Radiation Fundamentals

What is Radiation?

Radiation is in every part of our lives. It occurs naturally in the earth and can reach us through cosmic rays from outer space. Radiation may also occur naturally in the water we drink or the soils in our backyard. It even exists in food, building materials, and in our own human bodies.

Radiation is used for scientific purposes, medical reasons, and to power some submarines. We can also come into contact with radiation through sources such as X-rays, nuclear power plants, and smoke detectors.

What are some of the terms associated with radiation?

Radiation can be defined as energy given off by the nucleus of an atom in the form of particles or rays.

Radiation is the same whether it happens in atoms that are made by nature or in atoms that scientists make.

The atom is the smallest unit that shows the chemical behavior characteristics of an element. The center of each atom has a nucleus that contains protons and neutrons.

• Protons are positively charged particles.

• Neutrons, which have no electrical charge, hold the protons together.

• Electrons are negatively charged particles. The electrons surround the nucleus and travel in orbits.

There is a theory called The Rutherford-Bohr Theory of atomic structure. It compares the atom to our solar system. At the center of every atom is the positively charged nucleus, which could be compared to the sun in our solar system. The electrons move around the nucleus as if in orbit. Just like the earth orbits around the sun. Repelling forces exist between the nuclear particles. Any change in the number, position, or energy of the nucleons can upset their balance. If this happens, the nucleus becomes unstable or radioactive.

There are different types of radiation; some are more energetic than others. For example, non-ionizing radiation has enough energy to move atoms around, but not enough to change them chemically. The most energetic form of radiation is called ionizing radiation.

 Back to Top

How do you measure radiation?

Since small amounts of material contain very large numbers of atoms, small samples can have a very large number of atoms disintegrating at the same time. It didn't take radiation scientists very long to decide that working with activities in the billions of disintegrations per second was too awkward. To make measuring activity more convenient, they developed a new unit, the curie, named in honor of Marie Curie, a pioneer in the study of radioactive materials.

Radiation Measurements  

The International System of Units has been given official status and recommended for universal use by the General Conference on Weights and Measures.

 Back to Top

What does the term "half-life mean?

The term half-life is defined as the time it takes for one-half of the atoms of a radioactive material to disintegrate. After one half-life the level of radioactivity of a substance is halved, after two half-lives it is reduced to one quarter, after three half-lives to one-eighth and so on.

The Half-Life for Some Naturally Occurring Radioisotopes

The Half-Life for Some Man-Made Radioisotopes Used in Medicine

Back to Top

Radiation and the Human Body

Scientists estimate that the average person in the United States receives a dose of about 360 millirem of radiation per year. But what are the sources of that exposure: where does it come from?

Eighty percent of human exposure comes from natural sources: radon gas, the human body, outer space, and rocks and soil. The remaining twenty percent comes from man-made radiation sources, primarily medical X-rays.

How does one protect oneself from radiation?

There are three concepts in basic radiation protection. They are: Time, Distance, & Shielding

Time

If you decrease the amount of time you spend near the source of radiation, you decrease the amount of radiation exposure you receive. To imagine this, think of a trip to the beach as a comparison. If you spend a lot of time on the beach, you will be exposed to the sun, and, ultimately, get a sunburn. If you spend less time in the sun and more time in the shade, your sunburn will be much less severe. This is similar to the way radiation exposure works.

Distance

The farther away you are from a radiation source, the less exposure you will receive. Compare this to an outdoor concert. You can sit directly in front of a speaker or 50 yards from the stage oron the grass in the park across the street. If you sit in front of the speaker, you will probably suffer some damage to your hearing. If you sit 50 yards from the stage, you will be exposed to an average amount of music. If you sit in the park across the street, the noise is even further reduced and you might not even hear the concert, or even know what song they are playing.

Radiation exposure is similar. The closer you are to the source, the greater your chances for developing some damage to your body. If you are far from the source, your exposure would be much lower.

Shielding

If you increase the shielding around a radiation source, it will decrease your exposure. For example, if you stand out in the rain without an umbrella, you will get wet. But, if you use an umbrella to shield you from the rain, you will remain dry and protected. This is similar to the idea of shielding in radiation protection.

What are the types of radiation?

There are three main types of ionizing radiation: alpha, beta, gamma. They may be found in sources of man-made radiation as well as natural radiation sources.

 Characteristics of Ionizing Radiation 

Back to Top

What are the biological effects resulting from exposure to radiation?

Cells are undamaged by the dose.

Ionization may form chemically active substances which in some cases alter the structure of the cells. These alterations may be the same as those changes that occur naturally in the cell and may have no negative effect.

Cells are damaged, repair the damage and operate normally

Some ionizing events produce substances not normally found in the cell. Cells can repair the damage if it is limited. Many thousands of chromosome aberrations (changes) occur constantly in our bodies. We have effective mechanisms to repair these changes.

Cells are damaged, repair the damage and operate abnormally

If a damaged cell needs to perform a function before it has had time to repair itself, it will either be unable to perform the repair function or perform the function incorrectly or incompletely. Such cells can be the underlying causes of cancers.

Cells die as a result of the damage

If a cell is extensively damaged by radiation, or damaged in such a way that reproduction is affected, the cell may die. Radiation damage to cells may depend on how sensitive the cells are to radiation.

All cells are not equally sensitive to radiation damage. In general, cells which divide rapidly and/or are relatively non-specialized tend to show effects at lower doses of radiation then those which are less rapidly dividing and more specialized. Examples of the more sensitive cells are those which produce blood. This system (called the hemopoietic system) is the most sensitive biological indicator of radiation exposure.

Back to Top

What are theSources of Radiation at the WSSRAP?

The following naturally occurring radioactive materials are present in the cell:

How much radiation am I receiving at the WSSRAP from these sources?

Walking to the top of the disposal cell and standing on the platform at the peak you will receive less exposure to radiation than you would receive standing in your own backyard. The cover of the disposal cell consists of multiple layers, including the clay radon barrier, geosynthetic liners, sand, and crushed limestone rock surface layers. By its nature such crushed rock emits lower background radiation levels than soil. The combination of reduced radon emissions and lower background emissions from the crushed limestone rock result in lower overall radiation emissions on the cell surface than the average levels in clean soil in the St. Louis Area.

How much radiation am I receiving from other sources?  

What was the highest external dose received by a worker at the WSSRAP?

The WSSRAP has had only a few worker radiation doses above 100 mrem/year, the highest of which was a total effective radiation dose of 192 mrem/year in 1996 during Raffinate Pit 4 debris consolidation.

Portions of information for this display were obtained from www.epa.gov/radiation.

Back to Top

To Subsurface Investigations

Back to Interpretive Center Online Tour