Varian Associates pre-production rubidium-vapor frequency standard

Varian Associates pre-production rubidium-vapor frequency standard

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Description
Varian, Inc. pre-production rubidium-vapor frequency standard, enclosed in metal frame, with two components in separate small metal cases.
In this accession (no. 1980.0511), the pre-production (.01) and production (.02) model frequency standards show the intermediate and final instruments in the process of developing the rubidium-vapor absorption frequency standard from a laboratory apparatus into a commercially viable, production-line "atomic clock."
History and basic principles
Object ID no. 1980.0511.01 is one of the two pre-production models of an atomic absorption clock that Varian, Associates delivered to NASA’s Jet Propulsion Laboratory in October 1960 for use in tracking space vehicles. It employs many standard commercial components (e.g., power supply, modulation oscillator). Consequently it is far less compact than Object ID no. 1980.0511.02, the V-4700A production model put on the market a year later.
Earlier devices in the development employed sodium in the absorption cell, but it was concluded that the optimum atom for an absorption clock was rubidium, an element similar to sodium and cesium, lying between them in atomic weight. For its commercial models, Varian adopted rubidium.
Brief description of an atomic clock
Electromagnetic waves of very specific and consistent frequencies can induce atoms to fluctuate between two energy states, and by measuring that frequency we can determine the “tick” of an atomic clock. A second in a cesium clock, for example, is defined as 9,192,631,770.0 cycles of the frequency that causes the cesium atom to jump between those states. Different atoms “tick” at different rates – strontium atoms tick about 10,000 times faster than cesium atoms – but all atoms of a given element tick at the same rate, making atomic clocks much more consistent than clocks based on macroscopic objects such as pendulums or quartz crystals.
(Ref: Steven Jefferts, physicist, National Institute of Standards and Technology)
There are different types of atomic clocks, the principle behind all of them remains the same. The major difference is associated with the element used and the means of detecting when the energy level changes. The various types of atomic clocks include:
•Cesium atomic clocks employ a beam of cesium atoms. The clock separates cesium atoms of different energy levels by magnetic field.
•Hydrogen atomic clocks maintain hydrogen atoms at the required energy level in a container with walls of a special material so that the atoms don't lose their higher energy state too quickly.
•Rubidium atomic clocks, the simplest and most compact of all, use a glass cell of rubidium gas that changes its absorption of light at the optical rubidium frequency when the surrounding microwave frequency is just right.
For additional background information go to:
http://www.nist.gov/pml/div688/timekeeping.cfm
http://science.howstuffworks.com/atomic-clock.htm
Object Name
Frequency Standard, Rubidium Vapor
date made
1960
maker
Varian Associates
Physical Description
metal; plastic (overall material)
Measurements
overall: 29 1/2 in x 23 in x 21 1/8 in; 74.93 cm x 58.42 cm x 53.6575 cm
ID Number
1980.0511.01
accession number
1980.0511
catalog number
1980.0511.01
Credit Line
Transfer from National Aeronautics and Space Administration, Jet Propulsion Laboratory
See more items in
Medicine and Science: Modern Physics
Data Source
National Museum of American History
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