| actinium |
a radioactive chemical element of the rare-earth group that has eighty-nine protons in each nucleus. (symbol: Ac) |
| aluminum |
a chemical element that has thirteen protons in each nucleus, occurs commonly in ores such as bauxite, and in pure form is a strong lightweight corrosion-resistant silvery metal with many industrial uses. (symbol: Al) |
| americium |
a synthetic radioactive chemical element that has ninety-five protons in each nucleus. (symbol: Am) |
| amitosis |
direct cell division in which the nucleus divides without the formation of chromosomes. (Cf. mitosis.) |
| antimony |
a chemical element that has fifty-one protons in each nucleus and forms a brittle bluish white metal crystal, used in hard alloys, electrical components, and medicines. (symbol: Sb) |
| argon |
a chemical element of the inert gas group that has eighteen protons in each nucleus. (symbol: Ar) |
| arsenic |
a poisonous chemical element that has thirty-three protons in each nucleus and occurs in brittle, grayish white crystalline masses or in yellow or black allotropes. (symbol: As) [1/2 definitions] |
| astatine |
a highly radioactive chemical element of the halogen group that has eighty-five protons in each nucleus. (symbol: At) |
| atomic number |
the number of protons or positive electrical charges in the nucleus of one atom of a given element. [1/2 definitions] |
| autogamy |
in biology, self-fertilization by the reuniting of two nuclei that originated in the splitting of a single nucleus, as in certain protozoa, algae, and fungi. [1/2 definitions] |
| barium |
a chemical element of the alkaline-earth group that has fifty-seven protons in each nucleus and that is usu. found in compounds such as salts. (symbol: Ba) [1/2 definitions] |
| berkelium |
a radioactive synthetic metal element of the actinide series that has ninety-seven protons in each nucleus. (symbol: Bk) |
| beryllium |
a chemical element of the alkaline-earth group that has four protons in each nucleus and occurs in pure form as a hard, light, gray solid, chiefly used in alloys with copper and in aerospace material. (symbol: Be) |
| beta particle |
a high-speed positron or electron ejected from a nucleus in radioactive decay or fission. |
| bismuth |
a chemical element that has eighty-three protons in each nucleus and is a white brittle crystalline metal with very low thermal and electrical conductivity, used chiefly in alloys and medicines. (symbol: Bi) |
| boron |
a chemical element that has five protons in each nucleus and that occurs naturally only in compounds such as boric acid and borax. (symbol: B) |
| bremsstrahlung |
electromagnetic radiation, such as x-rays, produced by the sudden deceleration or acceleration of an electron caused by its approach to an atomic nucleus. |
| bromine |
a chemical element of the halogen group that has thirty-five protons in each nucleus, occurring as a toxic, volatile, dark reddish brown liquid or in various compounds such as acids and salts. (symbol: Br) |
| cadmium |
a chemical element that has forty-eight protons in each nucleus and occurs in various compounds or in pure form as a soft bluish white metal. (symbol: Cd) |
| calcium |
a chemical element of the alkaline-earth group that has twenty protons in each nucleus and occurs widely in nature, but only in compounds such as calcite or limestone. (symbol: Ca) [1/2 definitions] |
| californium |
a synthetic radioactive chemical element having ninety-eight protons in each nucleus. (symbol: Cf) |