A positively charged particle made up of two neutrons and two protons emitted by certain radioactive nuclei. Alpha particles can be stopped by a few inches of air or thin layers of light materials, such as a sheet of paper, and pose no direct or external radiation threat; however, they can pose a serious health threat if ingested or inhaled. More information.


An electron or positron emitted by certain radioactive nuclei. Beta particles can be stopped by aluminum. They can pose a serious direct or external radiation threat and can be lethal depending on the amount received. They also pose a serious internal radiation threat if inhaled or ingested. More information.


To build up in the food chain.  For example mice pick up a certain toxin from contaminated grass.  A hawk consumes ten mice, the hawk will accumulate the toxins from all mice.


Capable of causing cancer.


A pure substance consisting of atoms or ions from at least two different elements. The compound usually has characteristics unlike the elements that make it up. Example, two hydrogen atoms and one oxygen atom make a compound we call H2O, or water.


A measure of radioactivity based on the observed decay rate of approximately one gram of radium. The Curie was named in honor of Pierre and Marie Curie, pioneers in the study of radiation. One curie of radioactive material will have 37 billion atomic transformations (disintegrations) in one second. More information.


The splitting of a nucleus into at least two other nuclei and the release of a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation. Fissioning is also referred to as 'burning.' Fissioning that occurs without any outside cause, such as bombardment with a neutron, is called 'spontaneous fission.'


High-energy electromagnetic radiation emitted by certain radionuclide"s when their nuclei transition from a higher to a lower energy state. These rays have high energy and a short wave length. All gamma rays emitted from a given isotope have the same energy, a characteristic that enables scientists to identify which gamma emitters are present in a sample. Gamma rays are very similar to x-rays. More information.


The time in which one half of the atoms of a radioactive isotope disintegrates into another nuclear form. Half-lives vary from billionths of a billionth of a second to billions of years. Also called physical or radiological half-life. biological half-life - the time an organism takes to eliminate one half the amount of a compound or chemical on a strictly biological basis effective half life - incorporates both the radioactive and biological half-lives. It is used in calculating the dose received from an internal radiation source. More information.


Exposed to radiation


A nuclide of an element having the same number of protons but a different number of neutrons. More information.

Maximum contaminant level (MCL)

The amount of a contaminant that may be present in drinking water under the Safe Drinking Water Act. MCLs are the standards that drinking water treatment systems must meet.


One-thousandth of a rem, or a Roentgen Equivalent Man (rem). It’s a unit of equivalent dose. Rem relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose.


A general term applicable to all atomic forms of an element. Nuclides are characterized by the number of protons and neutrons in the nucleus, as well as by the amount of energy contained within the atom. More information.


A small particle, typically found within an atom's nucleus, that possesses a positive electrical charge. The number of protons is unique for each chemical element.


Energy given off as either particles or rays from the unstable nucleus of an atom. Why are some atoms radioactive? Can unstable atoms become stable?


An unstable form of a nuclide. More information.


The degree or extent to which something is toxic (harmful, poisonous, deadly).