|MadSci Network: Physics|
Here is one reference to hopefully answer your question: The Earth, and all living things on it, are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from protons to iron nuclei derived from the sun and from other sources outside our solar system. This radiation interacts with atoms in the atmosphere to create secondary radiation, including X- rays, muons, protons, alpha particles, pions, electrons, and neutrons. The immediate dose from cosmic radiation is largely from muons, neutrons, and electrons, and this dose varies in different parts of the world based largely on the geomagnetic field and altitude. This radiation is much more intense in the upper troposphere, c. 10km altitude, and is thus of particular concern for airline crews and frequent passengers, who spend many hours per year in this environment. Here, the radiation exposure is not primarily due to the cosmic ray interaction with the thin atmosphere, but with the dense fuselage of the aircraft, causing relatively high background radiation in the cabin while the aircraft is at high altitude. Similarly, cosmic ray interaction with spacecraft components produces secondary radiation that causes higher background exposure in astronauts than in humans on the surface of Earth. Astronauts in low orbits, such as in the International Space Station or the Space Shuttle, are at low risk because the magnetic field of the Earth shields out most cosmic rays. Outside low Earth orbit, as experienced by the Apollo astronauts who travelled to the moon, this background radiation is much more intense, and represents a considerable obstactle to potential future long term human exploration of the moon or Mars. Cosmic rays also cause elemental transmutation in the atmosphere, in which secondary radiation generated by the cosmic rays combine with atomic nuclei in the atmosphere to generate different radioactive isotopes. Many so-called cosmogenic nuclides can be produced, but probably the most notable is carbon-14, which is produced by interactions with nitrogen atoms. These cosmogenic nuclides eventually reach the earth's surface and can be incorporated into living organisms. The production of these nuclides varies slightly with short-term variations in solar cosmic ray flux, but is considered practically constant over long scales of thousands to millions of years. The constant production, incorporation into organisms and relatively short half-life of carbon-14 are the principles used in radiocarbon dating of ancient biological materials such as wooden artifacts or human remains. Another reference writes.... Cosmic rays may prevent long-haul space travel The radiation encountered on a journey to Mars and back could well kill space travellers, experts have warned. Astronauts would be bombarded by so much cosmic radiation that one in 10 of them could die from cancer. The crew of any mission to Mars would also suffer increased risks of eye cataracts, loss of fertility and genetic defects in their children, according to a study by the US Federal Aviation Administration (FAA). Cosmic rays, which come from outer space and solar flares, are now regarded as a potential limiting factor for space travel. "I do not see how the problem of this hostile radiation environment can be easily overcome in the future," says Keran O'Brien, a space physicist from Northern Arizona University, US. "A massive spacecraft built on the moon might possibly be constructed so that the shielding would reduce the radiation hazard," he told New Scientist. But even so he reckons that humans will be unable to travel more than 75 million kilometres (47 million miles) on a space mission – about half the distance from the Earth to the Sun. This allowance might get them to Mars or Venus, but not to Jupiter or Saturn. Risky business Helped by O'Brien, the FAA's Civil Aerospace Medical Institute in Oklahoma City investigated the radiation doses likely to be received by people on a 2.7-year return trip to Mars, including a stay of more than a year on the planet. The study estimated that individual doses would end up being very high, at 2.26 sieverts. This is enough to give 10% of men and 17% of women aged between 25 and 34 lethal cancers later in their lives, it concludes. The risks are much higher than the 3% maximum recommended for astronauts throughout their careers by the US National Council on Radiation Protection and Measurements. The risks are smaller for older people because cancers have less time to develop. But women are always in more danger than men because they live longer and are more susceptible to breast and ovarian cancers. The study warns that cosmic rays would also increase the risk of cataracts clouding the eyes. Furthermore, men exposed to a solar flare might suffer a temporary reduction in fertility, and the chances that any children conceived by travellers to Mars will have genetic defects are put at around 1%. Serious brain damage The study's lead author, the FAA's Wallace Friedberg, highlights other work suggesting that heavy nuclei in cosmic radiation cause "serious brain damage" in mice, leading to memory loss. "Heavy nuclei exposure must be a serious consideration for space missions such as a trip to Mars," he says. Improving spaceships' shielding by using water, hydrogen or plastics can protect astronauts to some extent. But this is limited by the constrictions of craft weight and design, Friedberg points out. "Increased speed would also reduce radiation exposure" by reducing journey times, he notes. "And drugs or food supplements that can reverse radiation damage are being considered." Others suggest more radical solutions might be needed. "Radiation exposure is certainly one of the major problems facing future interplanetary space travellers," says Murdoch Baxter, founding editor of the Journal of Environmental Radioactivity. "Unless we can develop instantaneous time and space transfer technologies like Dr Who’s TARDIS." Journal reference: Radioactivity in the Environment (vol 7, p 894) Another reference is: http://www.sirr.unina.it/Asi/collegamenti/Introduction/introduction.ht ml
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