X unit

Physical unit
Unit name	X unit
Unit symbol	${\displaystyle \mathrm {XE} }$ or ${\displaystyle \mathrm {xu} }$
Physical quantity (s)	length
Formula symbol	${\displaystyle l}$
dimension	${\displaystyle {\mathsf {L}}}$
In SI units	${\displaystyle \mathrm {1\,XE\approx 1{,}002\,1\cdot 10^{-13}\;m} }$

The X unit (XE) or Siegbahn unit is a unit of length outside of the SI system .

history

The X moiety in 1925 by the Swedish physicist Karl Manne Siegbahn defined as 1 / 3029.04 of the spacing of (200) - lattice planes of calcite at 18 ° C. Siegbahn wanted a unit that corresponds to about 10 ⁻¹³  m (0.1  picometer ). In fact, it is (1.00206 ± 0.00005) · 10 ⁻¹³  m.

It was used in X-ray spectroscopy until 1965, when it was replaced by the Ångström .

swell

• JA Bearden: X-Ray Wavelength Conversion Factor Λ (λ _g / λ _s ) . In: Physical Review . tape 137 , 1B, 1965, pp. B181 , doi : 10.1103 / PhysRev.137.B181 (length of the X unit in metric units).