ETYM Cf. French atomique.
1. Immeasurably small; SYN. atomlike, minute.
2. Of or relating to of comprising atoms.
Of atoms.

1. Constituting or like a nucleus
2. (Of power and warfare and weaponry) Using atomic energy; SYN. atomic.
3. (Physics) Pertaining to nuclear fission or fusion.
4. (Biology) Pertaining to a cell's nucleus

An apparatus for imparting high velocities to charged particles (as electrons). atom-smasher

1. A pedal that controls the throttle valve; SYN. accelerator pedal, gas pedal, gas, throttle, gun.
2. A valve that regulates the supply of fuel to the engine; SYN. throttle, throttle valve.
3. Increases the kinetic energy of charged particles; SYN. particle accelerator, atom smasher.

Or proton number; The number (symbol Z) of protons in the nucleus of an atom. It is equal to the positive charge on the nucleus. In a neutral atom, it is also equal to the number of electrons surrounding the nucleus. The 109 elements are arranged in the periodic table of the elements according to their atomic number. See also nuclear notation.
The order of an element in Mendeleyev's table of the elements; equal to the number of protons in the nucleus or electrons in the neutral state of an atom of an element.
The number of protons in a nucleus. It determines the chemical properties of an element.

A device for the controlled release of nuclear energy (as for producing heat).

A timepiece that derives its time scale from the vibration of atoms or molecules.
Timekeeping device regulated by various periodic processes occurring in atoms and molecules, such as atomic vibration or the frequency of absorbed or emitted radiation.
The first atomic clock was the ammonia clock, invented at the US National Bureau of Standards 1948. It was regulated by measuring the speed at which the nitrogen atom in an ammonia molecule vibrated back and forth. The rate of molecular vibration is not affected by temperature, pressure, or other external influences, and can be used to regulate an electronic clock.
A more accurate atomic clock is the cesium clock. Because of its internal structure, a cesium atom produces or absorbs radiation of a very precise frequency (9,192,631,770 Hz) that varies by less than one part in 10 billion. This frequency has been used to define the second, and is the basis of atomic clocks used in international timekeeping.
Hydrogen maser clocks, based on the radiation from hydrogen atoms, are the most accurate. The hydrogen maser clock at the US Naval Research Laboratory, Washington, DC, is estimated to lose one second in 1,700,000 years. Cooled hydrogen maser clocks could theoretically be accurate to within one second in 300 million years.
Atomic clocks are so accurate that minute adjustments must be made periodically to the length of the year to keep the calendar exactly synchronized with the Earth's rotation, which has a tendency to speed up or slow down. There have been 17 adjustments made since 1972. In 1992 the northern hemisphere's summer was longer than usual—by one second. An extra second was added to the world's time at precisely 23 hours, 59 minutes and 60 seconds on 30 June 1992. The adjustment was called for by the International Earth Rotation Service in Paris, which monitors the difference between Earth time and atomic time.