ConstantID

Copper x unit

UnitsMeasured

xu(Cu Kα1) = 1.002 076 97(28) × 10−13 m

Value
1.002 076 97 × 10−13 m
Standard uncertainty
2.8 × 10−20 m
Relative uncertainty
2.8 × 10−7 (279 parts per billion)
Status
Measured
Symbol
xu(Cu Kα1)
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# Copper x unit, CODATA 2022 (NIST)
copper_x_unit = 1.00207697e-13  # m, standard uncertainty 2.8e-20

# SciPy: scipy.constants.physical_constants['Copper x unit']

What it is

An X-ray unit of length, about 10⁻¹³ m, defined so that the wavelength of the copper Kα₁ line is exactly 1537.400 xu(Cu Kα₁). Older crystallography papers use it.

In other units

UnitValue
CGS (cm)1.002 076 97 × 10−11
pm picometre0.100 207 697
fm femtometre100.207 697
Å ångström0.001 002 076 97
a₀ bohr (atomic unit)0.001 893 651 03unit is itself measured

Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display. The relative uncertainty is unchanged by conversion to an exactly defined unit.

How the value changed, 1998–2022

Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).

Copper x unit: CODATA values 1998–2022 relative to the 2022 value, in parts per billion, with one-standard-uncertainty bars−750−500−2500+250+500+750parts per billion1998200220062010201420182022

Relative uncertainty

Copper x unit: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻⁸10⁻⁷10⁻⁶1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20221.002 076 97(28) × 10−132.8 × 10−7 +0.0 σ of 2018
20181.002 076 97(28) × 10−132.8 × 10−7 +0.0 σ of 2014
20141.002 076 97(28) × 10−132.8 × 10−7 +0.0 σ of 2010
20101.002 076 97(28) × 10−132.8 × 10−7 −0.1 σ of 2006
20061.002 076 99(28) × 10−132.8 × 10−7 −0.4 σ of 2002
20021.002 077 10(29) × 10−132.9 × 10−7 +0.2 σ of 1998
19981.002 077 03(28) × 10−132.8 × 10−7

“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).