Chapter 9 Physical Science (What Is Radioactivity)

Alpha Particle

A positively charged atom that is released in the disintegration of radioactive elements and that consists of two protons and two neutrons.

Radioactive Tracer

A radioactive material that is added to a substance so that its distribution can be detected later.

Beta Particle

A charged electron emitted during certain types of radioactive decay, such as beta decay.

Nuclear Chain Reaction

A continuous series of nuclear fission reactions.

Gamma Ray

The high-energy photon emitted by a nucleus during fission and radioactive decay.

Critical Mass

The minimum mass of of a fissionable isotope that provides the number of neutrons needed to sustain a chain reaction.

Background Radiation

The nuclear radiation that arises naturally from cosmic rays and from radioactive isotopes in the soil and air.

Nuclear Radiation

The particles that are released from the nucleus during radioactive decay.

Fission

The process by which a nucleus splits into two more fragments and releases neutrons and energy.

Radioactivity

The process by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation.

Fusion

The process in which light nuclei combine at high temperatures, forming heavier nuclei and releasing energy.

Rem

The quantity of ionizing radiation that does as much damage to human tissue as 1 roentgen of high-voltage X rays does.

Half-Life

The time required for half of a sample of a radioactive substance to disintegrate by radioactive decay or by natural process.