Radioactive materials give off a form of energy that travels in waves or particles. This energy is called radiation. When a person is exposed to radiation, the energy penetrates the body. For example, when a person has an x-ray, he or she is exposed to radiation.
Radiation is measured using the unit sievert or rem, which quantifies the amount of radiation absorbed by human tissues. One sievert is 1,000 millisieverts (mSv). One millisievert is 1,000 microsieverts. One sievert can be converted to 100 rem.
People are constantly exposed to low levels of naturally occurring radiation called background radiation and man-made sources. Background radiation comes from cosmic radiation and from radioactive elements in air, water, and earth. Cosmic radiation is concentrated at the poles by the earth’s magnetic field and attenuated by the atmosphere. Thus, exposure is greater for people living at high latitudes, at high altitudes, or both and during airplane flights. Radioactive elements, particularly uranium, are present in many rocks and minerals. These elements end up in various substances, including food, water, and construction materials. The doses from natural background radiation are far too low to cause radiation injuries, although they may increase the risk of cancer. Man-made sources involve medical imaging and radiation therapy.
- Normally, people are exposed to natural radiation of 2-3 mSv a year. In some parts of the world, people receive between 5 and 10 mSv a year.
- In a CT scan, the organ being studied typically receives a radiation dose of 15 mSv in an adult to 30 mSv in a newborn infant.
- A typical chest X-ray involves exposure of about 0.02- 0.67 mSv, while a dental x-ray can be 0.01 mSv.
What happens after radiation exposure?
Radiation can affect the body in a number of ways, and the adverse health effects of exposure may not be apparent for many years. These adverse health effects can range from mild effects, such as skin reddening, to serious effects such as cancer and death, depending on the amount of radiation absorbed by the body (the dose), the type of radiation, the route of exposure, and the length of time a person was exposed.
Exposure to 100 mSv a year is the lowest level at which any increase in cancer risk is clearly evident. A cumulative 1,000 mSv (1 sievert) would probably cause a fatal cancer many years later in five out of every 100 persons exposed to it.
Large doses of radiation or acute radiation exposure destroys the central nervous system, red and white blood cells, which compromises the immune system, leaving the victim unable to fight off infections.
For example, a single one sievert (1,000 mSv) dose causes radiation sickness such as nausea, vomiting, bleeding, but not death. A single dose of 5 sieverts would kill about half of those exposed to it within a month.
Though rare, but radiation accidents happens, here are some examples.
- The Japanese Government reports at one point, radiation levels near the stricken plant on the northeast coast reached as high as 400 millisieverts (mSv) an hour. That would be would be 20 times the annual exposure for some nuclear-industry employees and uranium miners. Radiation levels then dropped to about 0.6 millisieverts per hour.
- Exposure to 350 mSv was the criterion for relocating people after the Chernobyl accident, according to the World Nuclear Association.
If radioactive iodine is released into the air after a radiological or nuclear event it can be breathed into the lungs. In most cases, once radioactive iodine has entered the body, the thyroid gland quickly absorbs it. After it has been absorbed into the thyroid gland, radioactive iodine can then cause thyroid gland injury. Potassium iodide, also called KI, is a prophylaxis to block radioactive iodine rom being taken into the thyroid gland and protect this gland from injury.
The thyroid gland cannot tell the difference between stable and radioactive iodine and will absorb both. KI works by blocking radioactive iodine from entering the thyroid. When a person takes KI, the stable iodine in the medicine gets absorbed by the thyroid. There is so much stable iodine in the KI that the thyroid gland becomes “full” and cannot absorb any more iodine—either stable or radioactive—for the next 24 hours.
It is also important to know what KI cannot do. KI cannot protect parts of the body other than the thyroid from radioactive iodine. KI cannot protect the body from any radioactive elements other than iodine. If radioactive iodine is not present, then taking KI is not protective.
It is important to know that KI may not give a person 100% protection against radioactive iodine. How well KI blocks radioactive iodine depends on:
- How much time passes between contamination with radioactive iodine and taking KI (the sooner a person takes KI after being exposed to radioactive iodine, the better),
- How fast KI is absorbed into the blood, and
- The total amount of radioactive iodine to which a person is exposed.
A single dose of KI protects the thyroid gland for 24 hours. Taking a higher dose of KI, or taking KI more often than recommended, does not offer more protection and can cause severe illness or death.
- CDC (www.cdc.gov)