GLOSSARY OF SELECTED TERMS IN NUCLEAR SCIENCE 437 



microcurie: One-millionth of a curie; symbol mc 



millicurie: One-thousandth of a curie; symbol me. _ . , ,, 



million electron volts: A common unit of energy in nuclear science, equivalent to 

 10« ev; symbol Mev. See electron volt. 



milliroentgen : One-thousandth of a roentgen. , • :„„ 



mole fraction: As used in isotope separation, the number of atoms of a certain iso- 

 tope of an element expressed as a fraction of the total number of atoms of thnt <>l<Mnent 



nresent in the isotopic mixture. 



r^onitoring : Periodic or continuous determination of the an.ount c>t lonizmg radia- 

 tion or radioactive contamination present in an oc.-upied region, or m a person, as a 

 safety measure for purposes of health protection. . ^. . , . „, ,. ^,. 



monochromatic radiation: Electromagnetic radiation ot a single wavelength, oi 

 r'ldi-itiou ill wluch all the photons have the same energy. 



morloenergetic radiation: Particulate radiation of a given type (alpha, beta, neu- 

 tron etc ) in which all the particles have the same energy. 



mucosa- AIu,.ous membrane lining the gastrointestinal tract and air passages. 

 Ttural radioactivity: Radioactivity exhibited by naturally occurring -^>- --- 

 Natural radionuclides may be classified as follows: (a) Primary, which have hfet mes 

 excredtglveral hundred' million years and which presumably have persisted rom 

 the tie of nucleogenesis to the present. They include the alpha emitters U-«, U 

 Th^'rild Sm- and the beta-active nuclides K« Rb", La-, In-, Lu- and Re-. 

 rM ^eeondarv which have geologically short lifetimes and are decay products oi pri- 

 mly na:itT;adt:L4ides.^ Alf presently known members of this class bdong to the 

 Sements from thallium to uranium. Those derived from U-« are members of the 

 uranium or radium, series; those from U^S of the actinium series; and those from 

 Th- ot'the thorium series, (c) Induced, which have geologically short lifetimes and 

 are p;oducts of nuclear reactions occurring currently or recently in --^^ ^xan.^^^^^^^ 

 are C- (natural radiocarbon), produced by cosmic-ray neutrons m the ^tmosphere 

 Tnd Pu'^- produced in uranium minerals by neutron capture, (d) Extinct, wh h 

 have lifetimes that are too short for survival from the time of nucleogenesis to the 

 present, but long enough for persistence into early geologic times with measurable 

 effects. At present, I'-'" is the only suspected member of this class. 



necrosis : Death of a circumscribed portion of tissue. , „^,,,,npd 



neoplasm : A new growth of cells which is more or less unrestrained and not governed 

 by the'usual limitations of normal growth. Benign : If thei-e is some degree of grow^a 

 restraint and no spread to distant parts. Malignant: It the growth invades the tis- 

 sues of the host, spreads to distant parts, or both. t. ■ i r ^ +.. hp n 

 neutron: A neutral elementary particle of mass number 1. It - believed to b a 

 constituent particle of all nuclei of mass number greater thanl. It ^^ instable wi h 

 respect to be'ta decay, with a half-life of about 12 mm. It P-f^^ ^ ^e^^^^^^^^^^ 

 mary ionization in its passage through matter but mteracts with matter predominantly 

 by collisions and, to a lesser extent, magnetically. 



neutron flux : A term used to express the intensity of neutron radiation. The num 



";:lt;r = :T^ t::^::^^^ ;^ "Z... . nudear reaction for the 



^3^:.:^: " T^X atom characterized by the charge, mass nun... .nd 

 quantum state of its nucleus. A nuclide, (b) A nucleus of given charge, mass num- 

 ber, and quantum .state. Also a collection of such nuclei. 



nucleic acid: A constituent of the cell nucleus, composed of a unu.n ^^^^^f^d 

 phone acid, nbose or desoxyribose, and the four bases adenine, guanine, cystosint, and 

 uracil (or thymine). 



