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Answer to Question #1549 Submitted to "Ask the Experts"Category: Environmental and Background Radiation — Space Flight The following question was answered by an expert in the appropriate field: Q
What are the radiation levels on the moon and Mars? A
The radiation levels on the moon and Mars are similar and change with the approximate 11-year variation in the solar cycle. At present we are near the maximum solar activity part of the cycle. Radiation levels on Mars are probably lower than on the moon's surface because Mars has a thin atmosphere, composed mainly of carbon dioxide, that acts as a radiation shield. Estimates of radiation levels in deep space for thinly shielded spacecraft resulting from galactic cosmic rays range from ~ 0.3 Sv per year during solar maximum activity (about now) to ~ 1 Sv per year during solar minimum periods (L.W. Townsend, F.A. Cucinotta, and J.W. Wilson, "Interplanetary Crew Exposure Estimates for Galactic Cosmic Rays," Radiation Research 129:48-52; 1992). On a planetary surface the mass of the planet provides shielding from about half of the cosmic rays, resulting in estimated exposures that are about half of those given above. Solar particle events (sometimes called flares, which is not correct terminology) result from eruptions on the sun and can provide very high levels of radiation exposure (up to several Gy from energetic protons) unless adequate shielding (10-20 cm thickness of water or equivalent) is available for protection. A recent study of radiation levels and dose rates for a very large solar particle event is found in J.L. Parsons and L.W. Townsend, "Interplanetary Crew Dose Rates for the August 1972 Solar Particle Event," Radiation Research 153:729-733; 2000. Larry Townsend, PhD Editor's Note: Viewers of this answer have asked a question about the numbers given by Dr. Townsend for galactic cosmic ray (GCR) doses. It appears that there is an error in the answer. However, Dr. Townsend states: "There is no error. The maximum GCR fluxes occur during periods of minimum solar activity ('solar minimum') and vice versa. The GCR particles enter the solar system from out in the galaxy. Particles with lower energies are deflected by the magnetic fields in the plasma carried away from the sun by the solar wind. Hence, maximum solar activity means maximum plasma (with entrained magnetic fields) which means that lower energy GCR particles are deflected before they reach the inner solar system which means that we are at a GCR minimum which means smaller doses (and vice versa)."
Answer posted on 1 February 2002. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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