Samiksha Jaiswal (Editor)

X unit

Updated on
Edit
Like
Comment
Share on FacebookTweet on TwitterShare on LinkedInShare on Reddit
Unit of
  
length

1 xu in ...
  
... is equal to ...

Symbol
  
xu

SI units
  
6987100210000000000♠1.0021×10 m

Natural units
  
7021620070000000000♠6.2007×10 ℓP 6997189370000000000♠1.8937×10 a0

imperial/US units
  
6987100210620000000♠3.9453×10 in

The x unit (symbol xu) is a unit of length approximately equal to 0.1 pm (10−13 m). It is used to quote the wavelength of X-rays and gamma rays.

Originally defined by the Swedish physicist Manne Siegbahn (1886–1978) in 1925, the x unit could not at that time be measured directly; the definition was instead made in terms of the spacing between planes of the calcite crystals used in the measuring apparatus. One x unit was set at  1⁄3029.04 of the spacing of the (200) planes of calcite at 18 °C.

In modern usage, there are two separate x units, which are defined in terms of the wavelengths of the two most commonly used X-ray lines in X-ray crystallography:

  • the copper x unit (symbol xu(Cu Kα1)) is defined so that the wavelength of the Kα1 line of copper is exactly 1537.400 xu(Cu Kα1);
  • the molybdenum x unit (symbol xu(Mo Kα1)) is defined so that the wavelength of the Kα1 line of molybdenum is exactly 707.831 xu(Mo Kα1).

    • The 2006 CODATA recommended values for these units are:

    1 xu(Cu Kα1) = 1.00207699(28)×10−13 m,1 xu(Mo Kα1) = 1.00209955(53)×10−13 m.

    References

    X unit Wikipedia
    (Text) CC BY-SA


    Similar Topics