The atom or nucleus in an atomic or nuclear reaction which is initially stationary.

An index card or test document used to assist, reference, or calibrate equipment.

1. In an x-ray tube, the anode or anticathode which emits x-rays when bombarded with electrons.

2. In a television camera tube, the storage surface that is scanned by an electron beam to generate an output signal current corresponding to the charge-density pattern stored there.

3. In a cathode-ray tuning indicator tube, one of the electrodes that is coated with a material that fluoresces under electron bombardment.

1. The sliding weight on a leveling rod used in surveying to enable the staffman to read the line of collimation.

2. The point that a borehole or an exploratory work is intended to reach.

3. In radar and sonar, any object capable of reflecting the transmitted beam.

1. A geographical area, complex, or installation planned for capture or destruction by military forces.

2. A paper or pasteboard item of square or rectangular shape designed to be fired upon from a specified range during practice or while testing an automatic firearm such as an automatic rifle, machine gun, or submachine gun; it is used to establish a degree of accuracy; it usually consists of a series of geometric patterns of various shapes on a common background.

An object or substance subjected to bombardment or irradiation by particles or electromagnetic radiation.