Definitions and Units of Measure

DOE-HDBK-1130-98

Radioactive material is any material containing unstable atoms that emit radiation.

Radioactivity

Radioactivity is the process of unstable (or radioactive) atoms becoming stable. This is done

by emitting radiation. This process over a period of time is referred to as radioactive decay.

A disintegration is a single atom undergoing radioactive decay.

Radioactivity units

Radioactivity is measured in the number of disintegrations radioactive material undergoes in a

certain period of time.

a. Disintegrations per minute (dpm)

b. Disintegrations per second (dps)

c. Curie (Ci)

One curie equals:

2,200,000,000,000 disintegrations per minute (2.2x1012 dpm), or

37,000,000,000 disintegrations per second (3.7x1010 dps), or

1,000,000 microcuries (1x106 Ci).

Radioactive half-life

Radioactive half-life is the time it takes for one half of the radioactive atoms present to

decay.

Radioactive contamination

Radioactive contamination is radioactive material that is uncontained and in an unwanted

place. (There are certain places where radioactive material is intended to be.)

Contamination is measured per unit area or volume.

dpm/100 cm2

Ci/ml

Ci/g.

Ionization

Ionization is the process of removing electrons from neutral atoms.

Electrons will be removed from an atom if enough energy is supplied. The remaining

atom has a positive (+) charge. The ionized atoms may affect chemical processes in

cells. The ionizations may affect the cell's ability to function normally.

The positively charged atom and the negatively charged electron are called an "ion pair."