WAY TO KNOWLEDGE...

                               ATOMIC CLOCK

FOCS 1, a continuous cold caesium fountain atomic clock in Switzerland, started operating in 2004 at an uncertainty of one second in 30 million years

     Since long, man has used clocks and watches to measure time. But those were crude watches and didn't measure time accurately. A few years ago, scientists were able to develop a very sophisticated clock known as ATOMIC CLOCK. With its development a new era has been ushered in the field of time measurement. It is a wonder clock, that remains accurate to one second in 1,700,000 years.

     Today we have mainly three types of clocks and watches : mechanical, electrical and electronics.
MECHANICAL CLOCKS and WATCHES are spring driven; ELECTRIC CLOCKS are battery powered and the ELECTRONIC ones are quartz based. All these clocks and watches show time quite accurately. But if they run continuously for long period, they can get slow or fast.

     Now the smallest internationally accepted unit of time is the ATOMIC SECOND. It is based on atomic clock, and defined as the time interval during which exactly 9192631770 cycles of the hyperfine resonance frequency of the ground state of the caesium atom occur. Prior to this the second was the standard of time which was measured as a portion of earth's rotation as 1/86400th of a day. An atomic clock uses the frequencies produced by atoms or molecules. The time is measured by counting the number of vibrations. Most of the atomic clock make use of frequencies in the microwave range from about 1400 to 40,000 MHz.

    In 1947, an oscillator controlled by frequencies of AMMONIA MOLECULE was constructed. An ammonia controlled clock was built in 1949 at the National Bureau of Standards, Washington D.C.

     In 1955, a CAESIUM-BEAM atomic clock of high precision was first put in operation at the National Physics Laboratory, Teddington, England. After that a number of laboratories started producing commercial models of caesium-beam atomic clocks.

Caesium Beam Tube

                                         
     In the Caesium clock, the Caesium is heated in a small oven. The Caesium produces a beam which is directed through an electromagnetic field. The 5 MHz output from a quartz clock is multiplied to give 9192631770 Hz that controls the electromagnetic field. Part of the 5 MHz output is used to derive a clock display unit which indicates time.