Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Radiation flux is a measure of the flow of radiation from a given radioactive source. Radiation flux density is a related measure that adds area dimensions to the above definition - for example, radiation-flux/square-centimeter. Particle radiation is the radiation of energy by means of fast-moving subatomic particles. Particle radiation is referred to as a particle beam if the particles are all moving in the same direction, similar to a light beam. Due to the wave-particle duality, all moving particles also have wave character. Higher energy particles more easily exhibit particle characteristics, while lower energy particles more easily exhibit wave characteristics.