GLOSSARY OF SELECTED TERMS IN NUCLEAR SCIENCE 441 



secondary radiation: lladiation originating as the result of absorption of other 

 r-HU'itiou in nrittrr It uiay be either electromagnetic or particulate in nature. 

 ^ selective localization (isotopes): In the use of radioisotopes, accumulation of a 

 particular isotopc> to a significantly greater degree in certain cells or tissues, bee 



differential absorption ratio. , 1.1, ** 



self -absorption : Absorption of radiation emitted by radioactive atoms by the matter 

 in which the atoms are located; in particular, the absorption of radiation from a sam- 

 nle being assayed in the sample itself. , j u , 



self-quenched counter tube: A Geiger-MiiUer counter tube that is quenched by 

 means of a suitable component in the counting gas. , ^ , , . ,, , 



self-scattering: The scattering of radioactive radiations by the body of the sub- 

 stance emitting the radiation. Self-scattering may outweigh self-absorption and may 

 increase the measured activity over that expected for a weightless sample. 



sensitive volume: That portion of a counter tube or ionization chamber winch 



'T:^::S:^'i::^re^or, ,n radiobiolo.y): Part of a cell particularly 



''^::::^^^ ^::^:rX amount of radiation reaching one region of 



anaop from another region of space. . 



"^ specific acUvity, gram element: Total radioactivity of a given isotope per gram of 



'''Secific activity, isotope: Total radioactivity of a given isotope per gram of the 



't^^:^^^^^^^^ Number of ion pairs per unit length of path of the ionization 

 particle in a medium, e.g., per centimeter of air or per micron of tissue. 



spurious counts : Counts caused by imperfections of the counter. 



sfable: (a) Exhibiting no tendency to undergo any spontaneous nuclear leaction 

 not observably radioactive, (b) Exhibiting no tendency to undergo a Particular 

 spontaneous nuclear reaction; thus, e.g., beta stable, stable with respect to beta decay^ 



surdng voltage: For a counter tube, the minimum voltage that must be applied 

 to obtain counts with the particular circuit with which ,t is associated. 



staStlal error (counting) : Errors in counting due to the random tune distributions 



°' ^:!^l Radiation not serving any useful purpose. It includes direct radia- 

 tion and secondary radiation from irradiated objects. 



suvey instrument: A portable instrument used for detecting and measuring radia- 

 tion under various physLl conditions. The term covers a wide range of devices 

 utilizing most of the detection methods defined elsewhere. 



survfval curve: (a) Curve obtained by plotting the number or percentage of organ- 

 isin rv v"g at a given time against the dose of radiation. (6) Curve showing the 

 pZenTage of'indivfduals surviving at different intervals after a particular dose of 



^^ civndrome • The complex of symptoms associated with any disease . 



Lied^tom :The atomic position in a molecule which is distingu.shcd by ,.otop,c 



tracer 



tagged atoms: Atoms of an isotopic tracer. , , , .■ i„, +^ r^rnHnee 



tafget : The material subjected to bombardment by accelerated particles to produce 

 electromagnetic radiation or nuclear reactions within the materia ^t^". 



target theory (hit theory) : Theory explaining some biologic ^f ^^s oj radiatuni onj^he 

 basis of ionization occurring in a very small ^f^^'^^.1^^^^7;^^^^ 

 or more "hits," i.e., ionizing events within the sensitive volume, may be necessary 



bring about the effect. 



