Federal Emergency Management Agency (FEMA) Standardized Awareness Practice Test

What is radiation defined as?

1. Energy emitted by stable atoms

2. Invisible energy emitted by certain types of unstable atoms

3. Energy that can only travel downstream

4. Visible light emitted by radioactive materials

The correct answer is: Invisible energy emitted by certain types of unstable atoms

Radiation is fundamentally defined as the energy emitted by certain types of unstable atoms, which are often referred to as radioactive. These unstable atoms undergo a process known as radioactive decay, during which they release energy in the form of particles or electromagnetic waves. This energy can be invisible, such as gamma rays or X-rays, or may manifest as alpha or beta particles. The definition accurately captures the essence of radiation, specifically focusing on the characteristics of unstable atoms, which distinguishes it from mere energy emitted by stable atoms or forms of energy that are visible, such as light. Furthermore, the concept of energy traveling solely downstream is not applicable to radiation, since it can propagate in various directions and through different mediums without being confined to a single flow direction. Hence, the definition provided is specific and encapsulates the nature of radiation as it pertains to the behavior of unstable atoms.