Radiation sickness

Acute radiation sickness in Mars settlements may result from prolonged exposure to solar radiation or accidental exposure to radioactive materials.

Sources of radiation

Solar radiation

• Settlers on the surface of Mars, with no protection (only a light weight space suit protecting them from the tenuous and cold Mars atmosphere) may receive leathal doses of solar radiation during solar storms.
• Astronauts in Mars orbit will also be unprotected (unlike Earth orbit, where low orbits are protected by the Earth's magnetic field), so some spacewalk tasks should be carried out by robots whenever possible and sufficient protection must be provided when a solar storm is imminent. People in transit to Mars, or in Mars orbit, would go into a Storm shelter if there is an active solar storm.

Galactic cosmic rays

Galactic cosmic rays (GCR) are a form of damaging radiation that require shielding for protection against long term exposure. GCRs are mostly protons (hydrogen with no electron) or other atomic nuclei. They move at very high velocities, and the fastest ones have much more kinetic energy than even the highest energy photons. They therefore do proportionally more damage than other types of radiation and are difficult to protect against. On Earth, the depth and density of the atmosphere block most cosmic rays. But on Mars the atmosphere is not dense enough and additional protection is required.

See Cosmic radiation for more information.

Accidental exposure to radioactive material

• Should nuclear power be required by an expanding settlement, accidental exposure to radioactive material may result in injury or death. Long-term health problems (such as cancer) may result from being in close proximity to such materials.

Low Level Radiation Exposure

Life is constantly bombarded with low level radiation, from cosmic rays and natural radioactivity in the environment. The body takes low levels of damage from this and constantly repairs this damage.

At very low levels, there is significant evidence that radiation is healthy. See Radiation Hormesis for more details.

At higher levels of radiation, cells take internal damage, and may even die. This has an overall aging effect on the organism, with a higher incidence of cancer later in life being the best documented aging effect. A key concept is the rate of the damage. If the damage is repaired as fast, or faster than the body takes this damage, it has little long term effect. Thus a sudden burst of radiation all at once is considerably more dangerous than a larger dose spread over a long period.

At high levels of radiation exposure, cells are damaged, and many die. The organism gets sick, their immune system is depressed, and they may die. This is known as Acute Radiation Syndrome, Radiation Sickness, or Radiation Poisoning, and is discussed below.

At very high radiation doses, it effects the nervous system and may cause seizures and immediate death.

Acute Radiation Syndrome

Radiation sickness is caused by ionizing radiation passing thru the body, and by high energy Electromagnetic radiation such as x-rays and gamma rays, which are absorbed by atoms in the body which then knock off electrons (which are ionizing radiation). Non-ionizing radiation (such as neutrinos, microwaves, or mesons) do no harm to the body.

Ionizing radiation is simply charged particles moving thru the body. A high energy charged particle knocks electrons off of atoms (forming free radicals), which can damage the structure of RNA, DNA, proteins, and enzymes. If a cell takes enough of this damage it can stop supporting nearby cells, die, or become cancerous.

Radiation sickness, is simply when many cells die in the body, caused by a sudden burst of radiation. Symptoms can start within hours for high doses, to days, or a week or two. Symptoms can last for weeks or months, and even after recovery, tend to have an aging effect on an organism.

The initial symptoms are usually nausea, loss of appetite, and vomiting. Initial symptoms may improve, then later symptoms may take effect.

Cells most effected

Damage to cells can slow or prevent cell division even if the cell is not killed outright. Thus cells that reproduce the most quickly in the body cause the first signs of sickness. These include the gastrointestinal (gut) cells, and the cells involved in the immune system. Damage to the bone marrow (another type of fast reproducing cell) can lower red cell blood counts.

Notes on other cells types

Slow growing and reproducing cells can take the time to repair damage without causing problems outside themselves. Muscle cells are an example of this type.

The skin reproduces fairly quickly, and enough damage to the skin can cause burns, which allow easier access of pathogens to the body. The flash of a nuclear explosion may cause widespread skin burns from the heat flash, tho this is not the ionizing radiation damage being discussed here.

Damage to the bone marrow can reduce white blood cell counts, which makes the organism more vulnerable to infection.

Cells in the lung are not unusually vunerable to radiation, but if radioactive particles are breathed in, they may nestle in the lung tissue for a time causing local burns. Also, damage to the lungs is dangerous in its own right, as damaged tissue can cause fluid to leak into the air sacks, causing infection or death.

Main types of damage

There are 3 main types of radiation sickness:

• Hematopoietic: This is damage to the blood cells. A drop in red blood cells slows the flow of oxygen to cells, which have an increased metabolic burden, as they try to repair damage. Drops in white blood cells make infections more likely. A drop in platelets slows healing of bleeding (and the gut may well be bleeding from radiation damage). Doses of 0.25 Sievert (Sv) = 25 Rad may causes clinically detectable decrease in blood production, but patients may not notice symptoms until the dose reaches 1.0 Sievert.

• Gastronintestinal: The damage to the gut causes nausea, vomiting, loss of appetite, and abdominal pain (caused by internal bleeding). Death usually follows from infection, rather than direct damage to the gut. These symptoms typically occur at 4 Sv or higher. (6 Sv for quick onset.) Radiation doses above 4 Sv are usually lethal, unless exotic treatment is started (e.g. bone marrow transplant, with extreme precautions to prevent infection).

• Neurovascular: These symptoms usually occur at doses over 30 Sv, tho less severe effects may happen with doses as low as 10 Sv. The patient experiences dizziness, headache, and decreased levels of consciousness. This happens within minutes to hours, and is fatal, even with aggressive intensive care.

See this wikipedia article for further information.

Symptoms and treatment

Acute radiation syndrome is the result of Ionisation damage from intense radiation

Cancer is a longer term result from radiation exposure

Nerve damage

Cooking of tissue

Genetic damage

Protection

Radiation shielding

Exposition limits are used to define what can be acceptable as far as radiation dosages go. As the body can self repair up to a point, some radiation is acceptable. Rather like sunscreen, that protects against low power radiation from the sun, so sunbathers can stay out longer.

See Also

• Radiation
• Solar Wind