Inelastic QENS Fitting Testing

Prerequisites

  • Download the ISIS Sample Data

  • Make sure that the data set is on your list of search directories

MSD tab

Preparation

Time required 3 - 5 minutes

  1. Go to Interfaces > Inelastic > QENS fitting

  2. Go to the MSD tab

  3. Click Add Workspace

  4. With the combo box set to File click browse and select the file that you saved in the previous test

  5. Check All Spectra

  6. Click Add and close the dialogue.

  7. Set Fit type to Gaussian

  8. Click Run

  9. This should produce a plot of the fitted function in the interface

  10. Change End X to 1.0

  11. Click Run

  12. Repeat the previous steps with Peters and Yi functions

  13. Try run fits using the different Minimizer options (except FABADA), each time change the End X value either + or - 0.1

I(Q, T) tab

Preparation

Time required 3 - 5 minutes

  1. Go to Interfaces > Inelastic > QENS fitting

  2. Go to the I(Q, T) tab

  3. Click Add Workspace

  4. With the combo box set to Workspace select the _iqt workspace from the previous test

  5. Check All Spectra

  6. Click Add and close the dialogue.

  7. Set Exponential to 1

  8. In the data table set EndX for WS Index 0 to 0.14

  9. Using shift select the EndX for all spectra and click unify range, this should set the EndX for all spectra to 0.14

  10. Click Run

  11. This should produce a fit and a difference plot in the window

  12. Click Plot current preview this should open a plot with three datasets plotted

  13. Select the runs 6 - 50 and click Remove

  14. Click Run

  15. Select Lifetime from the Output drop-down

  16. Click Plot this should open a new plot with the lifetimes plotted

Convolution tab

Preparation

Time required 3 - 5 minutes

  1. Go to Interfaces > Inelastic > QENS fitting

  2. Go to the Convolution tab

  3. Click Add Workspace

  4. With the combo box’s set to File

  5. Click browse and load the irs26176_graphite002_red.nxs file from the sample data

  6. Click browse and load the resolution file irs26173_graphite002_res.nxs from the sample data

  7. In Workspace Indices enter 0-5

  8. Click Add and close the dialogue.

  9. Set Lorentzians to 2

  10. Set Max iterations to 400

  11. Click Run

  12. Three new workspaces should be created in the main GUI - Parameters, Result and Workspaces

  13. In the Mini plots widget, change Plot Spectrum to 3

  14. Click Fit Single Spectrum the plot should update and new workspaces are created in the main Mantid GUI

  15. Remove spectra 0-2, then remove spectra 5. do these as separate removals.

  16. Click Run; the plot should update and new workspaces are created in the main Mantid GUI

  17. Try the various Plot options in the interface

    1. Output drop-down set to All and click Plot - should give 5 separate plots per input spectra

    2. Plot Current Preview - should result in a plot with three datasets

    3. Enable the Plot Guess checkbox - should not change anything, but should not break anything either!

  18. Change the Fit type to different functions and run fits

Function (Q) tab

Preparation

Time required 3 - 5 minutes

  1. Go to Interfaces > Inelastic > QENS fitting

  2. Go to the Function (Q) tab

  3. Click Add Workspace

  4. With the combo box set to Workspace select the 0-5__Result workspace from the previous test

  5. In Parameter Name select f1.f0.FWHM

  6. Click Add and close the dialogue.

  7. Under Fit Type select TeixeiraWater

  8. Click Run

  9. Three new workspaces should be created in the main GUI - Parameters, Result and Workspaces

  10. Change the Fit type to different functions and run fits