GLOSSARY OF SELECTED TERMS IN NUCLEAR SCIENCE 429 



Increase of atoniic muiiber occurs with negative l)eta-i>article emission, decrease with 

 positive beta-particle (positron) emission or upon electron capture. 



beta particle: A negative electron or a positive electron (|)()sit ron i cinillcil from a 

 nucleus (hu'ing lieta decay. The fi, /:f~, and /:J+ are reserved for electrons of mich^ar 

 origin. 



beta ray: A synonym for beta particle. 



billion electron volts: A unit of energy, symbol Bev, equal to 10^ ev. 



binary scaler: .\ scaler wliose scaling factor is 2. 



biologic half-life (of a radioactive substance) : The time in which a living tissue, 

 organ, or individual eliminates, through biologic processes, one-half of a given amount 

 of a substance that has been introduced into it. 



biophysics: The study of phenomena of living organisms by physical methods; the 

 study of physical phenomena exhibited by living organisms or parts thereof. 



bone marrow : Soft tissue that fills the cavity in most bones; one of the most impor- 

 tant sites of formation of blood constituents. 



bone seeker: Any compound or ion that migrates in vivo preferentially into bone. 



bound water: In the drying of solids, water that is chemically combined. 



break-through : That point in an adsorption cycle at which the effluent begins to 

 show a marked increase in concentration of the substance being adsorbed. 



bremsstrahlung : Secondary photon radiation produced by deceleration of charged 

 particles passing through matter. 



cancer: Any malignant neoplasm. 



carrier : (a) A quantity of an element which may be mixed with radioactive isotopes 

 of that element, giving a ponderable quantity to facilitate chemical operations. (6) 

 .\ substance in ponderable amount which, when associated with a trace of another 

 substance, will carry the trace with it through a chemical or physical process, especially 

 a precipitation process. If the added substance is a different element from the trace, 

 the carrier is called a nonisotopic carrier. 



carrier-free : Designating a preparation of a radioactive isotope which for practical 

 purposes is essentially free of stable isotopes of the element in question. 



characteristic radiation : Radiation originating from an atom following the removal 

 of an electron. The wavelength of the emitted radiation depends only on the element 

 concerned and the particular energy levels involved. 



chemical exchange : A process in which isotopes of the same element in two difYerent 

 molecules exchange places. 



chronic exposure : Term used to denote radiation exposure of long duration liy frac- 

 tionation or protraction. 



cloud chamber, or expansion chamber : A device for observing the paths of ionizing 

 particles, based on the principle that supersaturated vapor condenses more readily on 

 ions than on neutral molecules. 



coincidence : The occurrence of counts in two or more detectors simultaneously or 

 within an assignable time interval, ideally as a result of the passage of a single particle 

 or of several generically related particles. 



coincidence circuit: An electronic circuit that produces a usable output pulse only 

 when each of two or more input circuits receives pulses simultaneously or within an 

 assignable time interval. 



coincidence loss, coincidence correction: See dead-time correction. 



condenser r-meter : \n instrument consisting of an air-wall ionization chamber 

 together with auxiliary equipment for charging and measuring its voltage, used as an 

 integrating instrument for measuring the (juantity of X or gamma radiation in roent- 

 gens. See ionization chamber. 



