minimum)[9][10]. A 2005 report by the Mars Human Precursor Science Steering Group estimated that (at solar minimum) the dose from cosmic radiation would be 1.2 +/- 0.5 mSv/day; this includes 0.4 +/- 0.4 mSv/day from albedo neutrons.[7]

Solar Proton Events

Curiosity also measured the temporary increase in radiation during a single SPE.  The results indicate an increase in equivalent dose rate of approximately 25% over a 1-day interval[8].  This figure will vary depending on the intensity of a particular SPE.

Effect on material

Radiation can change the properties of plastics and metals, making them brittle after a period of time.

Protection

Habitats should be equipped with a radiation shielding, thick enough to reduce the radiation to a level equal to Earth, that is, almost zero. Best protection may be achieved with houses built in natural caves or set into cliffs or hillsides.

Space suits must be designed with radiation in mind. The suit should provide adequate shielding for the occupant. It may be necessary to design suits with several grades of protection. Suits designed for short-term use can carry lighter shielding which would reduce weight and improve maneuverability.

During severe radiation events, such as solar flares, surface settlements may use storm shelters with heavier than normal shielding.

"In this work, it is shown that on the Martian surface, almost any amount of aluminum shielding increases exposure levels for humans. The increased exposure levels are attributed to neutron production in the shield and Martian regolith as well as the electromagnetic cascade induced in the Martian atmosphere. This result is significant for optimization of vehicle and shield designs intended for the surface of Mars." [9]

"An in-situ shielding strategy will also be of little help unless several hundred g/cm2 of regolith is utilized. Such a strategy would probably require large scale excavation making it an unlikely candidate. Instead, the shielding strategy would rely primarily on material optimization. Options, such as replacing aluminum structures with high hydrogen content carbon composites, could be pursued." [9] This opinion is open to argument as in-situ resources utilization for any type of settlement should make large amounts of regolith available for construction. It mainly is true for the very first level of habitats.

The use of g/cm2 can be translated into an equivalent thickness that depends on the material density. For martian regolith at 2000 kg/m3, a thickness of 1m of regolith is 200 g/cm2. Water (or ice) is 100 g/cm2. So the minimum covering for a long term settlement would be 5m or more. For water, although the radiation absorption is better the density is lower, so about the same thickness would be required for protection (to be discussed)

References

  1. http://www.nas.nasa.gov/About/Education/SpaceSettlement/designer/needs.html#SHIELDING
  2. Schimmerling W. (2011, Feb 5). The Space Radiation Environment: An Introduction. https://three.jsc.nasa.gov/concepts/SpaceRadiationEnviron.pdf
  3. 3.0 3.1 Rapp D. (2006). Radiation Effects and Shielding Requirements in Human Missions to the Moon and Mars. Mars 2:46-71. https://doi.org/10.1555/mars.2006.0004
  4. 4.0 4.1 http://www.ans.org/pi/resources/dosechart/msv.php
  5. http://www.icrp.org/publication.asp?id=ICRP%20Publication%20103
  6. NASA. (2015). NASA Space Flight Human-System Standard Volume 1, Revision A: Crew Health. Retrieved from https://standards.nasa.gov/standard/nasa/nasa-std-3001-vol-1
  7. 7.0 7.1 7.2 Beaty DW, Snook K, Carlton A, Eppler D, Farrell B, Heldmann J,...Zeitlin C, on behalf of the Mars Human Precursor Science Steering Group. (2005). An Analysis of the Precursor Measurements of Mars Needed to Reduce the Risk of the First Human Mission to Mars. Available at https://mepag.jpl.nasa.gov/reports/MHP_SSG_(06-02-05).pdf
  8. 8.0 8.1 Hassler DM, Zeitlin C, Wimmer-Schweingruber RF, Ehresmann B, Rafkin S, Eigenbrode JL,...MSL Science Team. (2014). Mars' Surface Radiation Environment Measured with the Mars Science Laboratory's Curiosity Rover. Science 343(6169). https://doi.org/10.1126/science.1244797
  9. 9.0 9.1 9.2 NASA, Tony C. Slaba, Christopher J. Mertens, and Steve R. Blattnig Radiation Shielding Optimization on Mars , https://spaceradiation.larc.nasa.gov/nasapapers/NASA-TP-2013-217983.pdf, Apr 2013.
  10. McKenna-Lawlor S, Goncalves P, Keating A, Reitz G, Matthia D. (2012). Overview of Energetic Particle Hazards During Prospective Manned Missions to Mars. Planetary and Space Science. 63: 123-132.

External links