"The improvements that we report in our paper have reduced significantly the caesium fountain clock's two largest sources of measurement uncertainties-Doppler shifts and the microwave-lensing frequency shift," said NPL Project Leader Krzysztof Szymaniec.
The physicists evaluated the recently upgraded caesium fountain clock with physical measurements at NPL and mathematical models developed at Penn State.
This time has now been considerably reduced with the aid of a new method developed at the Physikalisch-Technische Bundesanstalt (PTB), which makes the output frequency of the caesium fountains more stable.
For excitation of the caesium atoms, the PTB physicists make use of a novel microwave source.
Now, these previous competitors can complement one another, and the technology of the optical clock leads to a considerable improvement of the established caesium clocks.
Caesium fountains are more accurate than "normal" atomic caesium clocks, because in fountains, the caesium atoms are cooled down with the aid of laser beams and come ever slower.
By contrast, edible wild mushrooms (chanterelles, bay boletus, tooth fungus and other known mushrooms) and game (roe deer and stags, for example) and carnivorous freshwater fish (pike and perch for example, in which levels of contamination of 10,000 and 5,000 Bq/kg respectively are on occasion observed) continue to show levels of radioactive caesium above 600 becquerels/kg (Bq).
There is reason for believing that certain Member States and candidate countries which record similar levels of radioactive caesium deposits may have comparable levels of contamination of wild meat.
Regulation 737/90/EEC of March 22, 1990 on conditions for importing agricultural produce from third countries following the accident at the Chernobyl nuclear power station, sets maximum radioactive caesium tolerances for farm produce from third countries destined for human consumption, with compliance subject to controls by the Member States.
(1) A geographic map can be found in: Atlas of caesium deposition on Europe after the Chernobyl accident, Luxembourg, Office for Official Publications of the European Communities, 1998, EUR 16733, ISBN 92-828-3140-X