436 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



labile : A synonym for unstable. 



latent period (radiology) : Interval between irradiation and appearance of the effect 

 in question. 



latent tissue injury (radiology) : Injury which does not become manifest until some 

 time after irradiation, and possibly until some other trauma has supervened. This 

 second injury may be so slight that it would not, of itself, produce observable damage. 



Lauritsen electroscope : A rugged yet sensitive electroscope employing a metalized 

 quartz fiber as the sensitive element. 



LD50 dose : See median lethal dose. 



LD50 time : See median lethal time. 



lead equivalent : The thickness of lead affording the same reduction in radiation dose 

 rate under specified conditions as the material in question. 



length of plateau : The voltage interval corresponding to the portion of the plateau 

 characteristic in which a Geiger-Miiller counter tube can be reliably operated. See 

 plateau characteristic. 



leukemia : .\ disease in which there is often great overproduction of white blood 

 cells, or relative overproduction of immature white cells, and great enlargement of the 

 spleen. The disease is variable, at times running a more chronic course in adults than 

 in children. It is almost always fatal, although its progress can sometimes be delayed 

 by radiation or by chemical agents. It can be produced in some animals by long- 

 continued exposure to low intensities of ionizing radiation. 



lifetime: A synonym for (a) mean life, (b) half-life. 



Lindemann electrometer: A type of electrometer employing a metalized quartz 

 fiber mounted on and perpendicular to a quartz torsion fiber in such a way that the 

 former fiber is positioned in a system of electrodes. 



linear absorption coefficient : A factor expressing the fraction of a beam of radiation 

 absorbed in unit thickness of material. 



linear accelerator : A device for accelerating particles employing alternate electrodes 

 and gaps arranged in a straight line, so proportioned that, when their potentials are 

 varied in the proper amplitude and frequency, particles passing through them receive 

 successive increments of energy. 



lymph : An almost colorless fluid circulating in the lymphatic vessels of vertebrates. 

 It closely resembles blood plasma in composition and contains lymphocytes. 



lymph node (lymph gland, obs. ) : An aggregation of connective tissue crowded with 

 lymphocytes and surrounded with a fibrous capsule. It is provided with incoming 

 and outgoing lymph vessels and a plexus of internal lymph spaces. 



lymphocyte : A type of leukocyte characterized by a single sharply defined nucleus 

 and scanty cytoplasm. Small lymphocytes constitute about 25 per cent of the white 

 corpuscles of the circulating blood in adult men. 



lymphopenia : Decrease in the proportion of lymphocytes in the blood. 



mass absorption coefficient : The linear absorption coefficient per centimeter divided 

 by the density of the absorber in grams per cubic centimeter. 



mass spectrograph : A device for analyzing a substance in terms of the mass /charge 

 ratios of its components. The term is usually restricted to devices that produce a 

 focused mass spectrum of lines on a photographic plate. 



mechanical register (counting) : An electromechanical device for recording or reg- 

 istering counts. 



median lethal dose (MLD) : Dose of radiation required to kill, within a specified 

 period, 50 per cent of the individuals in a large group of animals or organisms. 



median lethal time (MLT) : Time required, following administration of a specified 

 dose of radiation, for the death of 50 per cent of the individuals in a large group of 

 animals or organisms. 



