Chemical, usually acetic acid in the fixer and sodium carbonate in the developer, to neutralize the developer and to swell the gelatin, respectively.

See also Film Processor and X-Ray Film.

The active zone on an image is the zone available for processing. When a zone is activated, its border has sizing handles.

Activity is the rate of radioactive decay or the emission rate of a radiation from radioactive material. The cumulated activity is useful for nuclides that emit multiple radiations per disintegration.
The units for activity are the curie (Ci) and the becquerel (Bq).

The acute dose is the amount of energy accommodated in human tissue or in biological systems.

See also Acute Exposure, Acute Radiation Syndrome, Biodosimetry and Annual Limit On Intake.

An acute exposure is a short, powerful exposure to radiation, toxic materials or microorganism, generally lasting less than one day.