Difference between revisions of "Radiation"

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==Open issues==
 
==Open issues==
*What is the required thickness of a [[regolith]] or [[water]] layer upon a house for radiation shielding?
+
*What is the required thickness of a [[water]] layer upon a house for radiation shielding?
 
*Does regolith emit an own portion of radiation, some kind of secondary radiation due to the long exposure to cosmic and solar radiation?
 
*Does regolith emit an own portion of radiation, some kind of secondary radiation due to the long exposure to cosmic and solar radiation?
  

Revision as of 11:12, 12 February 2018

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.

Occasional solar flares produce particular 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.

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 rays, inner-radiation belts, and solar cosmic rays
Neutrons

0.05 ev (thermal)
1.0 MeV
10 MeV


2.8
10.5
6.4

Nuclear interactions in the sun
Alpha Particles

5.0 MeV
1.0 MeV
Heavy Primaries


15
20
varies widely

Cosmic rays

Danger

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.

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[2]. NASA's radiation dose limits for astronauts are established in NASA-STD-3001[3].

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[5]. 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[5].  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

Houses 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.

Open issues

  • What is the required thickness of a water layer upon a house for radiation shielding?
  • Does regolith emit an own portion of radiation, some kind of secondary radiation due to the long exposure to cosmic and solar radiation?

References

External links