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Radiation Safety

Background Information
Gamma Radiation
Health Concerns

Radiation Theory
Nature of Radiation
Sources of High Energy

Rad for Ind Radiography
Decay and Half-life
Energy, Activity, Intensity   and Exposure
Interaction with Matter
Measures Related to   Biological Effects

Biological Effects
Biological Factors
Stochastic (Delayed) Effects
  -Genetic Effects

Nonstochastic (Acute) Effects

Safe Use of Radiation
NRC & Code of Federal
Exposure Limits
Controlling Exposure
  -Time-Dose Calculation
  -Distance-Intensity Calc
HVL Shielding
Safety Controls

Survey Techniques

Radiation Safety Equipment
Radiation Detectors
Survey Meters
Pocket Dosimeter
Audible Alarm Rate Meters
Film Badges

Video Clips



Radioactive Decay and Half-Life

As mentioned previously, radioactive decay is the disintegration of an unstable atom with an accompanying emission of radiation. As a radioisotope atom decays to a more stable atom, it emits radiation only once. To change from an unstable atom to a completely stable atom may require several disintegration steps and radiation will be given off at each step. However, once the atom reaches a stable configuration, no more radiation is given off. For this reason, radioactive sources become weaker with time. As more and more unstable atoms become stable atoms, less radiation is produced and eventually the material will become non-radioactive.

The decay of radioactive elements occurs at a fixed rate. The half-life of a radioisotope is the time required for one half of the amount of unstable material to degrade into a more stable material. For example, a source will have an intensity of 100% when new. At one half-life, its intensity will be cut to 50% of the original intensity. At two half-lives, it will have an intensity of 25% of a new source. After ten half-lives, less than one-thousandth of the original activity will remain. Although the half-life pattern is the same for every radioisotope, the length of a half-life is different. For example, Co-60 has a half-life of about 5 years while Ir-192 has a half-life of about 74 days.