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# QE Coverage¶

## Overview¶

QECoverage is a small planning tool to allow inelastic neutron scattering users to determine graphically the momentum / energy transfer limits for a given spectrometer and fixed energy.

## Options¶

To use, select the geometry (direct or indirect) and instrument from the tabs and drop-down menu. For direct geometry spectrometers, an incident energy (Ei) in meV must be given; for indirect geometry machines, the final energies are fixed at a few values which must be selected from the drop-down menu. (Negative values of Ei are treated as positive - the program only uses the magnitude of Ei).

To overplot the calculated Q-E trajectories, set the “Plot Over” check box.

The plot range is from Emin to Ei for direct, and from -Ef to Emax for indirect geometry spectrometers, and Emin and Emax may be inputted in the appropriate text box. If this box is left empty, Emin=-Ei (Emax=Ef) is set automatically for direct (indirect) geometry.

You can choose to create a 1D Mantid workspace for latter plotting using the “Create Workspace” check box.

In addition, for HYSPEC, where the detector bank can be rotated, an additional
parameter **S2** denoting the scattering angle of the center of the detector
bank is required. The detectors extend over 60 degrees, so the two theta limits
will be taken from max([0, abs(s2)-30]) to abs(s2)+30.

The Q(E) trajectory is calculated from the kinematic conditions:

\(\Delta E = E_i - E_f\)

and

\(\frac{\hbar^2 \mathbf{Q}^2}{ 2 m_n } = E_f + E_i - 2 \sqrt{E_i E_f} \cos{2\theta}\)

which is then solved for known \(E_i\) (\(E_f\)) for direct (indirect) geometry.

**Category**: Interfaces