Chapter 9 - Nuclear Changes
Alpha particle – Is a positively charged atom that is released in the disintegration of
radioactive elements and that consists of two protons and two neutrons
Background Radiation – The nuclear radiation that arises naturally from cosmic rays and
from radioactive isotopes in the soil and air.
Beta particle – A charged electron emitted during certain types of radioactive decay, such
as beta decay.
Critical Mass – The minimum mass of a fissionable isotope that provides the number of
neutrons needed to sustain a chain reaction.
Fission – The process by which a nucleus splits into two or more fragments and releases
neutrons and energy.
Fusion – The process in which light nuclei combine at extremely high temperatures.
Forming heavier nuclei and releasing energy
Gamma Ray – the high-energy photon emitted by a nucleus during fission and
radioactive decay
Hal-life the time required for half of a sample of a radioactive substance to disintegrate
by radioactive decay or by natural processes.
Nuclear Chain Reaction – A continuous series of nuclear fission reactions.
Nuclear Radiation – The particles that are released from the nucleus during radioactive
decay.
Radioactivity – The process by which an unstable nucleus emits one or more particles or
energy in the form of electromagnetic radiation
Radioactive tracer – A radioactive material that is added to a substance so that its
distribution can be detected later.
Rem – The quantity of ionizing radiation that does as much damage to human tissue as I
roentgen of high-voltage x rays does.