Radiation sickness

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

Measuring radiation

There are several different ways of measuring radiation described below. We will use the Sievert (Sv) in this article.

Measurements independent of biological damage

• One decay per second is 1 Becquerel (Bq). This is a TINY measure of radiation, so small that it is not much use in the real world, but scientists might use it when measuring very, very small radiation levels.
• A Curie (Ci) is defined as 37 billion Becquerel. This is a dangerous amount of radiation, and if you are near something this radioactive, you would want to leave soon.
• The Roentgen (R) measures how much ionization is in the air. (This is a pretty indirect way to measure radiation, but it does has the advantage that it measures Ionizing Radiation which is what is dangerous to us.) 1 R is about 0.01 Sv. (1 Sv is getting to the "getting dangerous" range, so it would take 100 hours of 1 R / hour exposure to reach this level.) Whereas, 1 R per second is a "get out of there right now!" level of radiation.

Radiation comes in various types, and Bq just counts 'particles'. So a particle with very low energy (which is not dangerous) counts the same as high energy particles.

Radiation weighting factors

When thinking about radiation doses that could effect humans, weighting factors can be applied to various types of radiation, with gamma rays being given a weight on 1, and other types being measured relative to gamma rays.

These weighting factors are multiplied by the energy of the particle. So note that while all electromagnetic radiation has a Weighting factor of '1', gamma rays carry more energy, so they are more dangerous than X-rays. Likewise, a high energy alpha particle is more dangerous than a low energy one, even tho both have the same Weighting factor.

Radiation Weighting Factors

Type of Radiation	Weighting Factor	Notes
Photons (all energies)	1	Note that higher frequency photons carry more energy
Electrons & muons (all energies)	1
Protons & charged pions	2
Alpha particles, fission fragments & heavy ions	20
Neutrons	~10	A continuous function based on neutron energy

Figure 1: Neutron Weighting Factor to Energy in Mega electron Volts log scale

(For the neutron function, see Figure 1, or Equation 4.3, on page 66 of the English version of the 2007 Recommendations of the International Commission on Radiological Protection, ICRP Publication 103, published in 2007.)

Basically neutrons have a weighting factor of about 2.5 for both low and high energies. For a fairly broad range of energies, the weighting factor ranges from 2.5 to 13. Then for a narrow spike around 1 MeV, the weighting factor ranges from about 13 to 20.5.

Some people approximate this by saying the weighting factor is around 10, but as can be seen, this is an oversimplification. See the figure to the right.

Radiation measurements weighing biological damage

The following radiation measurements have weightings to show how dangerous they are to living tissue.

• The REM (Roentgen Equivalent Man) is an older measurement of radiation. It has to be multiplied by a weighting factor depending on the type of radiation.
• The RAD (Radiation Absorbed Dose) is like the REM, but with the various weighting factors already cooked in. One RAD is equal to 100 ergs of energy absorbed per gram of material (tissue). 100 RAD is 1 Gy or 1 Sv.
• A Gray (Gy) is a slightly out of date measure of radiation. It has been replaced with the Sievert, but basically one Gray = 1 Sievert.
• A Sievert (Sv) is the system international measure of radiation. It is basically the Gray, but with slightly more accurate weighting factors. To a non-specialist, the two measurements are identical. We will use the Sievert from this point forward.

Lethal doses of radiation

If you get a large dose of radiation is a short period of time, then the numbers below should give you a good idea if the dose is survivable.

• Radiation doses of 2 to 3 Sv might cause death (especially if the patient is already unhealthy), by weakening the immune system and eventually resulting in a fatal infection. With good medical treatment, this dose is usually survivable.
• Radiation doses of 4 Sv are usually lethal, if untreated. With good medical treatment this dose is often survivable.
• Doses of 6 Sv may be survivable with hospital care.
• Doses of 8 Sv are lethal unless exotic treatment is started (e.g. bone marrow transplant, with extreme precautions to prevent infection).
• A dose of 10 Sv or more has 100% lethality.

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), alpha particles, or rarely other atomic nuclei (often iron). 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 are killed. The organism gets sick, its immune system is depressed, and it 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. Death will happen within minutes or an hour or two.

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 radar) 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 affected

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 cause 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.)

• 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.

Long term effects

If you survive severe radiation poisoning, the heavy metabolic burden will have aged the body. These commonly include: cancer, cardiovascular disease, frailty, sarcopenia, and mild cognitive impairment.

-- Discussion: I (Rick) remember seeing somewhere that 1 Sv of radiation ages you about 2 years, but I can't find a good reference. This is likely a huge oversimplification.--

Treatment

The first thing to do is to decontaminate the outside of the body. Remove radioactive clothing, wash off dust, etc. This is very important and should be done as quickly as possible.

Then remove any radioactive material from inside the body. Inducing coughing to expel fallout, surgically remove any radioactive masses, etc.

People with radiation poisoning often become immune impaired. Keep them clean, in as close to sterile environments as possible to reduce the chance of infection.

Then treat the symptoms. If the patient has diarrhea, give them water, or saline injections to hydrate them. Normal procedures may be used to treat: bacterial infections, headache, fever, diarrhea, nausea & vomiting, dehydration, burns, sores, or ulcers.

Specific treatments

• Potassium iodide will cause iodine to be absorbed by the thyroid, preventing radioactive iodine from being absorbed. This must be done within 1 day of exposure.
• Prussian blue (a dye) will bind to radioactive caesium and thallium, removing them from the body more quickly. This is a form of chelation therapy (which uses chemicals to pull heavy metals out of the body).
• Diethylenetriamine pentaacetic acid (DTPA). Another chelation therapy which binds to plutonium, americium, and curium (and other metals).

(Note that virtually ALL heavy metals are toxic to some degree or another. This is in addition to any radiation danger.)

See this reference: , for more information.

Note that the above treatments are aimed more at people who have absorbed fallout, rather than getting radiation from solar storms. For body wide doses from a solar storm supportive treatment is likely the best that can be done. However, the following treatments may be of use:

• Granulocyte colony-stimulating factor, filgrastim (Neupogen), sargrmostime (Leukine), and pegfilgrastim (Neulasta), may increase white blood cell production.
• Transfusions of red blood cells or blood platelets.

Protection

There are three basic ways to protect yourself from radiation:

• Be far from a radiation source. For example, if there is a local radiation source, by doubling the distance from it, you quarter the dose. (This does not much help from a solar flare of course.)
• Minimize the duration of your exposure. As quickly as possible get to a well shielded location.
• Maximize Radiation shielding. Mars settlements are likely to have a Storm shelter with very high radiation protection. During high radiation events, go inside this volume and stay there until the solar storm is over. (Typically 2 to 5 hours.)

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
• Electromagnetic radiation
• Ionizing Radiation
• Radiation shielding
• Solar Wind
• Cosmic radiation

References

Henderson TO, Ness KK, Cohen HJ. Accelerated aging among cancer survivors: from pediatrics to geriatrics. Am Soc Clin Oncol Educ Book. 2014:e423–30. 10.14694/EdBook_AM.2014.34.e423