How Radiation Sickness Works

When radiation of high enough energy strikes anatomin the human body, it can strip away an electron. The resulting positively charged atom is called an ion, which explains why high energy radiation is called ionizing radiation. The release of the electron produces 33 electron volts (eV) of energy, which heats the surrounding tissues and disrupts certain chemical bonds. Extremely high-energy radiation can even destroy the nuclei of atoms, releasing even more energy and causing more damage. Radiation sickness is the cumulative effect of all this damage on a human body that's been bombarded with radiation.

Ionizing radiation comes in three flavors: alpha particles, beta particles and gamma rays. Alpha particles are the least dangerous in terms of external exposure. Each particle contains a pair of neutrons and a pair of protons. They don't penetrate very deeply into the skin, if at all — in fact, clothing can stop alpha particles. Unfortunately, alpha particles can be inhaled or ingested, usually in the form of radon gas. Once ingested, alpha particles can be very dangerous. However, even then they don't typically cause radiation sickness — instead, they lead to lung cancer.

Beta particles are electrons that move very quickly — that is, with a lot of energy. Beta particles travel several feet when emitted from a radioactive source, but they're blocked by most solid objects. Beta particles are about 8,000 times smaller than alpha particles — and that's what makes them more dangerous. Their small size allows them to penetrate clothing and skin. External exposure can cause burns and tissue damage, along with other symptoms of radiation sickness. If radioactive material enters food or water supplies or is dispersed into the air, people can inhale or ingest beta particle emitters unknowingly. Internal exposure to beta particles causes much more severe symptoms than external exposure.

Gamma rays are the most dangerous form of ionizing radiation. These extremely high energy photons can travel through most forms of matter because they have no mass. It takes several inches of lead — or several feet of concrete — to effectively block gamma rays. If you're exposed to gamma rays, they pass through your entire body, affecting all of your tissues from your skin to the marrow of your bones. This causes widespread, systemic damage.

How much radiation does it take to cause radiation sickness, and what effect does this damage have on a human body? That's next. For more detailed information on different types of radiation and where they come from, take a look at How Radiation Works.

When we talk about the amount of radiation needed to trigger a certain set of radiation sickness symptoms, we're not talking in terms of absolute amounts. Instead, we're talking about the total dosage. This dosage takes a number of factors into account, including the intensity of the radiation, how much is absorbed by a typical human body, how long the body is exposed to the source, and what types of radiation are involved. The unit of measure that accounts for all of these factors is the sievert (Sv), which measures absorption of radioactive energy multiplied by a quality factor that changes depending on whether the radiation being measured is alpha particles, beta particles or gamma rays.

A burst dose of 0.75 Sv can be enough to induce radiation sickness, including nausea and a weakened immune system. Three sieverts will cause more severe effects but usually won't be fatal if you receive medical care. An instantaneous dose of 10 or more sieverts will be fatal, even with medical care. A dose somewhere in between gives you a roughly 50 percent chance of dying within 30 days. Remember that we're referring to an instantaneous, acute dose — if the same dose is spread out over a longer period of time, the effects will be reduced.

That might seem a little scary since it takes less than a single sievert to make you sick. For comparison, if you go to the hospital and get a CT scan, you'll receive slightly over 0.01 Sv of radiation. If you're a worker in a radiation-heavy environment, federal guidelines limit the maximum yearly dose to 0.05 Sv. According to the EPA, the average person receives around .0062 Sv each year, around half of which is from natural background radiation.

So, what does radiation sickness actually look like? Radiation sickness initially manifests with symptoms within a few minutes or hours of exposure; these symptoms include nausea, diarrhea, headache, fever and even, in severe cases, loss of consciousness. High doses also cause burns on the skin. Symptoms occur more quickly the greater the dose of radiation and will fade in one or two days. Following that is a latent period, a lull during which there are no symptoms. The latent period lasts several weeks, although the larger the dose, the shorter the latent period — and with exposures above roughly 10 Sv, there is no latent period.

Unfortunately, after the latent period, the real damage becomes evident. The radiation damages cells and structures within the body. Most vulnerable is bone marrow, where stem cells produce blood cells. Damaged marrow can't produce enough red or white blood cells, leaving the body anemic and susceptible to infections. Radiation also damages the cells that line the digestive system, not only preventing that system from functioning properly but allowing bacteria to migrate from the digestive tract into the blood, causing more infections.

What happens when an intense burst of radiation causes severe radiation sickness? We'll talk about that in the next section.

What we know about severe radiation sickness comes from a relatively small number of accidents involving radioactive materials, as well as the victims of the Hiroshima and Nagasaki atomic bomb attacks.

At 5 Sv and up, radiation can damage skin so severely that it doesn't heal properly. Hair falls out. Scars develop beneath the skin will that swell and form keloids. Unfortunately, some scientists know the horrors of radiation exposure firsthand. For instance, physicist Harry K. Daghlian, Jr. suffered a 5.1 Sv exposure in 1945 while working on a plutonium core. He suffered severe burns to his hands and died 25 days after the accident. Another physicist, Louis Slotin, suffered a similar accident — using the exact same core — just one year later. Slotin was exposed to a 21 Sv dose, which is a massive amount of radiation. He vomited immediately, and then suffered through nine days of horrific symptoms before dying. The incident that killed Slotin was so intense that the air in the lab itself became ionized, causing a clear blue glow and a visible wave of heat. His symptoms were very similar to those seen in victims of the atomic bomb attacks on the Japanese cities of Hiroshima and Nagasaki.

Once you're exposed, how are you treated? Radiation sickness treatment starts with decontaminating the patient if any radioactive material is still present. External decontamination involves washing, while internal exposure (from inhalation or ingestion) requires the use of special drugs, such as Prussian blue dye or diethylenetriaminepentaacetic acid (DTPA), which binds to radioactive particles and flushes them from the body. Symptoms can be treated individually to ease the patient's suffering. Antibiotics are used to fight or prevent infections since the immune system is so weakened by bone marrow damage. If the marrow is only slightly damaged, blood transfusions can increase the chance of survival. If damage is severe, a bone marrow transplant may offer some hope.

The best way to prevent radiation sickness, of course, is to avoid intense sources of radiation. The most common way for people to become exposed to a radioactive source is by encountering improperly disposed of radioactive materials that were used in industry or medicine. For example, in 1987, scavengers found a radiation source used for radiation therapy in an abandoned hospital in Goiânia, Brazil. Finding the glowing blue caesium inside decorative, the scavengers sold it, exposing dozens of people to gamma radiation. Four people eventually died of radiation sickness.