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A caesium atomic fountain used as part of an atomic clock. The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency.
Many corporations have such standards, which define some terms and symbols specific to them; on the national and international level, ASME standard Y14.38 [1] is one of the standards. Australia utilises the Technical Drawing standards AS1100.101 (General Principals), AS1100-201 (Mechanical Engineering Drawing) and AS1100-301 (Structural ...
The SI second is defined as a certain number of unperturbed ground-state hyperfine transitions of the caesium-133 atom. Caesium standards are therefore regarded as primary time and frequency standards. Caesium clocks include the NIST-F1 clock, developed in 1999, and the NIST-F2 clock, developed in 2013. [67] [68]
Sizes of drawings typically comply with either of two different standards, ISO (World Standard) or ANSI/ASME Y14.1 (American). The metric drawing sizes correspond to international paper sizes . These developed further refinements in the second half of the twentieth century, when photocopying became cheap.
NIST-F1 is a cesium fountain clock, a type of atomic clock, in the National Institute of Standards and Technology (NIST) in Boulder, Colorado, and serves as the United States' primary time and frequency standard. The clock took fewer than four years to test and build, and was developed by Steve Jefferts and Dawn Meekhof of the Time and ...
ISO Standards Handbook – Technical drawings, a broad collection of all basic ISO drawing standards Vol.1 Technical drawings in general, ISBN 92-67-10370-9; Vol.2 Mechanical engineering drawings, construction drawings, drawing equipment, ISBN 92-67-10371-7; ISO 128 Technical drawings—General principles of presentation
The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by the English physicist Louis Essen in 1955 at the National Physical Laboratory in London. [207] It was calibrated by the use of the astronomical time scale ephemeris time (ET). [208]
Caesium-135 is a mildly radioactive isotope of caesium with a half-life of 1.33 million years. It decays via emission of a low-energy beta particle into the stable isotope barium-135. Caesium-135 is one of the seven long-lived fission products and the only alkaline one.