BACKGROUND RADIATION	The radiation in man's natural environment consisting of cosmic rays and radiation from naturally radioactive elements as well as from building materials.
BARRIERS	Barriers of radiation absorbing material such as lead and concrete used to reduce radiation exposure.
BECQUEREL	The System International (SI) unit for radioactivity in which the number of disintegrations is equal to one disintegration per second (dps).
BETA PARTICLE	Charged particle emitted from the nucleus of an atom during radioactive decay. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron.
BIOLOGICAL HALF-LIFE	HALF-LIFEThe time required for a biological system to eliminate by natural processes half the amount of a substance, such as radioactive material, that has entered it.
BIOASSAY	The determination of kinds, quantities or concentrations, and in some cases, the locations of radioactive material in the human body, whether by direct measurement (in-vivo counting) or by analysis and evaluation of materials excreted or removed from the human body.
BODY BURDEN	The amount of radioactive material, which if deposited in the toal body, will produce the maximum permissible dose rate to the critical organ.
BONE SEEKER	A radioisotope that tends to accumulate in the bones when introduced into the body.
BREMS-STRAHLUNG	Electromagnetic ( X-ray ) radiation produced by the deposition of charged particles in matter. Secondary photon radiation produced by the decleration of charged particles through matter. Usually associated with energetic beta emitters such as Phosphorous-32.