actinium(A radioactive element of the actinide series, occurring as a decay product of uranium. It is used as an alpha particle source and in neutron production)
activated carbon(A powdered, granular or pelleted form of amorphous carbon characterized by a very large surface area per unit volume because of an enormous number of fine pores)
activated sludge(Sludge that has been aerated and subjected to bacterial action; used to speed breakdown of organism matter in raw sewage during secondary waste treatment)
active participation(The involvement, either by an individual or a group of individuals, in their own governance or other activities, with the purpose of exerting influence)
