Search results
Results from the WOW.Com Content Network
Caesium-137 (137 55 Cs), cesium-137 (US), [7] or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from spontaneous fission of uranium-238. It is ...
The official definition of the second was first given by the BIPM at the 13th General Conference on Weights and Measures in 1967 as: "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.
Since 1967, the official definition of a second is: The second, symbol s, is defined by taking the fixed numerical value of the caesium frequency, Δν Cs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, [9] to be 9 192 631 770 Hz, which is equal to s −1.
The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom 13th CGPM Resolution 1 CIPM 1967 This definition implies that the caesium atom is at rest and unperturbed.
Caesium (IUPAC spelling; [9] also spelled cesium in American English) is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C (83.3 °F; 301.6 K), which makes it one of only five elemental metals that are liquid at or near room temperature.
A new sealed cesium-137 radiation source as it appears in its final state. A radioactive source is a known quantity of a radionuclide which emits ionizing radiation, typically one or more of the radiation types gamma rays, alpha particles, beta particles, and neutron radiation.
In 1997, the International Committee for Weights and Measures (CIPM) added that the preceding definition refers to a caesium atom at rest at a temperature of absolute zero. [21]: 113 Following the 2019 revision of the SI, the definition of every base unit except the mole and almost every derived unit relies on the definition of the second.
Subsequently, caesium-137 radiation contamination was found at a furnace in Singapore which had accepted scrap metal from the Kambalda operation. After years of negotiation, 119 drums of slightly contaminated waste, holding bricks and sludge from the Singapore furnace, were eventually transported to Western Australia in December 1981 and stored ...