Unit Factory¶

What is it?¶

The Unit Factory is a Dynamic Factory that creates and hands out instances of Mantid Unit objects.

Available units¶

The following units are available in the default Mantid distribution.

Name	ID (as known by Unit Factory)	Unit	Relevant equation
Time of flight	TOF	$\mu s$	TOF
Wavelength	Wavelength	$\mathrm{\AA}$	$\lambda = \frac{h}{p} = \frac{h \times \mathrm{tof}}{m_N \times L_{tot}}$ (see below)
Energy	Energy	$meV$	$E = \frac{1}{2} mv^2 = \frac{m_N}{2} \left ( \frac{L_{tot}}{\mathrm{tof}} \right )^2$
Energy in wavenumber	Energy_inWavenumber	$cm^{-1}$	$8.06554465 \times E$
Momentum (k)	Momentum	$\mathrm{\AA}^{-1}$	$k = \frac{2 \pi }{\lambda}=\frac{2 \pi \times m_N \times L_{tot}}{h \times \mathrm{tof}}$
d-spacing	dSpacing	$\mathrm{\AA}$	$d = \frac{n \, \lambda}{2 \, sin \, \theta}$
Momentum transfer (Q)	MomentumTransfer	$\mathrm{\AA}^{-1}$	$Q = 2 \, k \, sin \, \theta = \frac{4 \pi sin \theta}{\lambda}$
Momentum transfer squared ( $Q^2$ )	QSquared	$\mathrm{\AA}^{-2}$	$Q^2 \frac{}{}$
Energy transfer	DeltaE	$meV$	$\Delta E = E_{i}-\frac{1}{2}m_N \left ( \frac{L_2}{\mathrm{tof}-L_1\sqrt{\frac{m_N}{2E_i}}} \right )^2$
Energy transfer in wavenumber	DeltaE_inWavenumber	$cm^{-1}$	$8.06554465 \times \Delta E$
Spin Echo Length	SpinEchoLength	$nm$	$constant \times \lambda^2$ The constant is supplied in eFixed
Spin Echo Time	SpinEchoTime	$ns$	$constant \times \lambda^3$ The constant is supplied in eFixed

Where $L_1$ and $L_2$ are sample to the source and sample to detector distances respectively, $L_{tot} = L_1+L_2$ and $E_i$ is the energy of neutrons leaving the source. $\theta$ here is the Bragg scattering angle (e.g. half of the $\theta$ -angle used in spherical coordinate system directed along Mantid z-axis)

Note on Wavelength: If the emode property in ConvertUnits is specified as inelastic Direct/Indirect (inelastic) then the conversion to wavelength will take into account the fixed initial/final energy respectively. Units conversion into elastic momentum transfer (MomentumTransfer) will throw in elastic mode (emode=0) on inelastic workspace (when energy transfer is specified along x-axis)

Adding new units¶

Writing and adding a new unit is relatively straightforward. Instructions will appear here in due course. In the meantime if a unit that you require is missing, then please contact the development team and we will add it to the default Mantid library.

Category: Concepts