GLOSSARY OF SELECTED TERMS IN NUCLEAR SCIENCE 431 



nuclide, beius foniu-d citlRT directly or as the result of successive transforniiitions in 

 a radioactive series. A decay product may be either radioactive or stable. 



decontamination : (a) The removal of unwanted radioactive substances from a 

 desired material, e.g., removal of fission products from jilutonium or uranium, (b) 

 The removal of undesired dispersed radioactive material from personnel, instruments, 

 rooms, equipment, etc. 



densitometer: Instrument for measuring photographic density. 



density (photographic): Logarithm of opacity of exposed and processed film. 

 Opacity is tlic reciprocal of transmission; transmission is the ratio of transmitted to 

 incident intensity. Density is used to denote the degree of darkening of photographic 

 film. 



desorption : The reverse process of adsorption whereby adsorbed matter is removed 

 from the adsorbent. The term is also used for the reverse process of absorjjtion. 



detector (radiation) : .\ny device for converting radiant energy to a form more suit- 

 able for obser\ation. 



differential absorption ratio : Ratio of the concentration of an isotope in a given 

 organ or tissue to the concentration that would be obtained if the same administered 

 quantity of this isotope were uniformly distribrted throughout the body. 



discriminator : See pulse-height discriminator. 



disintegration (nuclear) : A spontaneous nuclear transformation (radioactivity) 

 characterized by the emission of energy from the nucleus. When numbers of nuclei 

 are involved, the process is characterized by a definite half-life. 



disintegration constant : The fraction of the number of atoms of a radioactive 

 isotope wliii'li decay in unit time. 



disintegration rate : Rate of decay of radioactive substance. It is usually expressed 

 as disintegrations per unit time. 



dose (dosage) : According to current usage, the radiation delivered to a specified 

 area or volume or to the whole body. Units for dose specification are roentgens for 

 X or gamma rays, reps or equivalent roentgens for beta rays. The subject of dose 

 units for particulate radiation and for very high-energy X rays has not been settled. 

 In radiology the dose may be specified in air, on the skin, or at some depth beneath the 

 surface; no statement of dose is complete without the specification of location. The 

 entire question of radiation dosage units is under consideration by the International 

 Congress of Radiology, and it is expected that new imits based on tlie energy absorbed 

 in tissue will be adopted (see text). 



dose, threshold : See threshold dose. 



dose, tissue : See tissue dose. 



dose, tolerance: See tolerance dose. 



dose-effect curve: A curve relating the dose of radiation to the effect produced. 



dose fractionation : A method of administration of radiation in which relatively 

 small doses are given daily or at longer intervals. 



dose meter ('dosimeter) : Any instrument that measures radiation dose. 



dose rate (dosage rate) : Radiation dose delivered per unit time. 



dose-rate meter : Any instrument that measures radiation dose rate. 



effective half-lif e : Half-life of a radioactive isotope in a biological organism, result- 

 ing from the combination of radioactive decay and biological elimination. 



^_ biological half-life X radioactive half-life 



Effective half-life = ^ . 



biological half-life -|- radioactive half-life 



efficiency (counters) : A measure of the probability that a count will be recorded 



