GLOSSARY OF SELECTED TERMS IN NUCLEAR SCIENCE 



439 



proportional region : The range of operating voltage for a counter tvibe or ionization 

 chamber in which the gas aniplitication is greater than 1 and is independent of the pri- 

 mary ionization. In this region the pulse size is proportional to the number of ions 

 produced as a result of the initial ionizing event. 



proton • \ positivelv charged elementary particle of mass number 1 and charge eciual 

 in magnitude to the electronic charge r. It is one of the constituents of every nucleus. 

 The number of protons in the nucleus of each atom of an ehMuent is given by th(> atomic 



number Z of the element. , r 



pulse-height discriminator: A circuit designed to select and pass voltage pulses ot a 



certain minimum amplitude. 



quality • \ term for the approximate characterization of radiation with regard to 

 its penetrating power. It is usually expressed in terms of effective wavelength or 



half-value. ,.,,., • i. 



quenching : The process of inhibiting continuous or multiple discharges m a counter 



tube that uses gas amplification. 



radiation: The emission and propagation of energy through space or through a 

 material medium in the form of waves; for instance, the emission and propagation of 

 electromagnetic waves or of sound and elastic waves. 



radiation chemistry: The branch of chemistry that is concerned with the chemical 

 effects (including decomposition) of high-energy radiation and particles on matter. 



radiation counter tube : A radiation detector capable of providing discrete electrical 

 pulses in response to the incidence of radiation. 



radio- : A prefix denoting radioactivity or relationship to it. 



radioactive : (a) Exhibiting radioactivity. (5) Pertaining to radioactivity. 



radioactive equilibrium : A condition that may obtain in the course of the decay of 

 a radioactive parent having shorter-lived descendants, in which the ratio of the activ- 

 ity of the parent to that of a descendant is independent of time. This condition can 

 exist only when no activity longer-lived than that of the parent is interposed in the 



decay chain. . j- j.- „ 



radioactive half -life : The time in which the amount of a particular radioactive 



isotope is reduced to half its initial value. 



radioactive tracer: Small quantity of radioactive isotope, either with carrier or 

 carrier-free, used to follow biological, chemical, or other processes. Since the stable 

 and radioactive isotopes of an element have essentially the same chemical properties 

 and the radioactive ones are readily detected, the movement and behavior of the stable 

 atoms can be traced by following the radioactivity. In this case the compound under 

 observation is said to be labeled with the radioactive isotope. 



radioactivity : (a) The phenomenon of spontaneous transformation, with a measura- 

 ble lifetime, of a nuclide. See decay, radioactive, (b) A term designating a partic- 

 ular spontaneously disintegrating nuclide, (c) A term for the intensity ot emission 

 from a sample undergoing spontaneous nuclear disintegration, (d) A term designating 

 a particular component of radiation from a sample undergoing spontaneous nuclear 



'^''raSbiology: That branch of biology which deals with the effects of radiation on 



liiological systems. „ ■, , 



radiocolloid : A clumping of radioactive atoms into colloidal aggregates. 

 radioelement : (a) An element with no stable isotopes, (b) An element tagged with 



a radioactive isotope. , , 



radioisotope : (a) Any radioactive isotope of an element, {b) A word loosely used 



as a synonym for radionuclide. , j., ■ ■ ■ 



radiology : The medical science of radioactive substances, X rays, and other ionizing 



