438 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



nucleonics: Nuclear technology; the applications of nuclear science in physics 

 astronomy, chemistry, biology, geology, industry, and armaments, and the techniques 

 associated with these applications. 



nucleus : The positively charged core of an atom, with which is associated practically 

 the whole mass of the atom but only a minute part of its volume 



nucleus (of a cell): A definitely delineated body within a cell, containing the 

 chromosomes. 



nuclide : A species of atom characterized by the charge, mass number, and quantum 

 state of Its nucleus. In order to be regarded as a distinct nuclide, the species must be 

 capable of existing for a measurable lifetime (generally greater than lO^-i" sec) Thus 

 nuclear isomers are separate nuclides, but promptly decaying excited nuclear states 

 and unstable intermediates in nuclear reactions are not so considered. 



osseous: Bony. 



osteogenic : Derived from or composed of tissue concerned in the growth or reoair 

 of bone. 



parent, parent nuclide: A nuclide that undergoes decay into another nuclide the 

 daughter; a radioactive precursor. ' 



percentage depth dose : Amount of radiation delivered at a specified depth in tissue 

 expressed as a percentage of the amount delivered at the skin. 



periosteum: The tough fibrous membrane surrounding bone; a place of frequent 

 radiation injury. 



permissible dose : The amount of radiation that may be received bv an individual 

 within a specified period with the expectation of no harmful result to himself For 

 long-continued X- or gamma-ray exposure of the whole body, it is 0.3 r/week measured 



in air. 



phantom (radiology) : A volume of material behaving in essentially the same manner 

 as tissue, with respect to the radiation in question, which is used to simulate a portion 

 of the human body and into which ionization chambers can be placed. Measurements 

 made in a phantom permit the determination of the radiation dose delivered to the 

 skin and points within the body. Materials commonly used for X rays are water 

 Masonite Presdwood (unit density), and beeswax. 



pile : A nuclear reactor. The term pile comes from the first nuclear reactor which 

 was made by piling up graphite blocks and pieces of uranium and uranium oxide. The 

 term reactor is becoming more commonly used. 



plateau characteristic, counting rate-voltage characteristic: The relation between 

 counting rate and voltage applied to a counter tube for a given constant source of 

 radiation. 



platelet (thrombocyte) : A small colorless corpuscle present in large numbers in the 

 blood of all mammals, believed to play a role in the clotting of blood. 



pocket chamber: A small pocket-sized ionization chamber used for monitoring the 

 radiation exposure of personnel. Before use it is given a charge, and the amount of 

 discharge is a measure of the quantity of radiation received. 



pocket meter: A complete pocket-sized radiation instrument by means of which a 

 quantity of radiation can be directly indicated. 



polycythemia: A disease characterized by overproduction of ervthrocytes 



positron : A positive electron. Positrons are formed in the process of pair produc- 

 tion, in the beta decay of many radionuclides, and in some more specialized processes 



proportional counter: An instrument comprising a proportional counter tube with 

 its associated circuits. Often loosely applied to the proportional counter tube itself 



proportional counter tube : A radiation counter tube or chamber operated in the 

 proportional region. 



